MAX16814AUP/V+T [MAXIM]
LED Driver,;
| 型号： | MAX16814AUP/V+T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | LED Driver, 驱动 接口集成电路 |
| 文件： | 总25页 (文件大小：1076K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
EVALUATION KIT AVAILABLE
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
General Description
Benefits and Features
The MAX16814 high-efficiency, high-brightness LED (HB
LED) driver provides up to four integrated LED current-
sink channels. An integrated current-mode switching
DC-DC controller drives a DC-DC converter that provides
the necessary voltage to multiple strings of HB LEDs.
The MAX16814 accepts a wide 4.75V to 40V input volt-
age range and withstands direct automotive load-dump
events. The wide input range allows powering HB LEDs
for small to medium-sized LCD displays in automotive
and general lighting applications.
● Cost-Effective 4-Channel Linear LED Current Sinks
for Wide Range of LED Lighting Applications
• Drives One to Four LED Strings
• 4.75V to 40V Input Voltage Range
• Full-Scale LED Current Adjustable from 20mA
to 150mA
• 5000:1 PWM Dimming at 200Hz
• Less than 40µA Shutdown Current
● Minimal Component Count Saves Cost and Space
• Internal MOSFET for Each Channel
An internal current-mode switching DC-DC control-
ler supports the boost, coupled-inductor boost-buck,
or SEPIC topologies and operates in an adjustable
frequency range between 200kHz and 2MHz. It can
also be used for single-inductor boost-buck topology in
conjunction with the MAX15054 and an additional
MOSFET. The current-mode control with programma-
ble slope compensation provides fast response and
simplifies loop compensation. The MAX16814 also
features an adaptive output-voltage-control scheme that
minimizes the power dissipation in the LED current-sink
paths.
• Internal Current-Mode Switching DC-DC Controller
Supporting Boost, Coupled-Inductor Boost-Buck, or
SEPIC Topologies
• 200kHz to 2MHz Programmable Switching
Frequency for Optimizing Size vs. Efficiency
• External Switching-Frequency Synchronization
● Protection Features and Wide Operating
Temperature Range improves Reliability
• Open-Drain Fault-Indicator Output
• Open-LED and LED-Short Detection and Protection
• Overtemperature Protection
• Available in Thermally Enhanced 20-Pin TQFN,
QFND, and TSSOP Packages
The MAX16814 consists of four identical linear current
source channels to drive four strings of HB LEDs. The
channel current is adjustable from 20mA to 150mA with
an accuracy of ±±3 using an eꢀternal resistor. The
eꢀternal resistor sets all 4-channel currents to the same
value. The device allows connecting multiple channels
in parallel to achieve higher current per LED string. The
MAX16814 also features pulsed dimming control on all
four channels through a logic input (DIM). In addition,
the MAX16814A_ _ and MAX16814U_ _ include a unique
feature that allows a very short minimum pulse width as
low as 1µs.
• Operation Over -40°C to +125°C Temperature Range
Applications
● Automotive Displays LED Backlights
● Automotive RCL, DRL, Front Position, and Fog Lights
● LCD TV and Desktop Display LED Backlights
● Architectural, Industrial, and Ambient Lighting
The MAX16814 includes output overvoltage, open-
LED detection and protection, programmable shorted-
LED detection and protection, and overtemperature
protection. The device operates over the -40NC to
+125NC automotive temperature range. The MAX16814 is
available in 6.5mm ꢀ 4.4mm, 20-pin TSSOP, 4mm ꢀ 4mm,
20-pin TQFN and QFND packages.
Typical Operating Circuit and Ordering Information appear
at end of data sheet.
