MAX20446BATGA [MAXIM]
Automotive 6-Channel Backlight Driver with Boost/SEPIC Controller, Hybrid Dimming and I2C Interface;
| 型号： | MAX20446BATGA |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Automotive 6-Channel Backlight Driver with Boost/SEPIC Controller, Hybrid Dimming and I2C Interface |
| 文件： | 总47页 (文件大小：1244K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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MAX20446B
Automotive 6-Channel Backlight Driver with
Boost/SEPIC Controller, Hybrid Dimming and
2
I C Interface
General Description
Benefits and Features
The MAX20446B is a 6-channel backlight driver with boost
controller for automotive displays. The integrated current
outputs can sink up to 130mA LED current each. The de-
vice accepts a wide 4.5V to 36V input voltage range and
withstands automotive load-dump events.
● Wide-Voltage-Range Operation
• Operates Down to 4V Supply After Startup
• Survives Load Dump Up to 52V
● High Integration
• Complete 6-Channel Solution Including Boost
Controller
The internal current-mode-switching DC-DC controller
supports boost or SEPIC topologies, and operates in the
400kHz to 2.2MHz frequency range. Integrated spread
spectrum helps reduce EMI. An adaptive output-voltage-
control scheme minimizes power dissipation in the LED
current-sink paths.
2
• I C Control for Minimum Parts Count
● Robust and Low EMI
• Spread-Spectrum Oscillator
• Phase Shifting
• 400kHz to 2.2MHz Switching-Frequency Range
• Fail-Safe Operation Mode Using the FSEN Pin
2
The device features I C-controlled pulse-width-modula-
tion (PWM) dimming and hybrid dimming. In either case,
the minimum pulse width is 500ns. Optional phase-shifted
dimming of the strings is incorporated for lower EMI.
● Versatile Dimming Scheme Allows Hybrid or PWM-
2
Only Dimming Using DIM Input or I C
• Dimming Ratio > 10000:1 Using Hybrid Dimming
• Dimming Ratio of 10000:1 at 200Hz Using PWM
Dimming
Comprehensive diagnostic information is also available
2
through the I C interface.
The device is available in a 24-pin TQFN package and op-
erates over the -40 to +125°C temperature range.
● Complete Diagnostics
• LED Open/Short Detection and Protection
• Boost Output Undervoltage and Overvoltage
• Boost Voltage
Applications
● Infotainment Displays
● Central Information Displays
● Instrument Clusters
• Individual String LED Current
• Thermal Shutdown
● Compact (4mm x 4mm) 24-Pin TQFN Package
Ordering Information appears at end of datasheet.
19-100905; Rev 1; 1/21
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Simplified Block Diagram
FLTB
BSTMON
OV
COMP
UV
SHORTGND
VBG
LEDUNUSED
LEDSHORT
LEDOPEN
SHORTGND
UV
FAULT
DETECTOR
FAULT FLAG LOGIC
LEDSHORT
LEDOPEN
TSHDN
LEDUNUSED
UV
COMP
COMP
0.4V
VCC
SSDONE
6
g
M
SSDONE
RANGE
PWM
COMP
NDRV
NDRV
EAREF
$ ARRAY=6
LOGIC
V
THH
6
ORPHASE
RTDET
COMPH
8
CONTROL
LOGIC
6
UP/DOWN
COUNTER
DAC
OUT_
BOOSTON
LODIM
6
V
THL
COMPL
RT
OSCILLATOR
6
IREF_
MAX20446B
POK
CS
COMP
SLOPE
COMPENSATION
CURRENT
IMON_
0.425V
DIMPHASE
6
CS
CS BLANKING
20 MHz
CLOCK
FSEN
RTDET
SHORTGND
LEDSHORT
LEDOPEN
LEDUNUSED
OVPUV
TSHDN
ORPHASE
LODIM
THERMAL
SHUTDOWN
DIM LOGIC &
PHASE SHIFTING
LEDGND
PGATE
PRE-
REGULATOR
BOOSTON
PGATE
CONTROL
BANDGAP
VBG
IN
200 mA
UVLO VIN
8
VINUVLO
ADC
REGISTER
MAP &
SCL
SDA
INTERFACE
IMON
MUX
7:1
5V
VCC
STMON
REGULATOR
ISET[3:0]
TONH[17:0]
UVLO
VVCC
VINUVLO
IN
POK
REFERENCE
CURRENT
GENERATION
IREF_
0
EN
COMP
DUTY-CYCLE
MEASUREMENT
1
DIM
TSHDN
EN
20MHz
DIM_EXT
SHDN
POK
GND
PGND
IREF
www.maximintegrated.com
Maxim Integrated | 2
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
TABLE OF CONTENTS
General Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Benefits and Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Simplified Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Absolute Maximum Ratings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Package Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
TQFN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
TQFN-SW. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Typical Operating Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Pin Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
MAX20446B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Pin Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Functional Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
MAX20446B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Detailed Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Undervoltage Lockout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Current-Mode DC-DC Controller. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8-Bit Digital-to-Analog Converter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
FSEN Pin Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Dimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Hybrid Dimming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Hybrid Dimming Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Hybrid Dimming Operation Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Low-Dimming Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Phase-Shift Dimming. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Disabling Individual Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Startup Sequence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Stage 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 3: Boost Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Oscillator Frequency/External Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Spread-Spectrum Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5V LDO Regulator (V ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
CC
LED Current Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Fault Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
www.maximintegrated.com
Maxim Integrated | 3
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
TABLE OF CONTENTS (CONTINUED)
Open-LED Management and Overvoltage Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Short-LED Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Thermal Warning/Shutdown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Analog-to-Digital Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2
I C Interface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Register Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
MAX20446B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Register Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Applications Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
DC-DC Converter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Power-Circuit Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Boost and Coupled-Inductor Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
SEPIC Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Slope Compensation and Current-Sense Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Output Capacitor Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Rectifier Diode Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Feedback Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
External Disconnect-MOSFET Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
V
OUT
to OUT_ Bleed Resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Thermal Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
PCB Layout Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Typical Application Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
MAX20446B Applications Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
www.maximintegrated.com
Maxim Integrated | 4
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
LIST OF FIGURES
Figure 1. Hybrid Dimming Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 2. Hybrid Dimming Operation Modes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Figure 3. Boost Startup with DIS_FASTSS = 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
www.maximintegrated.com
Maxim Integrated | 5
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
LIST OF TABLES
Table 1. FSEN Pin Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2
Table 2. I C Address Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Table 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Table 4. LED Current Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Table 5. Output Current Measurement (IOUT1):. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Table 6. Output Current Measurement (IOUT4):. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Table 7. Output Current Measurement (IOUT5):. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Table 8. Output Current Measurement (IOUT6):. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
www.maximintegrated.com
Maxim Integrated | 6
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Absolute Maximum Ratings
IN, EN, OUT_, BSTMON, PGATE to GND............. -0.3V to +52V
PGND, LEDGND to GND ...................................... -0.3V to +0.3V
Continuous Power Dissipation Multilayer Board (derate
27.8mW/°C above +70°C) ................................................2.857W
ESDHB .................................................................... -2kV to +2kV
ESDMM................................................................-200V to +200V
Operating Temperature Range...........................-40°C to +125°C
Junction Temperature Range .............................-40°C to +150°C
Storage Temperature Range ..............................-65°C to +150°C
Lead Temperature (soldering, 10s)...................................+300°C
V
CC
to GND.......................-0.3V to maximum of (+6, V + 0.3)V
IN
FLTB, SCL, SDA, DIM to GND................................. -0.3V to +6V
CS, RT, COMP, NDRV, IREF, FSEN to GND.......-0.3V to V
+
CC
0.3V
NDRV Peak Current (< 100ns).................................... -5A to +5A
NDRV Continuous Current ............................ -100mA to +100mA
OUT1-6 Continuous Current ......................... -100mA to +150mA
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the
device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for
extended periods may affect device reliability.
Package Information
TQFN
Package Code
T2444+4C
21-0139
90-0022
Outline Number
Land Pattern Number
Thermal Resistance, Single-Layer Board:
Junction to Ambient (θ
)
48°C/W
3°C/W
JA
Junction to Case (θ
)
JC
Thermal Resistance, Four-Layer Board:
Junction to Ambient (θ
)
36°C/W
3°C/W
JA
Junction to Case (θ
)
JC
TQFN-SW
Package Code
Outline Number
T2444Y+4C
21-100290
90-0022
Land Pattern Number
Thermal Resistance, Four-Layer Board:
Junction to Ambient (θ
)
41.3°C/W
3.44°C/W
JA
Junction to Case (θ
)
JC
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates
RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal
considerations, refer to www.maximintegrated.com/thermal-tutorial.
Electrical Characteristics
(V = 12V, R = 76.8kΩ, C
= 1μF, T = T = -40°C to +125°C, unless otherwise noted., (V = 12V, R = 76.8kΩ, C
= 1μF,
VCC
IN
RT
VCC
A
J
IN
RT
T
A
= T = -40ºC to +125ºC, unless otherwise noted. Limits are 100% tested at T = +25ºC. Limits over the operating temperature range
J
A
and relevant supply voltage range are guaranteed by design and characterization.))
PARAMETER SYMBOL CONDITIONS
POWER INPUT
MIN
TYP
MAX
UNITS
Input Operating Range
4.5
36
V
www.maximintegrated.com
Maxim Integrated | 7
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Electrical Characteristics (continued)
(V = 12V, R = 76.8kΩ, C
= 1μF, T = T = -40°C to +125°C, unless otherwise noted., (V = 12V, R = 76.8kΩ, C
= 1μF,
VCC
IN
RT
VCC
A
J
IN
RT
T
A
= T = -40ºC to +125ºC, unless otherwise noted. Limits are 100% tested at T = +25ºC. Limits over the operating temperature range
J
A
and relevant supply voltage range are guaranteed by design and characterization.))
PARAMETER
SYMBOL
CONDITIONS
MIN
4.2
TYP
MAX
36
UNITS
V
Input Voltage Range
After Startup
Input Operating Range
IN pin connected to V
4.5
5.5
15
V
CC
Quiescent Supply
Current
V
DIM
= 5V, V
= 1.3V,
BSTMON
10
0.1
mA
µA
V
OUT1–OUT6 unconnected
Standby Supply Current
V
IN
= 12V, V = 0V
1
EN
Undervoltage Lockout,
Rising
3.8
3.1
4.15
4.45
Undervoltage Lockout,
Falling
3.7
1.2
4
V
2
Startup Delay
From EN high to I C ready
1.8
ms
V
CC
REGULATOR
V
Output Voltage
5.75V < V < 36V; I = 1mA to 10mA
VCC
4.75
5
5.25
0.2
V
V
CC
IN
Dropout Voltage
V
IN
= 4.5V, I
= 5mA
VCC
Short-Circuit Current
Limit
V
CC
shorted to GND
60
mA
V
V
CC
Undervoltage-
Lockout Threshold,
Rising
4.05
3.75
4.2
4.35
4.04
V
CC
Undervoltage-
Lockout Threshold,
Falling
3.9
V
RT OSCILLATOR
Switching-Frequency
Range
f
Frequency dithering disabled
360
2420
kHz
%
SW
f
f
f
= 400kHz
90
86
94.5
90.5
98.5
95
SW
SW
SW
Maximum Duty Cycle
= 2200kHz
Oscillator Frequency
Accuracy
= 400kHz to 2200kHz, frequency
-10
+10
%
dither disabled
Frequency Dither
SS
SSL bit = 1
±3
%
V
RT Output Voltage
Sync Rising Threshold
V
RT
R
RT
= 76.8kΩ or R = 13.3kΩ
1.2
3
1.25
1.3
RT
V
Sync Frequency Duty-
Cycle Range
50
%
1.16 x
1.5 x
Sync Frequency Range
kHz
f
f
SW
SW
MOSFET DRIVER
NDRV On-Resistance,
High Side
NDRV sinking 30mA
NDRV sourcing 30mA
1.5
0.8
3
Ω
Ω
NDRV On-Resistance,
Low Side
1.6
www.maximintegrated.com
Maxim Integrated | 8
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Electrical Characteristics (continued)
(V = 12V, R = 76.8kΩ, C
= 1μF, T = T = -40°C to +125°C, unless otherwise noted., (V = 12V, R = 76.8kΩ, C
= 1μF,
VCC
IN
RT
VCC
A
J
IN
RT
T
A
= T = -40ºC to +125ºC, unless otherwise noted. Limits are 100% tested at T = +25ºC. Limits over the operating temperature range
J
A
and relevant supply voltage range are guaranteed by design and characterization.))