19-4722; Rev 11; 3/16
MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Absolute Maximum Ratings
IN to SGND............................................................-0.±V to +45V
Continuous Power Dissipation (T = +70NC) (Note 1)
A
20-Pin TQFN (derate 25.6mW/NC above +70NC).......2051mW
20-Pin Side-Wettable QFND
(derate 26.5mW/NC above +70NC)............................2050mW
26-Pin TSSOP (derate 26.5mW/NC above +70NC).....2122mW
Operating Temperature Range
EN to SGND ...............................................-0.±V to (V + 0.±V)
IN
PGND to SGND....................................................-0.±V to +0.±V
LEDGND to SGND ...............................................-0.±V to +0.±V
OUT_ to LEDGND .................................................-0.±V to +45V
V
CC
to SGND ..........-0.±V to the lower of (V + 0.±V) and +6V
IN
MAX16814A_ _.............................................. -40NC to +125NC
MAX16814BE_ _ ............................................. -40NC to +85NC
MAX16814U_ _and MAX16814BU_ _................0NC to +85NC
Junction Temperature .....................................................+150NC
Storage Temperature Range............................ -65NC to +150NC
Lead Temperature (soldering, 10s) ................................+±00NC
Soldering Temperature (reflow) ......................................+260NC
DRV, FLT, DIM, RSDT, OVP to SGND.....................-0.±V to +6V
CS, RT, COMP, SETI to SGND................. -0.±V to (V
+ 0.±V)
+ 0.±V)
CC
NDRV to PGND .......................................-0.±V to (V
DRV
NDRV Peak Current (< 100ns)............................................. Q±A
NDRV Continuous Current ............................................ Q100mA
OUT_ Continuous Current............................................. Q175mA
V
Short-Circuit Duration........................................Continuous
CC
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional opera-
tion 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 Thermal Characteristics (Note 1)
20 TQFN/QFND
Junction-to-Ambient Thermal Resistance (B )........ +±9NC/W
20 TSSOP
Junction-to-Ambient Thermal Resistance (B )..... +±7.7NC/W
JA
JA
Junction-to-Case Thermal Resistance (B )............... +6NC/W
Junction-to-Case Thermal Resistance (B )............ +2.0NC/W
JC
JC
Note 1: 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 http://www.maximintegrated.com/thermal-tutorial.
Electrical Characteristics
(V = V = 12V, R = 12.25kI, R
= 15kI, C
= 1FF, V
= V , NDRV = COMP = OUT_ = unconnected, V = V
DRV RSDT DIM
IN
EN
RT
SETI
VCC
CC
= V , V
= V
= V
= V
= V = 0V, T = T = -40NC to +125NC for MAX16814A_ _, T = -40NC to +85NC for
SGND A J A
CC OVP
CS
LEDGND
PGND
MAX16814BE_ _, and T = T = 0NC to +85NC for MAX16814U_ _ and MAX16814BU_ _, unless otherwise noted. Typical values are at
A
J
T
A
= +25NC.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
40
UNITS
Operating Voltage Range
V
4.75
V
IN
MAX16814A_ _ and MAX16814U_ _
MAX16814B_ _ _ only
2.5