PARAMETER
NDRV Rise Time
SYMBOL
CONDITIONS
MIN
TYP
8
MAX
UNITS
ns
C
C
= 1nF
= 1nF
LOAD
NDRV Fall Time
8
ns
LOAD
SLOPE COMPENSATION
Peak Slope-
Compensation Current-
Ramp Magnitude
Current ramp added to CS
42
50
58
µA
CURRENT-SENSE COMPARATOR
Includes internal slope-ramp magnitude,
Current-Limit Threshold
V
390
420
450
mV
CL_MAX
V
CL
= V
+ slope-compensation voltage
CS
ERROR AMPLIFIER
OUT_ Regulation High
Threshold
V
V
falling
rising
0.95
0.7
1.03
0.78
1.1
V
V
OUT_
OUT_ Regulation Low
Threshold
0.85
OUT_
Transconductance
COMP Sink Current
COMP Source Current
LED CURRENT SINKS
IREF Voltage
500
200
200
700
480
480
880
800
800
µS
µA
µA
V
V
= 2V
= 1V
COMP
COMP
V
R
= 49.9kΩ
1.225
116
96
1.25
120
100
50.6
1.275
124.5
104
V
IREF
IREF
120mA setting
100mA setting
50mA setting
OUT_ Output Current
mA
49
52.2
+2
I
I
= 120mA
= 50mA
= 48V, V
-2
Channel-to-Channel
Matching
OUT_
%
-2.5
+2.5
OUT_
Total OUT_ Leakage
Current to IN
V
OUT_
= 0V, all OUT_ pins
DIM
I
8
12
µA
OUTLEAK
shorted together
OUT_ Current Rise
Time
10% to 90% I
90% to 10% I
150
50
ns
ns
OUT_
OUT_
OUT_ Current Fall Time
DIM Sampling
Frequency
20
MHz
LOGIC INPUT AND OUTPUTS
EN Input Logic-High
EN Input Logic-Low
2.1
2.1
V
V
0.8
5
EN Input Current
V
EN
= 5V
3
µA
DIM, SDA, SCL Input
Logic-High
V
V
DIM, SDA, SCL Input
Logic-Low
0.8
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Maxim Integrated | 9
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Electrical Characteristics (continued)
(V = 12V, R = 76.8kΩ, C
= 1μF, T = T = -40°C to +125°C, unless otherwise noted., (V = 12V, R = 76.8kΩ, C
= 1μF,
VCC
IN
RT
VCC
A
J
IN
RT
T
A
= T = -40ºC to +125ºC, unless otherwise noted. Limits are 100% tested at T = +25ºC. Limits over the operating temperature range
J
A
and relevant supply voltage range are guaranteed by design and characterization.))
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DIM Input Pullup
Current
5
µA
FSEN Input Voltage
Threshold High
FSEN rising
FSEN falling
2.2
V
FSEN Input Voltage
Threshold Logic-Low
V
1.8
V
uA
V
FSENIL
FSEN Input Current
I
V
FSEN
= 1V
15
FSEN
SDA, FLTB Output Low
Voltage
Sinking 3mA
= 5.5V
0.4
+1
FLTB Output Leakage
Current
V
FLTB
-1
µA
OVERVOLTAGE AND UNDERVOLTAGE PROTECTION
BSTMON Overvoltage
Trip Threshold
BSTMON rising
1.18
1.23
70
1.28
V
BSTMON Hysteresis
mV
nA
BSTMON Input Bias
Current
0V < V
< 1.3V
-500
0.4
47.5
4
500
0.46
56.2
18
BSTMON
BSTMON Undervoltage
Detection Threshold
BSTMON falling, PGATE latched off
After ENA is written to '1', FAST_SS = 0
BSTMON falling
0.43
52
V
Boost Undervoltage
Blanking Time
ms
µs
BSTMON Undervoltage
Detection Delay
10
PGATE Pulldown
Current
180
210
2
245
2.2
1
µA
ms
µA
Delay between PGATE going low and
boost converter starting
PGATE Start Delay
PGATE Leakage
Current
V
= 12V, V
= 0V
EN
0.1
PGATE
LED FAULT DETECTION
SLDET[1:0] = 0x01
SLDET[1:0] = 0x10
SLDET[1:0] = 0x11
2.8
5.6
7.5
3
6
8
3.25
6.4
LED Short-Detection
Threshold
V
8.5
Short-Detection
Comparator Delay
9
µs
µA
mV
V
OUT_ Check LED
Source Current
50
60
70
OUT_ Short-to-GND
Detection Threshold
Before boost converter startup
250
1.15
300
1.25
365
1.35
OUT_ Unused Detection
Threshold
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Maxim Integrated | 10
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Electrical Characteristics (continued)
(V = 12V, R = 76.8kΩ, C
= 1μF, T = T = -40°C to +125°C, unless otherwise noted., (V = 12V, R = 76.8kΩ, C
= 1μF,
VCC
IN
RT
VCC
A
J
IN
RT
T
A
= T = -40ºC to +125ºC, unless otherwise noted. Limits are 100% tested at T = +25ºC. Limits over the operating temperature range
J
A
and relevant supply voltage range are guaranteed by design and characterization.))
PARAMETER
SYMBOL
CONDITIONS
During operation
MIN
TYP
MAX
UNITS
OUT_ Open-LED
Detection Threshold
250
300
365
mV
ANALOG-TO-DIGITAL CONVERTER
ADC Measurement
Resolution
8
Bits
mA
mV
Total Measurement
Error, Current
I
= 120mA
-7
+7.5
+70
OUT_
Total Measurement
Error, Voltage
V
= 1V
-50
BSTMON
ADC Gain Error
ADC Offset Error
I
I
= 120mA
= 120mA
-4
-3
+6
+5
%
OUT_
LSB
OUT_
Measurement
Resolution, Current
0.5
5.1
mA
mV
Measurement
Resolution, Voltage
THERMAL SHUTDOWN
Thermal Warning
125
165
°C
°C
Thermal-Shutdown
Threshold
Thermal-Shutdown
Hysteresis
15
°C
2
I C INTERFACE
Serial-Clock Frequency
f
400
kHz
μs
SCL
Bus-Free Time Between
STOP and START
Condition
t
1.3
BUF
START Condition Setup
Time
t
0.6
0.6
0.6
μs
μs
μs
SU:STA
HD:STA
SU:STO
START Condition Hold
Time
t
STOP Condition Setup
Time
t
Clock Low Period
Clock High Period
Data Setup Time
t
1.3
0.6
μs
μs
ns
LOW
t
HIGH
t
100
SU:DAT
HD:DAT
Measured from 50% point on SCL falling
edge to SDA edge
Data Hold Time
t
0
μs
ns
Pulse Width of Spike
Suppressed
t
50
SP
Note 1: Limits are 100% tested at T = +25°C. Limits over the operating temperature range and relevant supply voltage range are
A
guaranteed by design and characterization.
www.maximintegrated.com
Maxim Integrated | 11
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Typical Operating Characteristics
((V = V
= +12V, 6x6 LED load at 100mA, T = +25°C, unless otherwise noted.))
IN
EN
A
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Maxim Integrated | 12
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Typical Operating Characteristics (continued)
((V = V
= +12V, 6x6 LED load at 100mA, T = +25°C, unless otherwise noted.))
IN
EN
A
Pin Configuration
MAX20446B
TOP VIEW
18
17
16
15
14
13
19
20
21
22
23
24
12
11
10
9
CS
IREF
GND
RT
BSTMON
PGND
NDRV
VCC
MAX20446B
LEDGND
SDA
8
+
7
SCL
EN
1
2
3
4
5
6
TQFN
4mm x 4mm
Pin Description
PIN
NAME
FUNCTION
Bias Supply Input. Connect a 4.5V to 36V supply to IN. Bypass IN to GND with a 2.2µF ceramic
capacitor.
1
IN
2
PGATE
OUT1
Gate Connection for External Series pMOSFET
LED String Cathode Connection 1. OUT1 is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT1. OUT1 sinks up to 120mA.
3
LED String Cathode Connection 3. OUT3 is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT3. OUT3 sinks up to 120mA.
4
OUT3
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Maxim Integrated | 13
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Pin Description (continued)
PIN
NAME
FUNCTION
LED String Cathode Connection 5. OUT5 is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT5. OUT5 sinks up to 120mA.
5
OUT5
Open-Drain Fault Output. FLTB asserts low when any diagnostic bit (that is not masked) is
6
FLTB
asserted. See the Fault Protection section for more details. Connect a pullup resistor from FLTB to
V
CC
.
2
7
8
SCL
SDA
I C Clock Input. Connect a pullup resistor from SCL to the logic supply.
2
I C Data I/O Pin. Connect a pullup resistor from SDA to the logic supply.
LED Ground. LEDGND is the return path connection for the linear current sinks. Connect GND,
LEDGND, and PGND at a single point.
9
LEDGND
Oscillator Timing Resistor Connection. Connect a timing resistor (R ) from RT to GND to
RT
program the switching frequency. In addition, connect a 100pF capacitor from RT to GND. To
synchronize the switching frequency with an external clock, apply an AC-coupled external clock at
RT. When the oscillator is synchronized with the external clock, spread spectrum is disabled.
10
RT
Signal Ground. GND is the current return path connection for the low-noise analog signals.
Connect GND, LEDGND, and PGND at a single point.
11
12
GND
IREF
LED Current Reference Input. Connect a resistor (R
= 49.9kΩ) from IREF to GND to set the
IREF
current reference according to the formula IREF = 1.250/R
.
IREF
2
PWM Dimming Input. Apply a PWM signal to DIM for LED dimming control unless I C dimming is
used. Connect DIM to V if dimming control is not used (100% brightness). Connect DIM to GND
if dimming is to be controlled through I C.
13
DIM
CC
2
LED String Cathode Connection 6. OUT6 is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT6. OUT6 sinks up to 120mA.
14
15
16
OUT6
OUT4
OUT2
LED String Cathode Connection 4. OUT4 is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT4. OUT4 sinks up to 120mA.
LED String Cathode Connection 2. OUT2 is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT2. OUT2 sinks up to 120mA.