2.75
15
5
Active Supply Current
I
mA
IN
5.5
40
Standby Supply Current
IN Undervoltage Lockout
IN UVLO Hysteresis
V
EN
V
IN
= 0V
µA
V
rising
±.975
4.75
4.±
4.625
170
mV
V
CC
REGULATOR
6.5V < V < 10V, 1mA < I
< 50mA
< 10mA
IN
LOAD
Regulator Output Voltage
V
CC
5.0
5.25
500
V
10V < V < 40V, 1mA < I
IN
LOAD
Dropout Voltage
V
V
- V , V = 4.75V, I = 50mA
LOAD
200
100
mV
mA
IN
CC IN
Short-Circuit Current Limit
shorted to SGND
CC
V
Undervoltage Lockout
CC
V
CC
rising
4
V
Threshold
V
CC
UVLO Hysteresis
100
mV
RT OSCILLATOR
Switching Frequency Range
f
200
2000
kHz
SW
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Electrical Characteristics (continued)
(V = V = 12V, R = 12.25kI, R
= 15kI, C
= 1FF, V
= V , NDRV = COMP = OUT_ = unconnected, V = V
DRV RSDT DIM
IN
EN
RT
SETI
VCC
CC
= V , V
= V
= V
= V
= V = 0V, T = T = -40NC to +125NC for MAX16814A_ _, T = -40NC to +85NC for
SGND A J A
CC OVP
CS
LEDGND
PGND
MAX16814BE_ _, and T = T = 0NC to +85NC for MAX16814U_ _ and MAX16814BU_ _, unless otherwise noted. Typical values are at
A
J
T
A
= +25NC.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
f
= 200kHz to 600kHz, MAX16814A_ _
SW
85
89
9±
and MAX16814U_ _
f
= 600kHz to 2000kHz, MAX16814A_ _
SW
82
86
90
Maꢀimum Duty Cycle
3
and MAX16814U_ _
f
f
f
= 200kHz to 600kHz, MAX16814B_ _
= 600kHz to 2000kHz, MAX16814B _ _ _
= 200kHz to 2MHz, MAX16814A_ _
90
86
94
90
98
94
SW
SW
SW
-7.5
+7.5
+7
and MAX16814U_ _
Oscillator Frequency Accuracy
3
f
= 200kHz to 2MHz, MAX16814B_ _ _
-7
4
SW
Sync Rising Threshold
V
Minimum Sync Frequency
1.1f
Hz
SW
PWM COMPARATOR
PWM Comparator Leading-Edge
Blanking Time
PWM to NDRV Propagation Delay
60
90
ns
ns
Including leading-edge blanking time
SLOPE COMPENSATION
Current ramp added to the CS input,
MAX16814A_ _ only
Current ramp added to the CS input,
MAX16814U_ _ and MAX16814B_ _ _
44
45
49
50
54
55
Peak Slope Compensation
Current Ramp Magnitude
µA ꢀ f
SW
CS LIMIT COMPARATOR
Current-Limit Threshold
CS Limit Comparator to NDRV
Propagation Delay
(Note ±)
±96
416
10
4±7
mV
ns
10mV overdrive, eꢀcluding leading-edge
blanking time
ERROR AMPLIFIER
OUT_ Regulation Voltage
Transconductance
No-Load Gain
1
V
g
±40
600
75
880
µS
dB
µA
µA
M
(Note 4)
COMP Sink Current
COMP Source Current
MOSFET DRIVER
V
OUT_
OUT_
= 5V, V
= 2.5V
= 2.5V
160
160
±75
±75
800
800
COMP
COMP
V
= 0V, V
I
I
= 100mA (nMOS)
0.9
1.1
2.0
2.0
6
SINK
NDRV On-Resistance
ω
= 100mA (pMOS)
SOURCE
Peak Sink Current
Peak Source Current
Rise Time
V
V
= 5V
A
A
NDRV
NDRV
= 0V
C
= 1nF
= 1nF
ns
ns
LOAD
LOAD
Fall Time
C
6
LED CURRENT SOURCES
OUT_ Current-Sink Range
V
= V
20
150
±2
mA
3
OUT_
REF
I
I
= 100mA
OUT_
OUT_
Channel-to-Channel Matching
= 100mA, all channels on
±1.5
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Electrical Characteristics (continued)
(V = V = 12V, R = 12.25kI, R
= 15kI, C
= 1FF, V
= V , NDRV = COMP = OUT_ = unconnected, V = V
DRV RSDT DIM
IN
EN
RT
SETI
VCC
CC
= V , V
= V
= V
= V
= V = 0V, T = T = -40NC to +125NC for MAX16814A_ _, T = -40NC to +85NC for