Fail-Safe Enable Pin. When FSEN is taken high, the boost converter is enabled and the outputs
(OUT1–OUT6) are enabled at 100% duty cycle, independent of all register settings. Connect a
resistor from FSEN to GND to set the LED current; FSEN sets both the LED current (when FSEN
17
FSEN
2
is active) and the I C address (see the MAX20446 FSEN Pin Function section). If the FSEN
function is not needed, connect the pin directly to GND.
Switching-Converter Compensation Input. Connect the compensation network from COMP to GND
for current-mode control (see the Feedback Compensation section for details).
18
19
COMP
CS
Current-Sense Input. CS is the current-sense input for the switching regulator. A sense resistor
connected from the source of the external power MOSFET to PGND sets the switching current
limit. A resistor connected between the source of the power MOSFET and CS sets the slope-
compensation ramp rate (see the Slope Compensation and Current-Sense Resistor section).
Overvoltage Threshold-Adjust Input. Connect a resistor-divider from the switching converter output
to BSTMON and GND. The OVP comparator reference is internally set to 1.23V.
20
21
BSTMON
PGND
Power Ground. PGND is the switching-current return-path connection. Connect GND, LEDGND,
and PGND at a single point.
Switching nMOSFET Gate-Driver Output. Connect NDRV to the gate of the external switching-
power MOSFET. Typically, a small resistor (1Ω to 22Ω) is inserted between the NDRV output and
nMOSFET gate to decrease the slew rate of the gate driver and reduce the switching noise.
22
23
NDRV
VCC
5V Regulator Output. Bypass V
to GND with a minimum of 1μF ceramic capacitor with 22nF in
CC
parallel placed as close as possible to the pin.
www.maximintegrated.com
Maxim Integrated | 14
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Pin Description (continued)
PIN
NAME
FUNCTION
Enable Input. Connect EN to ground to shut down the device. Connect EN to logic-high or IN for
normal operation. EN has an internal clamp at 3.9V. When EN is above this voltage, an input
24
EN
current of (V
- 3.9V)/1.2MΩ will flow.
EN
Exposed Pad. Connect EP to a large-area contiguous copper-ground plane for effective power
dissipation. Do not use as the main IC ground connection. EP must be connected to GND.
-
EP
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Maxim Integrated | 15
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Functional Diagrams
MAX20446B
FLTB
BSTMON
OV
COMP
UV
SHORTGND
VBG
LEDUNUSED
LEDSHORT
LEDOPEN
SHORTGND
UV
FAULT
DETECTOR
FAULT FLAG LOGIC
LEDSHORT
LEDOPEN
TSHDN
LEDUNUSED
UV
COMP
COMP
NDRV
0.4V
VCC
SSDONE
6
g
M
SSDONE
RANGE
PWM
COMP
NDRV
LOGIC
EAREF
$ ARRAY=6
V
THH
6
ORPHASE
BOOSTON
COMPH
RTDET
8
CONTROL
LOGIC
6
UP/DOWN
COUNTER
DAC
OUT_
6
LODIM
V
THL
COMPL
RT
OSCILLATOR
SLOPE
6
IREF_
MAX20446B
POK
CS
COMP
COMPENSATION
CURRENT
IMON_
0.425V
DIMPHASE
6
CS
CS BLANKING
20 MHz
CLOCK
FSEN
RTDET
SHORTGND
LEDSHORT
LEDOPEN
LEDUNUSED
OVPUV
TSHDN
ORPHASE
LODIM
THERMAL
SHUTDOWN
DIM LOGIC &
PHASE SHIFTING
LEDGND
PGATE
PRE-
REGULATOR
BOOSTON
PGATE
CONTROL
BANDGAP
VBG
IN
200 mA
UVLO VIN
8
VINUVLO
ADC
REGISTER
MAP &
SCL
SDA
INTERFACE
IMON
MUX
7:1
5V
REGULATOR
VCC
STMON
ISET[3:0]
TONH[17:0]
UVLO
VVCC
VINUVLO
IN
POK
REFERENCE
CURRENT
GENERATION
IREF_
0
EN
COMP
DUTY-CYCLE
MEASUREMENT
1
DIM
TSHDN
EN
20MHz
DIM_EXT
SHDN
POK
GND
PGND
IREF
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Maxim Integrated | 16
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Detailed Description
The MAX20446B high-efficiency HB LED driver integrates all the necessary features to implement a high-performance
backlight driver to power LEDs in medium-to-large-sized displays for automotive, as well as general, applications. The
device provides load-dump voltage protection up to 52V in automotive applications and incorporates a DC-DC controller
with peak current-mode control to implement a boost or a SEPIC-type switched-mode power supply and a 6-channel
LED driver with 45mA to 130mA constant-current sink capability per channel.
Enable
2
The internal regulator and I C interface are enabled when the EN pin is high if the IN pin voltage is above its undervoltage
lockout. To shut down the device, drive EN low so the current consumption is reduced to 1μA (max).
Undervoltage Lockout
The device features two undervoltage lockouts (UVLOs) that monitor the input voltage at IN and the output of the internal
LDO regulator at V . The device turns on when EN is taken high if both IN and V
are higher than their respective
CC
CC
UVLO thresholds.
Current-Mode DC-DC Controller
The device has a constant-frequency, current-mode controller designed to drive the LEDs in a boost, SEPIC, or coupled-
inductor buck-boost configuration. The device features multiloop control to regulate the peak current in the inductor, as
well as the voltage across the LED current sinks to minimize power dissipation.
The switching frequency can be programmed over the 400kHz to 2.2MHz range using a resistor connected from RT to
GND.
Internal slope compensation is provided to compensate for subharmonic oscillations that occur at above 50% duty cycles
in continuous-conduction mode.
The internal MOSFET is turned on at the beginning of every switching cycle. The inductor current ramps up linearly until
it is turned off at the peak current level set by the feedback loop. The peak inductor current is sensed from the voltage
across the current-sense resistor (R ), connected from the source of the external MOSFET to ground.
CS
The device features leading-edge blanking to suppress the internal MOSFET switching noise. A PWM comparator
compares the current-sense voltage plus the slope-compensation signal with the output of the transconductance error
amplifier. The controller turns off the MOSFET when the voltage at CS exceeds the error amplifier’s output voltage, which
is also the voltage on the COMP pin. This process repeats every switching cycle to achieve peak current-mode control.
In addition to the peak current-mode-control loop, the device has two other feedback loops for control. The converter
output voltage is sensed through the BSTMON input, which goes to the inverting input of the error amplifier. The other
feedback comes from the OUT_ current sinks. This loop controls the headroom of the current sinks to minimize total
power dissipation while still ensuring accurate LED current matching. Each current sink has a window comparator with a
low threshold of 0.78V and a high threshold of 1.03V. The outputs of these comparators control an up/down counter. The
up/down counter is updated on every falling edge of the DIM input and drives an 8-bit DAC that sets the reference to the
error amplifier. When dimming is set to 100%, the counter is updated at intervals of 10ms.
8-Bit Digital-to-Analog Converter
The error amplifier’s reference input is controlled with an 8-bit digital-to-analog converter (DAC). The DAC output ramps
up slowly during startup to implement a soft-start function (see the Startup Sequence section). During normal operation,
the DAC output range is limited to 0.6V to 1.25V. Because the DAC output is limited to no less than 0.6V during normal
operation, the overvoltage threshold for the output should be set to a value less than twice the minimum LED forward
voltage. The DAC LSB determines the minimum step-in output voltage according to Equation 1.
Equation 1:
V
= V
× A
DAC_LSB OVP
STEP_MIN
where:
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Maxim Integrated | 17
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
V
V
A
= Minimum output-voltage step
STEP_MIN
= DAC least significant bit size (2.5mV)
DAC_LSB
= BSTMON resistor-divider gain
OVP
FSEN Pin Function
2
The FSEN (fail-safe enable) pin can be used to enable the device in situations where I C control is temporarily impossible
or the interface has stopped functioning. When FSEN is taken high, the boost converter is turned on and the current sinks
enabled. When FSEN returns low, the values programmed in the I C registers are applied at the beginning of the next
2
dimming cycle.
The OUT_ current when FSEN is high is set by a resistor from FSEN to GND according to Table 1.
Table 1. FSEN Pin Function
FSEN RESISTOR
OUT_ CURRENT
MAX20446BATGA
I C ADDRESS
MAX20446BATG
I C ADDRESS
2
2
VALUE (kΩ)
(mA)
0
Fail-safe disabled
0x61
0x61
0x67
0x61
0x67
0x61
0x67
0x61
0x67
0x63
0x63
0x6B
0x63
0x6B
0x63
0x6B
0x63
0x6B
3.48
7.15
12
25
25
50
18.7
27.4
39
50
75
75
59
100
100
84.5
2
The resistor value is read at power-up; therefore, the set OUT_ current value and I C address cannot be changed after
power-up.
2
If FSEN is not used, connect the pin to GND, unless an I C address other than the default is desired.
Dimming
Dimming can be performed either using an external PWM signal applied to the DIM pin or by programming the desired
2
dimming level through I C.
When using the DIM pin as an input, set the DIM_EXT bit in the IMODE register (0x03) to 1 (this is also the default value).
The signal on the DIM pin is sampled with a 20MHz internal clock.
When using internal dimming, write up to 18 bits to the TON_[17:0] bits. The value to be written is calculated using the
following formula: TON = t /50ns, where t
is the desired on-time. If a value is written that corresponds to an on-time
ON
ON
less than 500ns (≤ 0x09), the corresponding OUT_ stays on for 500ns. To set zero current in any channel, write all the
corresponding TON bits to 0.
Hybrid Dimming
In hybrid dimming mode, the external LEDs are dimmed by first reducing their current as the dimming duty-cycle
decreases from 100% (see Figure 1). At the crossover level set by the HDIM[1:0] bits, dimming transitions to PWM in
which the LED current is chopped. To select hybrid dimming, set the HDIM bit in the IMODE register and select the
desired crossover level between analog and PWM dimming using the HDIM_THR[1:0] bits in the same register (see
Figure 1). Depending on the DIM_EXT bit, one of the following occurs:
● If DIM_EXT = 1, the device measures the duty-cycle on the DIM pin and translates it into a combined LED current
value and PWM setting.
● If DIM_EXT = 0, the device takes the concatenated 18-bit value from the TONH_:TONL_:TON_LSB registers and
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Maxim Integrated | 18
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
translates it into a combined LED current value and PWM setting.
Note: When hybrid dimming is used with an internal dimming setting (e.g., DIM_EXT = 0) only the value in the
TONH_:TONL_ registers is used. It is not possible to have individual dimming settings for each of the channels in this
mode, but the TONH:TONL settings for all the channels must be non-zero.
In summary, there are four possible dimming modes:
● External PWM dimming
2
● Internal PWM dimming with the pulse width set through I C and the PWM frequency generated internally.
● External hybrid dimming with a PWM signal applied to the DIM pin. In this mode the pulsed current on the OUT_ pins
follows the DIM frequency.
2
● Internal hybrid dimming with the dimming ratio set through I C and the PWM frequency generated internally.
Figure 2 illustrates the difference between standard and hybrid dimming with phase shifting enabled.
Hybrid Dimming Operation
ILLUSTRATION OF HYBRID DIMMING OPERATION WITH HDIM[1:0]=10 (25%)
ISET_
CURRENT
ISET_
CURRENT/4
100%
75%
50%
25%
0%
DIM DUTY-CYCLE OR TONH1:TONL1 SETTING
Figure 1. Hybrid Dimming Operation
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Maxim Integrated | 19
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Hybrid Dimming Operation Modes
EXTERNAL PWM DIMMING AT 75%
HYBRID EXTERNAL DIMMING AT 75%
DIM
DIM
75% OF ISET_
CURRENT
OUT1
CURRENT
OUT1
CURRENT
OUT2
CURRENT
OUT2
CURRENT
NOTE: ONLY TWO OF SIX OUTPUT CHANNELS SHOWN
EXTERNAL PWM DIMMING AT 25%
HYBRID EXTERNAL DIMMING AT 25% (HDIM_THR[1:0]=11)
DIM
DIM
OUT1
CURRENT
OUT1
CURRENT
50% OF ISET_
CURRENT
OUT2
CURRENT
OUT2
CURRENT
Figure 2. Hybrid Dimming Operation Modes
Low-Dimming Mode
The device operation changes at very narrow dimming pulses to ensure a consistent dimming response of the LEDs. If
the dimming on-time (either of the DIM input or of the value in the PWM_ bits, depending on which is selected) is lower
than 50μs (typ), the device enters low-dimming mode. In this state, the converter switches continuously and the LED
short detection is disabled. When the DIM input is greater than 51μs (typ), the device goes back into normal operation,
enabling the short-LED detection and switching the power MOSFET only when the effective dimming signal is high. OUT_
current monitoring does not operate in low-dim mode, although the BSTMON voltage can still be measured.
2
When the device is used in I C mode with internal dimming, some channels may be in low-dim mode while others may
not. If any channel is in low-dim mode, the boost converter runs continuously.
Phase-Shift Dimming
When the PSEN bit in the ISET register (0x02) is set, phase shifting of the LED strings is enabled. The device
automatically sets the phase shift between strings to 60, 72, 90, 120, or 180 degrees, depending on the number of strings
enabled.
Disabling Individual Strings
To disable an unused LED string, connect the unused OUT_ to ground through a 12kΩ resistor, or set the corresponding
DIS_ bit to 1 in the DISABLE (0x13) register. During startup, the device sources 60μA (typ) current through the OUT_
pins and measures the corresponding voltage. For the string to be properly disabled, the OUT_ voltage should measure
between 350mV and 1.15V during this check. 350mV is the maximum threshold for the OUT_ short-to-ground check and
1.15V is the minimum unused string-detection threshold.
Note: When disabling unused strings, start by disabling the highest numbered current sinks first (e.g., if two strings need
to be disabled, disable OUT6 and OUT5. Do not disable any two strings at random). During normal operation, strings can
be selectively turned off by changing the corresponding PWM setting to 0. This is only possible when internal dimming is
used (not when using the DIM input pin).
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Maxim Integrated | 20
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Startup Sequence
When the EN pin is taken high (assuming the IN voltage is above its undervoltage-lockout value), the internal regulator
and the interface are turned on and the device checks the OUT_ channels. If any of the OUT_ pins are detected as
shorted to GND, the boost converter will not start (to avoid possible damage) and the corresponding OUTSG bit(s) are
set. The device also detects and disconnects any unused current-sink channels that are connected to GND through a
2
12kΩ resistor. Alternatively, when using the I C interface, individual channels can be disabled using the DIS4:1 bits. The
2
total duration of this phase of the startup is 2ms (max). After this phase, the I C interface can be used and the device
registers written. Finally, the ENA bit is set to 1 to enable the boost and subsequently the OUT_ current sinks. When the
ENA bit is set high, the startup sequence occurs in three stages (see the Stage 1, Stage 2, and Stage 3 sections).
Stage 1
Once the ENA bit is high, the controller begins the soft-start of the boost. First, the driver of the external pMOSFET is
turned on. A constant current of 200μA (typ) then flows into the PGATE pin of the device. This current flows into the
external gate-source resistor and pulls down the gate of the external pMOSFET and turns it on. An external gate-source
capacitor can be used to control the turn-on time of the external pMOSFET.
After the external pMOSFET is turned on and a 2ms timeout expires, Stage 2 of the startup begins (see the Stage 2
section).
Stage 2
After the checks in Stage 1 have been performed, the converter starts switching and the output begins to ramp. The DAC
reference to the error amplifier is stepped up 1 bit at a time until it reaches 600mV (or 1.1V if fast soft start is enabled).
This stage duration is fixed at approximately 50ms (typ) (or 25ms when DIS_FASTSS is set to 0). The BSTMON pin
is then monitored, and if the voltage at the BSTMON pin is less than 500mV (typ), FLTB is asserted low, the power
converter is turned off, the external pMOSFET is turned off, and they all remain off until the ENA bit is toggled (see the
Stage 3 section).
Stage 3
The third stage begins once Stage 2 is complete and the DIM input goes high (with DIM_EXT = 1), or internal dimming
is enabled by setting a PWM value greater than 0 on any of the channels. During Stage 3, the output of the converter
is adjusted until the minimum OUT_ voltage falls within 0.68V (typ) and 0.93V (typ) comparator limits. The output
adjustment is again controlled by the DAC, which provides the reference for the error amplifier. The DAC output is
updated on each rising edge of the DIM input pin (or internal dimming signal). If the DIM input (or the internal dimming
signal when DIM_EXT = 1) is at 100% duty cycle (DIM = high), the DAC output is updated once every 10ms.
The total soft-start time can be calculated using Equation 2.
Equation 2:
(V
+ 0.91) − (0.6 × A
× 0.01 × A
)
LED
OVP
t
= 52ms +
SS
f
DIM
OVP
where:
SS = Total soft-start time
52ms = Fixed Stage 1 + Stage 2 duration (27ms when DIS_FASTSS = 0)
= Total forward voltage of the LED strings
V
LED
0.91V = Midpoint of the window comparator
0.6 = Voltage on BSTMON after Stage 2 (use 1.1 when DIS_FASTSS = 0)
f
= Dimming frequency (use 100Hz for f
when input duty cycle is 100%)
DIM
DIM
0.01V = 4 times the 2.5mV LSB of the DAC
= Gain of the BSTMON resistor-divider or 1 + R6/R7
A
OVP
After the soft-start period, a fault is detected whenever the BSTMON pin falls below 430mV (typ). When this occurs, the
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Maxim Integrated | 21
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
power converter is latched off and PGATE goes high. Cycling the ENA bit or the supply is required to start up again once
the fault condition has been removed.
Figure 3: Boost Startup
EN
V
CC
2ms
OUT_ CHECK
ENA BIT
PGATE
2ms
FINAL BOOST
OUTPUT
50ms
VOLTAGE
BOOST
OUTPUT
~V
IN
BSTMON > 500mV
TEST
NDRV
DIM
Figure 3. Boost Startup with DIS_FASTSS = 1
Oscillator Frequency/External Synchronization
The internal oscillator frequency is programmable between 400kHz and 2.2MHz using a timing resistor (R ) connected
RT
from the RT pin to GND. Use Equation 3 to calculate the value of R for the desired switching frequency (f ).
RT
SW
Equation 3:
29260 + (2200 − f
) × 0.81
SW
R
=
RT
f
SW
where f
is in kHz and R is in kΩ.
RT
SW
Synchronize the oscillator with an external clock by AC-coupling the external clock to the RT input. The value of the
capacitor used for AC-coupling is C
= 10pF and the duty cycle of the external clock should be 50%.
SYNC
Spread-Spectrum Mode
The device includes a spread-spectrum mode that reduces peak electromagnetic interference (EMI) at the switching
frequency and its harmonics.
The spread spectrum uses a pseudorandom dithering technique where the switching frequency is varied in the range of
97% (or 94% when the SSL bit is 1) of the programmed switching frequency, to 103% (or 106% when the SSL bit is 1) of
the programmed switching frequency set through the external resistor from RT to GND. When spread spectrum is used,
the total energy at the fundamental and each harmonic is spread over a wider bandwidth, reducing the energy peak.
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Maxim Integrated | 22
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Spread spectrum is disabled if external synchronization is used. Optionally, spread spectrum can be disabled by setting
the SS_OFF bit in the SETTING register to 1. The amount of spread spectrum can also be varied between ±3% and ±6%
using the SSL bit in the same register.
5V LDO Regulator (V
)
CC
The internal LDO regulator converts the input voltage at IN to a 5V output voltage at V . The LDO regulator supplies up
CC
to 50mA current to provide power to internal control circuitry and the gate driver. Bypass V
of 1μF (+22nF in parallel) ceramic capacitor, as close as possible to the device.
to GND, with a minimum
CC
LED Current Control
The full-scale sink current for the outputs OUT1–OUT6 is set using the four bits ISET3:0 in register 0x01. See the ISET
(0x02) section to find the correct bit value for the desired current. When PWM dimming is used, the current in the OUT_
channels switches between zero and the full-scale sink current at the set duty cycle.
When hybrid dimming is used, the sink current in OUT1–OUT6 is reduced linearly from the full-scale value until the level
set by HDIM_THR[1:0] is reached; dimming at lower levels is then accomplished using PWM (see Figure 1).
If 130mA current is desired, the resistor on IREF should be changed to 45.3kΩ.
Fault Protection
Fault protection in the device includes cycle-by-cycle current limiting using the PWM controller, DC-DC converter output
undervoltage protection, output overvoltage protection, open-LED detection, short-LED detection and protection, and
overtemperature shutdown. An open-drain fault flag output (FLTB) goes low when an open-LED string is detected, a
short-LED string is detected, during an output undervoltage, or during thermal shutdown. FLTB is cleared when the fault
condition is removed during thermal shutdown and shorted LED detection. FLTB is latched low for an open LED and can
be reset by cycling device power. The thermal-shutdown threshold is +165°C and has +15°C hysteresis.
Open-LED Management and Overvoltage Protection
On power-up, the device performs a soft-start of the boost converter. After soft-start, the device detects open-LED and
disconnects any strings with an open LED from the internal minimum OUT_ voltage detector. This keeps the DC-DC
converter output voltage within safe limits and maintains high efficiency. The current in strings that have been detected
open is not measured and reads as zero.
During normal operation, the DC-DC converter output-regulation loop uses the minimum OUT_ voltage as the feedback
input. If any LED string is open, the voltage at the opened OUT_ goes to V
. The DC-DC converter output
LEDGND
voltage then increases to the overvoltage-protection threshold set by the voltage-divider network connected between the
converter output, the BSTMON input, and GND. The overvoltage-protection threshold at the DC-DC converter output is
determined using Equation 4.
Equation 4:
R6
R7
V
= 1.23 × 1 +
(
OUT_BSTMON
)
where 1.23 (typ) is the overvoltage threshold on BSTMON (see Functional Diagrams). Select V
according
OUT_BSTMON
to Equation 5.
Equation 5:
1.1 × V
+ 1.1 < V
< 2 × V
+ 0.7
(
)
(
)
LED_MAX
OUT_BSTMON
LED_MIN
where:
V
V
= Maximum expected LED string voltage, and
= Minimum expected LED string voltage.
LED_MAX
LED_MIN
Select R6 and R7 such that the voltage at OUT_ does not exceed the Absolute Maximum Ratings. As soon as the DC-
DC converter output reaches the overvoltage-protection threshold, the internal MOSFET is switched off.
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Maxim Integrated | 23
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
The overvoltage threshold should be set less than twice the minimum LED voltage to ensure proper operation; the
BSTMON minimum regulation point is 600mV (typ). Connect a 12kΩ resistor between OUT_ and LEDGND for each
unused channel to avoid overvoltage triggering at startup. When an open-LED overvoltage condition occurs, FLTB is
latched low. Any current-sink output with V
< 300mV (typ) is disconnected from the minimum voltage detector.
OUT_
Short-LED Detection
The device checks for shorted LEDs before the current in any channel is turned on. A shorted LED is detected at OUT_
if the condition in Equation 6 is met.
Equation 6:
V
> RSDT
OUT_
where:
RSDT = Programmable short-LED detection threshold set by the SLDET[2:0] bits in the SETTING (0x12) register.
If a short is detected on any of the strings, the affected LED strings are disconnected and the FLTB output flag asserts
until the device detects that the shorts are removed. Disable short-LED detection by setting SLDET[2:0] to 0. Short-LED
detection is disabled in low-dimming mode. In external dimming mode with the DIM input connected continuously high,
the OUT_ pins are periodically scanned to detect shorted LEDs. The scan frequency is 100Hz.
Similarly when DIM_EXT = 0 and internal dimming is being used, shorted LEDs are still detected by periodically scanning
the OUT_ states.
Thermal Warning/Shutdown
The device includes thermal protection that operates at a temperature of 165°C. When the thermal-shutdown
temperature is reached, the device is immediately disabled and begins to cool. When the junction temperature falls by
15°C, the device is re-enabled with the same settings as before (the boost converter performs a soft-start). When a
2
thermal shutdown occurs, the FLTB pin goes low and the OT bit, if read through I C, is set to 1.
A thermal-warning bit (OTW) implemented in register 0x1F, indicates when the junction temperature has exceeded
125°C. The OTWMASK bit in register 0x1E is used to control whether or not an active OTW bit causes the FLTB pin to
go low.
Analog-to-Digital Converter
The analog-to-digital converter (ADC) is used to measure the current in each of the strings and the voltage on the
BSTMON pin. A conversion cycle is started by setting the CONVERT bit to 1. At the end of the cycle, the CONVERT
bit is reset to 0 to indicate a complete cycle and the IOUT1–OUT6 and BSTMON registers contain the updated values.
The full-scale value of the current measurement is 127.5mA. Values higher than 127.5mA read as full-scale or 0xFF.
Current measurements are not performed on channels that are in low-dim mode; before performing a conversion, this
can be checked by reading the LoDIM_ bits. If a conversion is attempted on a channel that is in low-dim mode, the current
value returned will be 0x00. The duration of a complete conversion depends on whether or not phase shifting is enabled.
With phase shifting enabled, a complete conversion can take up to two dimming cycles (worst case). With phase shifting
disabled, one dimming cycle is the worst-case latency (the conversion is initiated at the beginning of a DIM cycle and is
concluded < 50μs later).
2
I C Interface
2
The IC features an I C, 2-wire serial interface consisting of a serial-data line (SDA) and a serial-clock line (SCL). SDA
and SCL facilitate communication between the device and the master at clock rates up to 400kHz. The master, typically
a microcontroller, generates SCL and initiates data transfer on the bus.
2
The slave address is chosen by connecting the FSEN pin to GND via a resistor, the value of which determines the I C
2
address (see also FSEN Pin Function). Table 2 shows the possible I C addresses.
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Maxim Integrated | 24
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
2
Table 2. I C Address Options
DEVICE ADDRESS
WRITE
ADDRESS ADDRESS
READ
DEVICE
FSEN
7-BIT ADDRESS
A6 A5 A4 A3 A2 A1 A0
MAX20446BATG
MAX20446BATG
0, 3.48k, 12k, 27.4k, 59k
7.15k, 18.7k, 39k, 84.5k
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
1
0
1
0
0
0
1
1
1
1
1
1
1
0xC6
0xD6
0xC2
0xCE
0xC7
0xD7
0xC3
0xCF
0x63
0x6B
0x61
0x67
MAX20446BATGA 0, 3.48k, 12k, 27.4k, 59k
MAX20446BATGA 7.15k, 18.7k, 39k, 84.5k
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Maxim Integrated | 25
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Register Map
MAX20446B
ADDRESS
I2C
NAME
MSB
LSB
0x00
0x01
Dev_ID[7:0]
Rev_ID[7:0]
Device_ID[7:0]
–
–
–
LoDIM6
ENA
LoDIM5
PSEN
Revision_ID[3:0]
ISET[3:0]
CONVE
RT
0x02
0x03
ISET[7:0]
DIM_EX
T
IMODE[7:0]
LoDIM4
LoDIM3
LoDIM2
LoDIM1
HDIM
HDIM_THR[1:0]
0x04
0x05
0x06
0x07
0x08
0x09
0x0A
0x0B
0x0C
0x0D
0x0E
0x0F
0x10
0x11
0x12
TONH1[7:0]
TONL1[7:0]
TONH2[7:0]
TONL2[7:0]
TONH3[7:0]
TONL3[7:0]
TONH4[7:0]
TONL4[7:0]
TON1-4LSB[7:0]
TONH5[7:0]
TONL5[7:0]
TONH6[7:0]
TONL6[7:0]
TON5-6LSB[7:0]
SETTING[7:0]
PWM1[17:10]
PWM1[9:2]
PWM2[17:10]
PWM2[9:2]
PWM3[17:10]
PWM3[9:2]
PWM4[17:10]
PWM4[9:2]
PWM4[1:0]
PWM3[1:0]
PWM2[1:0]
PWM1[1:0]
PWM5[17:10]
PWM5[9:2]
PWM6[17:10]
PWM6[9:2]
–
–
–
–
–
PWM6[1:0]
PWM5[1:0]
SLDET[1:0]
FPWM[2:0]
SS_OFF
DIS4
SSL
DIS_FAS
TSS
0x13
DISABLE[7:0]
–
DIS6
DIS5
DIS3
DIS2
DIS1
0x14
0x15
0x16
0x17
0x18
0x19
0x1A
0x1B
0x1C
0x1D
BSTMON[7:0]
IOUT1[7:0]
VMON[7:0]
IOUT1[7:0]
IOUT2[7:0]
IOUT3[7:0]
IOUT4[7:0]
IOUT5[7:0]
IOUT6[7:0]
IOUT2[7:0]
IOUT3[7:0]
IOUT4[7:0]
IOUT5[7:0]
IOUT6[7:0]
OPEN[7:0]
–
–
–
–
–
–
OUT6O
OUT5O
OUT4O
OUT3O
OUT2O
OUT1O
SHORTGND[7:0]
SHORTED LED[7:0]
OUT6SG OUT5SG OUT4SG OUT3SG OUT2SG OUT1SG
OUT6SL OUT5SL OUT4SL OUT3SL OUT2SL OUT1SL
BSTUVM
ASK
SGMAS OTWMA
0x1E
0x1F
MASK[7:0]
DIAG[7:0]
–
–
–
–
–
OMASK
BSTOV
SLMASK
OT
K
SK
IREFOO
R
HW_RS
T
BSTUV
OTW
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Maxim Integrated | 26
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Register Details
Dev_ID (0x00)
BIT
Field
7
6
5
4
3
2
1
0
Device_ID[7:0]
Reset
0x6B
Access
Type
Read Only
BITFIELD
BITS
DESCRIPTION
DECODE
Device ID, reads 0x6B
Device_ID
7:0
Rev_ID (0x01)
BIT
Field
7
–
–
6
–
–
5
4
3
2
1
0
LoDIM6
LoDIM5
Revision_ID[3:0]
0x1
Reset
Access
Type
–
–
Read Only
Read Only
Read Only
BITFIELD
LoDIM6
BITS
5
DESCRIPTION
When 1, indicates that channel 6 is in low-dim mode.
When 1, indicates that channel 5 is in low-dim mode.
Device revision ID
LoDIM5
4
Revision_ID
3:0
ISET (0x02)
Boost slew rate and output-current setting.
BIT
7
–
–
6
5
4
3
2
1
0
Field
CONVERT
0b0
ENA
0b0
PSEN
0b1
ISET[3:0]
0b1011
Reset
Access
Type
–
Write, Read Write, Read Write, Read
Write, Read
BITFIELD
BITS
DESCRIPTION
Write a 1 to this bit to start a conversion cycle of the ADC. When the cycle is
finished this bit is automatically reset to indicate that data is ready.
CONVERT
6
Table 3.
ENA
ENABLE BIT
ENA
5
4
0
1
Boost converter and LED outputs off
Boost converter and LED outputs on
PSEN
When 0 phase-shifting is disabled. Default value 1.
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Maxim Integrated | 27
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
BITFIELD
BITS
DESCRIPTION
Table 4. LED Current Setting
ISET3
ISET2
ISET1
ISET0
Current Setting
45mA
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
50mA
55mA
60mA
65mA
70mA
75mA
ISET
3:0
80mA
85mA
90mA
95mA
100mA*
105mA
110mA
115mA
120mA
*default value
IMODE (0x03)
Phase-shift enable, individual string disable, analog dimming enable, and setting of crossover between analog/digital
dimming (50%, 25%, 12.5%, 6.25%).
BIT
7
6
5
4
3
2
1
0
Field
LoDIM4
0x0
LoDIM3
0x0
LoDIM2
0x0
LoDIM1
0x0
DIM_EXT
0b1
HDIM
0b0
HDIM_THR[1:0]
0b00
Reset
Access
Type
Read Only
Read Only
Read Only
Read Only
Write, Read Write, Read
Write, Read
BITFIELD
BITS
DESCRIPTION
DECODE
When 1, indicates that channel 4 is in low-dim
mode.
LoDIM4
7
When 1, indicates that channel 3 is in low-dim
mode.
LoDIM3
LoDIM2
LoDIM1
6
5
4
When 1, indicates that channel 2 is in low-dim
mode.
When 1, indicates that channel 1 is in low-dim
mode.
When 1, dimming through the DIM pin is
enabled. When 0, dimming is controlled using
the PWM_ registers. Default value is 1.
DIM_EXT
HDIM
3
2
When 1, hybrid dimming is enabled. Default
value 0.
When 1, hybrid dimming is enabled. Default value
0.
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Maxim Integrated | 28
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
BITFIELD
BITS
DESCRIPTION
DECODE
Set hybrid dimming threshold. Default value
is 6.25% (00).
HDIM_THR
1:0
TONH1 (0x04)
On-time setting for channel 1 with 50ns resolution, high byte.
BIT
7
6
5
4
3
2
1
0
0
0
0
Field
PWM1[17:10]
Reset
0b11111111
Write, Read
Access
Type
BITFIELD
BITS
DESCRIPTION
PWM1
7:0
High byte of 16-bit PWM setting for channel 1.
TONL1 (0x05)
On-time setting for channel 1 with 50ns resolution, low byte.
BIT
7
6
5
4
3
2
1
1
1
Field
PWM1[9:2]
Reset
0b11111111
Access
Type
Write, Read
BITFIELD
BITS
DESCRIPTION
PWM1
7:0
Middle byte of 18-bit PWM setting for channel 1.
TONH2 (0x06)
On-time setting for channel 2 with 50ns resolution2, high byte
BIT
7
6
5
4
3
2
Field
PWM2[17:10]
Reset
0b11111111
Write, Read
Access
Type
BITFIELD
BITS
DESCRIPTION
PWM2
7:0
High byte of 16-bit PWM setting for channel 2.
TONL2 (0x07)
On-time setting for channel 2 with 50ns resolution, low byte.
BIT
7
6
5
4
3
2
Field
PWM2[9:2]
Reset
0b11111111
Access
Type
Write, Read
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Maxim Integrated | 29
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
BITFIELD
BITS
DESCRIPTION
PWM2
7:0
Middle byte of 18-bit PWM setting for channel 2.
TONH3 (0x08)
On-time setting for channel 3 with 50ns resolution, high byte.
BIT
7
6
5
4
3
2
1
1
1
1
0
0
0
0
Field
PWM3[17:10]
Reset
0b11111111
Write, Read
Access
Type
BITFIELD
BITS
DESCRIPTION
PWM3
7:0
High byte of 16-bit PWM setting for channel 3.
TONL3 (0x09)
On-time setting for channel 3 with 50ns resolution, low byte.
BIT
7
6
5
4
3
2
Field
PWM3[9:2]
Reset
0b11111111
Access
Type
Write, Read
BITFIELD
BITS
DESCRIPTION
PWM3
7:0
Middle byte of 18-bit PWM setting for channel 3.
TONH4 (0x0A)
On-time setting for channel 4 with 50ns resolution, high byte.
BIT
7
6
5
4
3
2
Field
PWM4[17:10]
Reset
0b11111111
Write, Read
Access
Type
BITFIELD
BITS
DESCRIPTION
PWM4
7:0
High byte of 16-bit PWM setting for channel 4.
TONL4 (0x0B)
On-time setting for channel 4 with 50ns resolution, low byte.
BIT
7
6
5
4
3
2
Field
PWM4[9:2]
Reset
0b11111111
Access
Type
Write, Read
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Maxim Integrated | 30
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
BITFIELD
BITS
DESCRIPTION
PWM4
7:0
Middle byte of 18-bit PWM setting for channel 4.
TON1-4LSB (0x0C)
–
BIT
7
6
5
4
3
2
1
0
Field
PWM4[1:0]
0b11
PWM3[1:0]
0b11
PWM2[1:0]
0b11
PWM1[1:0]
0b11
Reset
Access
Type
Write, Read
Write, Read
Write, Read
Write, Read
BITFIELD
BITS
7:6
DESCRIPTION
PWM4
PWM3
PWM2
PWM1
2 least significant bits of 18-bit PWM setting for channel 4.
2 least significant bits of 18-bit PWM setting for channel 3.
2 least significant bits of 18-bit PWM setting for channel 2.
2 least significant bits of 18-bit PWM setting for channel 1.
5:4
3:2
1:0
TONH5 (0x0D)
On-time setting for channel 5 with 50ns resolution, high byte.
BIT
7
6
5
4
3
2
1
0
Field
PWM5[17:10]
Reset
0xFF
Access
Type
Write, Read
BITFIELD
BITS
DESCRIPTION
PWM5
7:0
High byte of 16-bit PWM setting for channel 5.
TONL5 (0x0E)
On-time setting for channel 5 with 50ns resolution, low byte.
BIT
7
6
5
4
3
2
1
0
Field
PWM5[9:2]
Reset
0b11111111
Access
Type
Write, Read
BITFIELD
BITS
DESCRIPTION
PWM5
7:0
Middle byte of 18-bit PWM setting for channel 5.
TONH6 (0x0F)
On-time setting for channel 6 with 50ns resolution, high byte.
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Maxim Integrated | 31
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
BIT
Field
7
6
5
4
3
2
1
1
1
0
0
0
PWM6[17:10]
Reset
0b11111111
Write, Read
Access
Type
BITFIELD
BITS
DESCRIPTION
PWM6
7:0
High byte of 16-bit PWM setting for channel 6.
TONL6 (0x10)
On-time setting for channel 6 with 50ns resolution, low byte.
BIT
7
6
5
4
3
2
Field
PWM6[9:2]
Reset
0b11111111
Access
Type
Write, Read
BITFIELD
BITS
DESCRIPTION
PWM6
7:0
Middle byte of 18-bit PWM setting for channel 6.
TON5-6LSB (0x11)
–
BIT
7
6
–
–
5
–
–
4
–
–
3
2
Field
–
–
PWM6[1:0]
0b11
PWM5[1:0]
0b11
Reset
Access
Type
–
–
–
–
Write, Read
Write, Read
BITFIELD
BITS
3:2
DESCRIPTION
PWM6
PWM5
2 least significant bits of 18-bit PWM setting for channel 6.
2 least significant bits of 18-bit PWM setting for channel 5.
1:0
SETTING (0x12)
External/internal dimming, DIM-frequency level for shorted-LED detection.
BIT
7
–
–
6
5
4
3
2
1
0
Field
FPWM[2:0]
0b001
SS_OFF
0b0
SSL
0b0
SLDET[1:0]
000
Reset
Access
Type
–
Write, Read
Write, Read Write, Read
Write, Read
BITFIELD
BITS
6:4
3
DESCRIPTION
These bits set the PWM frequency in internal PWM mode. When an external
DIM signal is used, these bits set the fault-sampling frequency at 100% duty
cycle.
FPWM
SS_OFF
When 1 spread-spectrum switching is disabled. Default value 0.
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Maxim Integrated | 32
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
BITFIELD
BITS
DESCRIPTION
When spread-spectrum is enabled the SSL bit chooses the amount of spread:
when 0 the spread is nominally ±6%, when 1 ±3%.
SSL
2
SLDET1
SLDET0
SETTING
Disabled
3V
0
0
1
1
0
1
0
1
SLDET
1:0
6V
8V
Shorted-LED Threshold Setting:
DISABLE (0x13)
BIT
Field
7
–
–
–
6
5
4
3
2
1
0
DIS_FASTS
S
DIS6
0b0
DIS5
0b0
DIS4
0b0
DIS3
0b0
DIS2
0b0
DIS1
0b0
Reset
0x0
Access
Type
Write, Read Write, Read Write, Read Write, Read Write, Read Write, Read Write, Read
BITFIELD
BITS
DESCRIPTION
DIS_FASTSS
6
Selects fast or slow boost soft-start. Set to 1 for slow soft-start.
Set this bit to 1 to disable OUT6. This must be done before ENA is written to
1.
DIS6
DIS5
DIS4
DIS3
DIS2
DIS1
5
4
3
2
1
0
Set this bit to 1 to disable OUT5. This must be done before ENA is written to
1.
Set this bit to 1 to disable OUT4. This must be done before ENA is written to
1.
Set this bit to 1 to disable OUT3. This must be done before ENA is written to
1.
Set this bit to 1 to disable OUT2. This must be done before ENA is written to
1.
Set this bit to 1 to disable OUT1. This must be done before ENA is written to
1.
BSTMON (0x14)
BSTMON pin voltage readback.
BIT
7
6
5
4
3
2
1
0
Field
VMON[7:0]
Reset
0b00000000
Access
Type
Read Only
BITFIELD
BITS
DESCRIPTION
VMON
7:0
Voltage on BSTMON. Full-scale = 2.5V.
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Maxim Integrated | 33
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
IOUT1 (0x15)
OUT1 current readback.
BIT
7
6
5
4
3
2
1
0
Field
IOUT1[7:0]
Reset
0b00000000
Access
Type
Read Only
BITFIELD
BITS
DESCRIPTION
Table 5. Output Current Measurement (IOUT1):
READOUT
0x00
CURRENT (mA)
0
0.5
0x01
IOUT1
7:0
…
…
0xFE
0xFF
127
127.5
IOUT2 (0x16)
OUT2 current readback.
BIT
7
6
5
4
3
2
1
0
Field
IOUT2[7:0]
Reset
Access
Type
Read Only
BITFIELD
BITS
DESCRIPTION
Output Current Measurement (IOUT2):
READOUT
CURRENT (mA)
0x00
0x01
...
0
0.5
...
IOUT2
7:0
0xFE
0xFF
127
127.5
IOUT3 (0x17)
OUT3 current readback
BIT
7
6
5
4
3
2
1
0
Field
IOUT3[7:0]
Read Only
Reset
Access
Type
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Maxim Integrated | 34
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
BITFIELD
BITS
DESCRIPTION
Output Current Measurement (IOUT3):
READOUT
CURRENT (mA)
0x00
0x01
...
0
0.5
...
IOUT3
7:0
0xFE
0xFF
127
127.5
IOUT4 (0x18)
OUT4 current readback.
BIT
7
6
5
4
3
2
1
0
Field
IOUT4[7:0]
Reset
0b00000000
Read Only
Access
Type
BITFIELD
BITS
DESCRIPTION
Table 6. Output Current Measurement (IOUT4):
READOUT
0x00
CURRENT (mA)
0
0.5
0x01
IOUT4
7:0
…
…
0xFE
0xFF
127
127.5
IOUT5 (0x19)
OUT5 current readback.
BIT
7
6
5
4
3
2
1
0
Field
IOUT5[7:0]
Reset
0b00000000
Read Only
Access
Type
BITFIELD
BITS
DESCRIPTION
Table 7. Output Current Measurement (IOUT5):
READOUT
0x00
CURRENT (mA)
0
0.5
0x01
IOUT5
7:0
…
…
0xFE
0xFF
127
127.5
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Maxim Integrated | 35
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
IOUT6 (0x1A)
OUT6 current readback.
BIT
7
6
5
4
3
2
1
0
Field
IOUT6[7:0]
Reset
0b00000000
Access
Type
Read Only
BITFIELD
BITS
DESCRIPTION
Table 8. Output Current Measurement (IOUT6):
READOUT
0x00
CURRENT (mA)
0
0.5
0x01
IOUT6
7:0
…
…
0xFE
0xFF
127
127.5
OPEN (0x1B)
Short-to-GND and open diagnostics.
BIT
7
–
–
6
–
–
5
4
3
2
1
0
Field
OUT6O
0x0
OUT5O
0b0
OUT4O
0b0
OUT3O
0b0
OUT2O
0b0
OUT1O
0b0
Reset
Access
Type
–
–
Read Only
Read Only
Read Only
Read Only
Read Only
Read Only
BITFIELD
BITS
DESCRIPTION
OUT6O
OUT5O
OUT4O
OUT3O
OUT2O
OUT1O
5
4
3
2
1
0
If 1, an open has been detected on channel 6.
If 1, an open has been detected on channel 5.
If 1, an open has been detected on channel 4.
If 1, an open has been detected on channel 3.
If 1, an open has been detected on channel 2.
If 1, an open has been detected on channel 1.
SHORTGND (0x1C)
BIT
Field
7
–
–
6
–
–
5
4
3
2
1
0
OUT6SG
OUT5SG
OUT4SG
OUT3SG
OUT2SG
OUT1SG
Reset
Access
Type
–
–
Read Only
Read Only
Read Only
Read Only
Read Only
Read Only
BITFIELD
BITS
DESCRIPTION
OUT6SG
OUT5SG
OUT4SG
5
4
3
If 1, a short-to-ground has been detected on channel 6 at startup.
If 1, a short-to-ground has been detected on channel 5 at startup.
If 1, a short-to-ground has been detected on channel 4 at startup.
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Maxim Integrated | 36
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
BITFIELD
OUT3SG
BITS
DESCRIPTION
2
1
0
If 1, a short-to-ground has been detected on channel 3 at startup.
If 1, a short-to-ground has been detected on channel 2 at startup.
If 1, a short-to-ground has been detected on channel 1 at startup.
OUT2SG
OUT1SG
SHORTED LED (0x1D)
Shorted-LED diagnostics.
BIT
7
–
–
6
–
–
5
4
3
2
1
0
Field
OUT6SL
0b0
OUT5SL
0b0
OUT4SL
0b0
OUT3SL
0b0
OUT2SL
0b0
OUT1SL
0b0
Reset
Access
Type
–
–
Read Only
Read Only
Read Only
Read Only
Read Only
Read Only
BITFIELD
BITS
DESCRIPTION
OUT6SL
OUT5SL
OUT4SL
OUT3SL
OUT2SL
OUT1SL
5
4
3
2
1
0
If 1, a shorted-LED condition has been detected on channel 6.
If 1, a shorted-LED condition has been detected on channel 5.
If 1. a shorted-LED condition has been detected on channel 4.
If 1, a shorted-LED condition has been detected on channel 3.
If 1, a shorted-LED condition has been detected on channel 2.
If 1, a shorted-LED condition has been detected on channel 1.
MASK (0x1E)
Mask register for FLTB pin.
BIT
7
–
–
–
6
–
–
–
5
–
–
–
4
3
2
1
0
BSTUVMAS
K
Field
OMASK
0b0
SGMASK
0b0
OTWMASK
0b0
SLMASK
0b0
Reset
0b0
Access
Type
Write, Read Write, Read Write, Read Write, Read Write, Read
BITFIELD
BITS
DESCRIPTION
When 1 a boost fault (undervoltage or overvoltage) does not cause the FLT
pin to assert low.
BSTUVMASK
4
OMASK
3
2
When 1 an open-LED fault does not cause the FLT pin to assert low.
SGMASK
When 1 a short-to-ground LED fault does not cause the FLT pin to assert low.
When 1 an over-temperature warning does not cause the FLT pin to assert
low.
OTWMASK
SLMASK
1
0
When 1 a shorted-LED fault does not cause the FLT pin to assert low.
DIAG (0x1F)
Boost state, over-temperature warning/shutdown.
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Maxim Integrated | 37
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
BIT
Field
7
–
–
6
–
–
5
4
3
2
1
0
IREFOOR
0b0
BSTUV
0b0
BSTOV
0b0
HW_RST
0b1
OTW
OT
0b0
Reset
Access
Type
–
–
Read Only
Read Only
Read Only
Read Only
Read Only
Read Only
BITFIELD
BITS
DESCRIPTION
When 1, this bit indicates that the IREF current is out of range. This is
probably due to an incorrect resistor value on IREF. In this condition, the IC
stops operation.
IREFOOR
5
If 1, an undervoltage has been detected on the boost output and the boost
was disabled.
BSTUV
BSTOV
HW_RST
OTW
4
3
2
1
0
If 1, the boost converter is at its overvoltage limit.
If 1, the device has just emerged from a hardware reset (power-up). This bit is
reset after the first read from this register.
If 1, the junction temperature of the device is over 125°C.
If 1, the junction temperature of the device exceeded 165°C and the device
was shut down.
OT
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Maxim Integrated | 38
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Applications Information
DC-DC Converter
Three different converter topologies are possible with the DC-DC converter in the MAX20446B, which have the ground-
referenced outputs necessary to use the constant-current sink drivers. If the LED string forward voltage is always greater
than the input supply voltage range, use the boost converter topology. If the LED string forward voltage falls within the
supply voltage range, use a buck-boost converter topology. The possible buck-boost topologies are SEPIC or a coupled-
inductor buck-boost topology. The latter is basically a flyback converter with 1:1 turns ratio. 1:1-coupled inductors are
available with tight coupling suitable for this application.
The boost-converter topology provides the highest efficiency among the above-mentioned topologies. The coupled-
inductor topology has the advantage of not using a coupling capacitor, but does require tightly coupled windings to avoid
additional snubber components. The SEPIC configuration requires two inductors (or a coupled inductor) and a coupling
capacitor. Furthermore, the feedback-loop compensation for SEPIC becomes complex if the coupling capacitor is not
large enough.
Power-Circuit Design
First, select a converter topology based on the factors listed in the DC-DC Converter section. Determine the required
input supply voltage range, the maximum voltage needed to drive the LED strings, including the minimum 0.85V across
the constant LED current sink (V
Equation 7.
), and the total output current needed to drive the LED strings (I
), as shown in
LED
LED
Equation 7:
I
= I
× N
STRING STRING
LED
where I
is the current per string and N
is the number of strings used.
) using Equations 8 and 9.
STRING
STRING
Next, calculate the maximum duty cycle (D
MAX
For boost configuration (Equation 8):
V
+ V − V
D1
(
(
)
)
LED
IN_MIN
D
=
MAX
V
+ V − V
− 0.3
LED
D1
DS
For SEPIC and coupled-inductor buck-boost configurations (Equation 9):
V
+ V
LED
D1
D
=
MAX
V
− V
DS
− 0.3 + V + V
LED D1
(
)
IN_MIN
where:
● V = Forward drop of the rectifier diode in volts (approximately 0.6V),
D1
● V
● V
= Minimum input supply voltage, and
= Drain-to-source voltage of the external MOSFET when it is on.
IN_MIN
DS
Select the switching frequency (f ) depending on the space, noise, and efficiency constraints.
SW
Boost and Coupled-Inductor Configurations
In all three converter configurations, the average inductor current varies with the line voltage; the maximum average
current occurs at the lowest line voltage. For the boost converter, the average inductor current is equal to the input
current. Select the maximum peak-to-peak ripple on the inductor current (ΔI ). The recommended maximum peak-to-
L
peak ripple is 60% of the average inductor current, but lower and higher values for ripple are also acceptable.
Use the following equations (Equations 10, 11, and 12) to calculate the maximum average inductor current (I
) and
LAVG
peak inductor current (I ) in amperes.
LP
Equation 10:
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Maxim Integrated | 39
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
I
LED
I
=
LAVG
1 − D
(
)
MAX
Allowing the peak-to-peak inductor ripple ΔI to be ±30% of the average inductor current:
L
Equation 11:
ΔI = I
× 0.3 × 2
LAVG
L
and:
ΔI
L
I
= I
+
LAVG
2
LP
Calculate the minimum inductance value (L
), in henries (H), with the inductor current ripple set to the maximum value:
MIN
Equation 12:
V
− V
− 0.3 × D
(
)
IN_MIN
DS
MAX
L
=
MIN
f
× ΔI
SW
L
Choose an inductor that has a minimum inductance greater than the calculated L
and current rating greater than I
.
LP
MIN
The recommended saturation current limit of the selected inductor is 10% higher than the inductor peak current for boost
configuration. For the coupled-inductor, the saturation limit of the inductor with only one winding conducting should be
10% higher than I
.
LP
SEPIC Configuration
Power-circuit design for the SEPIC configuration is very similar to a conventional design with the output voltage
referenced to the input supply voltage. For SEPIC, the output is referenced to ground and the inductor is split into two
parts. One of the inductors (L2) takes LED current as the average current and the other (L1) takes input current as the
average current.
Use the following equations (Equations 13–16) to calculate the average inductor currents (I
, I
) and peak
L1AVG L2AVG
inductor currents (I
, I
) in amperes.
L1P L2P
Equation 13:
I
× D
MAX
× 1.1
LED
I
=
L1AVG
1 − D
MAX
The factor 1.1 provides a 10% margin to account for the converter losses.
Equation 14:
I
= I
LED
L2AVG
Assuming the peak-to-peak inductor ripple ΔI is ±30% of the average inductor current
L
Equation 15:
ΔI = I
× 0.3 × 2
L1
L1AVG
and:
ΔI
L1
I
= I
+
L1P
L1AVG
2
and:
ΔI = I
× 0.3 × 0.2
L2AVG
L2
and:
ΔI
L2
I
= I
+
L2AVG
L2P
2
Calculate the minimum inductance values (L1
and L2
) in henries with the inductor current ripple set to the
MIN
MIN
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Maxim Integrated | 40
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
maximum value shown in Equation 16.
Equation 16:
V
V
− V
− 0.3 × D
(
(
)
IN_MIN
IN_MIN
DS
MAX
L1
L2
=
=
MIN
MIN
f
× ΔI
SW
L1
− V
− 0.3 × D
)
DS
MAX
f
× ΔI
SW
L2
Choose inductors that have a minimum inductance greater than the calculated L1
and L2
, and current rating
MIN
MIN
greater than I
and I
, respectively. The recommended saturation current limit of the selected inductor is 10% higher
L1P
L2P
than the inductor peak current.
To simplify further calculations, consider L1 and L2 as a single inductor with L1 and L2 connected in parallel. The
combined inductance value and current is calculated as shown in Equation 17.
Equation 17:
L1 × L2
L =
L1 + L2
and:
I
= I
+ I
L1AVG L2AVG
LAVG
where I
represents the total average current through both the inductors in the SEPIC configuration. Use these
LAVG
values in the calculations in the following sections.
Select coupling-capacitor C so that the peak-to-peak ripple on it is less than 2% of the minimum input supply voltage.
S
This ensures that the second-order effects created by the series-resonant circuit comprising L1, C , and L2 do not affect
S
the normal operation of the converter. Use Equation18 to calculate the minimum value of C :
S
Equation 18:
I
× D
LED
IN_MIN
MAX
× 0.02 × f
C =
S
V
SW
where:
● C = Minimum value of the coupling capacitor in farads, and
S
● 0.02 = 2% ripple factor.
Slope Compensation and Current-Sense Resistor
The device generates a current ramp for slope compensation. This ramp current is in sync with the switching frequency
and starts from zero at the beginning of every clock cycle, rising linearly to reach 50μA at the end of the clock cycle.
The slope-compensating resistor (R ) is connected between the CS input and the source of the external switching
SC
MOSFET. This adds a programmable ramp voltage to the CS input voltage to provide slope compensation.
Use one of the the following equations (Equation 19 or 20) to calculate the value of R
.
SC
For boost configuration (Equation 19):
(V
− 2 × V
IN_MIN
) × R
× 3
LED
L
CS
× 4
R
=
SC
× 50μA × f
MIN
SW
For SEPIC and coupled-inductor configurations (Equation 20):
(V
− V
) × R
× 3
LED
L
IN_MIN
CS
× 4
R
=
SC
× 50μA × f
SW
MIN
where:
● V
● R
and V
are in volts,
IN_MIN
LED
and R
are in ohms,
SC
CS
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Maxim Integrated | 41
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
● L
is in henries, and
MIN
● f
is in hertz.
SW
The value of the switch current-sense resistor (R ) can be calculated using the boost configuration shown in Equation
CS
21.
Equation 21:
4 × L
× f
× 0.39 × 0.9
MIN SW
R
=
CS
I
× 4 × L
× f
+ D
× V
− 2 × V
× 3
(
)
LP
MIN SW
MAX
LED IN_MIN
For SEPIC and coupled-inductor configurations, use Equation 22.
Equation 22:
4 × L
× f
× f
× 0.39 × 0.9
MIN SW
R
=
CS
I
× 4 × L
+ D
× V
− V
× 3
(
)
LP
MIN SW
MAX
LED IN_MIN
where 0.39 is the minimum value of the peak current-sense threshold. The current-sense threshold also includes the
slope-compensation component. The minimum current-sense threshold of 0.39 is multiplied by 0.9 to take tolerances into
account.
Output Capacitor Selection
For all three converter topologies, the output capacitor supplies the load current when the main switch is on. The function
of the output capacitor is to reduce the converter output ripple to acceptable levels. The entire output-voltage ripple
appears across constant-current sink outputs because the LED-string voltages are stable due to the constant current.
For the MAX20446B, limit peak-to-peak output-voltage ripple to 200mV to get stable output current.
Use the following equation to calculate the minimum capacitor value:
I
× DMAX
LED
C
=
OUT(MIN)
0.2 × f
SW
The ESR, ESL, and bulk capacitance of the output capacitor contribute to the output ripple. In most applications, using
low-ESR ceramic capacitors can dramatically reduce the output ESR and ESL effects. To reduce the ESL and ESR
effects, connect multiple ceramic capacitors in parallel to achieve the required bulk capacitance. To minimize audible
noise during PWM dimming, the amount of ceramic capacitors on the output are usually minimized. In this case, an
additional electrolytic or aluminum organic polymer capacitor provides most of the bulk capacitance.
Rectifier Diode Selection
Using a Schottky rectifier diode produces less forward drop and puts the least burden on the MOSFET during reverse
recovery. A diode with considerable reverse-recovery time increases the MOSFET switching loss. Select a Schottky
diode with a voltage rating 20% higher than the maximum boost-converter output voltage and current rating greater than
I
.
LED
Feedback Compensation
During normal operation, the feedback control loop regulates the minimum OUT_ voltage to fall within the window
comparator limits of 0.6V and 0.85V when LED string currents are enabled during PWM dimming. When LED currents
are off during PWM dimming, the control loop turns off the converter and stores the steady-state condition in the form of
capacitor voltages, mainly the output-filter-capacitor voltage and the compensation-capacitor voltage.
The switching converter small-signal-transfer function has a right-half plane (RHP) zero in the boost configuration if the
inductor current is in continuous-conduction mode. The RHP zero adds a 20dB/decade gain together with a 90-degree
phase lag, which is difficult to compensate.
The worst-case RHP zero frequency (f
) is calculated for boost configuration as shown in Equation 23.
ZRHP
Equation 23:
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Maxim Integrated | 42
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
2
V
× 1 − D
(
)
LED
MAX
LED
f
=
ZRHP
2 × π × L × I
For the SEPIC and coupled-inductor configurations, see Equation 24.
Equation 24:
2
V
× 1 − D
(
)
LED
MAX
f
=
ZRHP
2 × π × L × I
× D
LED
MAX
The standard way to avoid this zero is to roll off the loop gain to 0dB at a frequency less than 1/5 of the RHP zero
frequency with a -20dB/decade slope.
The switching converter small-signal transfer function also has an output pole. The effective output impedance, together
with the output filter capacitance, determines the output pole frequency (f ) that is calculated for the boost configuration,
P1
as shown in Equation 25.
Equation 25:
I
LED
f
=
=
P1
π × V
× C
LED
OUT
OUT
For SEPIC and coupled-inductor use Equation 26.
Equation 26:
I
× D
LED
MAX
f
P1
π × V
× C
LED
Compensation components, R
and C
, perform two functions. C
introduces a low-frequency pole that
COMP
COMP
COMP
presents a -20dB/decade slope to the loop gain. R
flattens the gain of the error amplifier for frequencies above the
COMP
zero formed by R
and C
. For compensation, this zero is placed at f to provide a -20dB/decade slope for
COMP P1
COMP
frequencies above f to the combined modulator and compensator response.
P1
The value of R
, needed to fix the total loop gain at f so that the total loop gain crosses 0dB with -20dB/decade
P1
COMP
slope at 1/5 the RHP zero frequency, is calculated as shown in Equation 27.
Equation 27 (for boost configuration):
f
× R
× I
× A
ZRHP
5 × f × GM
CS LED
OVP
R
=
COMP
× V
× 1 − D
(
)
)
P1
COMP
LED
MAX
Equation 28 (for SEPIC and coupled-inductor buck-boost configurations):
f
× R
× I
× A
× D
OVP MAX
ZRHP
CS LED
R
=
COMP
5 × f × GM
× V
× 1 − D
(
P1 LED
COMP
MAX
where:
● R
● A
● R
= Compensation resistor in ohms,
= BSTMON resistor-divider gain (a value << 1),
= Current-sense resistor in ohms, and
COMP
OVP
CS
● GM
= Transconductance of the error amplifier (700μS).
COMP
The value of C
is calculated as shown in Equation 29.
COMP
Equation 29:
1
C
=
COMP
2 × π × f × R
Z1 COMP
where f is the compensation zero placed at 1/5 the crossover frequency, which is, in turn, set at 1/5 the f
. If
ZRHP
Z1
the output capacitors do not have low ESR, the ESR zero frequency could fall below the 0dB crossover frequency. An
additional pole may be required to cancel out this pole placed at the same frequency. This can be added by connecting
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Maxim Integrated | 43
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
a capacitor from the COMP pin directly to GND with a value shown in Equation 30.
Equation 30:
GM
× R
× C
ESR OUT
COMP
where R
is the capacitor ESR value and C
is the output-capacitor value.
OUT
ESR
External Disconnect-MOSFET Selection
An external pMOSFET can be used to disconnect the boost output from the battery in the event of an output overload
or short condition. In the case of the SEPIC or buck-boost, this protection is not necessary so there is no need for
the pMOSFET. Connect the PGATE pin to ground in the case of the SEPIC and buck-boost. If it is necessary to have
an output short protection for the boost even at power-up, then the current through the pMOSFET (see the Typical
Application Circuits) has to be sensed. Once the current-sense voltage exceeds a certain threshold, it should limit the
input current to the programmed threshold. This threshold should be set at a sufficiently high level so it never trips at
startup or under normal operating conditions. Check the safe operating area (SOA) of the pMOSFET so the current-limit
trip threshold and voltage on the MOSFET do not exceed the limits of the SOA curve of the pMOSFET at the highest
operating temperature.
V
to OUT_ Bleed Resistors
OUT
The OUT_ pins have a leakage specification of 12μA (max) in cases where all OUT_ pins are shorted to 48V (see
in Electrical Characteristics). This leakage current is dependent on the OUT_ voltage and is higher at higher
I
OUTLEAK
voltages. Therefore, in cases where large numbers of LEDs are connected in series, a 100kΩ (or larger) bleed resistor
can be placed in parallel with the LED string to prevent the OUT_ leakage current from very dimly illuminating the LEDs,
even when the DIM signal is low (see resistors R8–R11 in Typical Application Circuits).
Thermal Considerations
The on-chip power dissipation of the MAX20446B comprises two main factors:
● Current-sink power loss: 1.1V × I
LED
● Device operating current power loss: V × 15mA.
IN
Calculate the total power dissipation by adding the two values calculated above. The junction temperature at the
maximum ambient temperature can then be calculated using Equation 31.
Equation 31:
T = T + P
× θ
JA
J
A
TOT
where T is the ambient temperature and θ is the junction-to-ambient thermal resistance of the package (36°C/W on a
A
JA
four-layer board). Ensure that the junction temperature does not exceed 150°C.
The general formula for total power dissipation is shown in Equation 32.
Equation 32:
P
= V
× I
+ V × I
LED IN Q
TOT
OUT(MAX)
As an example, consider an application with an operating voltage of 14V and a total output current of 600mA. The total
power dissipation is shown in Equation 33.
Equation 33:
P
= 1.1 × 0.6 + 14 × 0.015 = 0.87W
TOT
The maximum junction temperature at an ambient temperature of 85°C is shown in Equation 34.
Equation 34:
T = 85 + 0.87 × 36 = 116 ° C
J
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Maxim Integrated | 44
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
PCB Layout Considerations
LED driver circuits based on the MAX20446B use a high-frequency switching converter to generate the voltage for LED
strings. Take proper care while laying out the circuit to ensure correct operation. The switching-converter portion of the
circuit has nodes with very fast voltage changes that could lead to undesirable effects on the sensitive parts of the circuit.
Follow the guidelines below to reduce noise as much as possible:
● Connect the bypass capacitor on V
as close as possible to the device and connect the capacitor ground to the
CC
analog ground plane using vias close to the capacitor terminal. Connect the GND of the device to the analog ground
plane using a via close to GND. Lay the analog ground plane on the inner layer, preferably next to the top layer. Use
the analog ground plane to cover the entire area under critical signal components for the power converter.
● Have a power-ground plane for the switching-converter power circuit under the power components (i.e., input filter
capacitor, output filter capacitor, inductor, MOSFET, rectifier diode, and current-sense resistor). Connect PGND to the
power-ground plane closest to PGND. Connect all other ground connections to the power ground plane using vias
close to the terminals.
● There are two loops in the power circuit that carry high-frequency switching currents. One loop is when the MOSFET
is on (from the input filter capacitor positive terminal, through the inductor, the internal MOSFET and the current-
sense resistor, to the input capacitor negative terminal). The other loop is when the MOSFET is off (from the input
capacitor positive terminal, through the inductor, the rectifier diode, output filter capacitor, to the input capacitor
negative terminal). Analyze these two loops and make the loop areas as small as possible. Wherever possible, have
a return path on the power ground plane for the switching currents on the top layer copper traces, or through power
components. This reduces the loop area considerably and provides a low-inductance path for the switching currents.
Reducing the loop area also reduces radiation during switching.
● Connect the power-ground plane for the constant-current LED driver portion of the circuit to LEDGND as close as
possible to the device. Connect GND to PGND at the same point.
● Add a small bypass capacitor (22pF to 47pF) to the BSTMON input. Place the capacitor as close as possible to the
pin to suppress high-frequency noise.
● Boost output voltage for the LED strings should be taken directly from the output capacitors and not from the boost
diode anode.
● Input and output capacitors need good grounding with wide traces and multiple vias to the ground plane.
● Refer to the MAX20446B evaluation kit (EV kit) data sheet for an example layout.
www.maximintegrated.com
Maxim Integrated | 45
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Typical Application Circuits
MAX20446B Applications Circuit
L1
INPUT
VOLTAGE
CIN
10
COUT
NDRV
PGATE
R6
IN
VUC
EN
CS
R5
RSC
FLTB
SDA
SCL
DIM
RCS
R7
FORCE ENABLE
FSEN
MAX20446B
BSTMON
VCC
C1
OUT1
OUT2
OUT3
OUT4
OUT5
OUT6
COMP
RT
RCOMP
IREF
100pF
RT
GND
PGND
LEDGND
49.9kW
CCOMP
Ordering Information
PART
TEMP RANGE
-40 to +125°C
-40 to +125°C
-40 to +125°C
-40 to +125°C
PIN-PACKAGE
24 TQFN
FEATURES
2
MAX20446BATG/V+
MAX20446BATGA/V+*
MAX20446BATG/VY+
MAX20446BATGA/VY+*
Base I C addresses
2
24 TQFN
Alternative I C addresses
2
24 SWTQFN
24 SWTQFN
Base I C addresses
2
Alternative I C addresses
/V denotes an automotive-qualified part.
+Denotes a lead(Pb)-free/RoHS-compliant package.
SW = Side-wettable package
T Denotes Tape and reel.
*Future product - contact factory for availability.
www.maximintegrated.com
Maxim Integrated | 46
MAX20446B
Automotive 6-Channel Backlight Driver with Boost/
2
SEPIC Controller, Hybrid Dimming and I C
Interface
Revision History
REVISION REVISION
PAGES
DESCRIPTION
CHANGED
NUMBER
DATE
12/20
1/21
0
1
Initial release
Added side-wettable package options and package information.
—
3, 42
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max
limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
© 2021 Maxim Integrated Products, Inc.
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