SGND A J A
CC OVP
CS
LEDGND
PGND
MAX16814BE_ _, and T = T = 0NC to +85NC for MAX16814U_ _ and MAX16814BU_ _, unless otherwise noted. Typical values are at
A
J
T
A
= +25NC.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
T
only
= +125°C, MAX16814A_ _
A
±±
I
=
OUT_
100mA
T
= -40°C to +125°C,
A
±5
±2.75
±4
MAX16814A_ _ only
T
= +25°C, MAX16814U_ _ and
A
Output Current Accuracy
3
MAX16814B_ _ _
I
=
OUT_
T
= 0°C to +85°C, MAX16814U_
A
50mA to
150mA
_ and MAX16814BU _ _
T
= -40°C to +85°C for
A
±4
MAX16814BE _ _
OUT_ Leakage Current
V
= 0V, V = 40V
1
µA
V
DIM
OUT_
LOGIC INPUTS/OUTPUTS
V
V
rising, MAX16814A_ _ only
rising, MAX16814U_ _ and
1.125
1.144
1.2±
1.2±
50
1.±±5
1.±16
EN
EN
EN Reference Voltage
MAX16814B_ _ _
EN Hysteresis
mV
nA
V
EN Input Current
V
= 40V
±600
0.8
EN
DIM Input High Voltage
DIM Input Low Voltage
DIM Hysteresis
2.1
V
250
mV
µA
ns
ns
ns
V
DIM Input Current
±2
DIM to LED Turn-On Delay
DIM to LED Turn-Off Delay
DIM rising edge to 103 rise in I
DIM falling edge to 103 fall in I
100
100
200
OUT_
OUT_
I
Rise and Fall Times
OUT_
FLT Output Low Voltage
V
V
= 4.75V and I
= 5mA
0.4
1.0
IN
SINK
FLT Output Leakage Current
LED Short Detection Threshold
Short Detection Comparator Delay
RSDT Leakage Current
= 5.5V
µA
V
FLT
Gain = ±V
1.75
1.19
2.0
6.5
2.25
µs
nA
V
±600
1.266
OVP Trip Threshold
Output rising
1.228
70
OVP Hysteresis
mV
nA
°C
°C
OVP Leakage Current
V
= 1.25V
±200
OVP
Thermal-Shutdown Threshold
Thermal-Shutdown Hysteresis
Temperature rising
165
15
Note 2: All MAX16814A_ _ are 1003 tested at T = +125NC, while all MAX16814U_ _ and MAX16814B _ _ _ are 1003 tested at
A
T
= +25°C. All limits overtemperature are guaranteed by design, not production tested.
A
Note 3: CS threshold includes slope-compensation ramp magnitude.
Note 4: Gain = δV /δV , 0.05V < V < 0.15V.
COMP
CS
CS
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Typical Operating Characteristics
(V = V = 12V, f
= ±00kHz, R
= 15kI, C
= 1FF, V
= V
, NDRV = COMP = OUT_ = unconnected, V
DRV
= V
CS
=
IN
EN
SW
SETI
VCC
CC
OVP
V
= V
= V
= V = 0V, load = 4 strings of 7 white LEDs, T = +25NC, unless otherwise noted.)
SGND A
LEDGND
DIM
PGND
SWITCHING WAVEFORM AT 5kHz
(50% DUTY CYCLE) DIMMING
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX16814 toc01
3.8
3.6
3.4
3.2
3.0
2.8
2.6
2.4
C
= 13pF
NDRV
T
A
= +125NC
V
LX
10V/div
0V
T
A
= +25NC
I
OUT1
100mA/div
0A
T
A
= -40NC
V
OUT
10V/div
FIGURE 2
0V
5
10 15 20 25 30 35 40 45
40Fs/div
V
(V)
IN
SUPPLY CURRENT
vs. SWITCHING FREQUENCY
SWITCHING FREQUENCY
vs. TEMPERATURE
V
vs. TEMPERATURE
SETI
1.240
1.236
1.232
1.228
1.224
1.220
4.4
310
C
= 13pF
NDRV
308
306
304
302
300
298
296
294
292
290
4.2
4.0
3.8
3.6
3.4
3.2
3.0
-50 -25
0
25
50
75 100 125
200 400 600 800 1000 1200 1400 1600 1800 2000
(kHz)
-50 -25
0
25
50
75 100 125
TEMPERATURE (NC)
f
TEMPERATURE (NC)
SW
EN THRESHOLD VOLTAGE
vs. TEMPERATURE
EN LEAKAGE CURRENT
vs. TEMPERATURE
V
SETI
vs. PROGRAMMED CURRENT
1.234
1.233
1.232
1.231
1.230
1.229
1.228
150
120
90
60
30
0
1.30
1.25
1.20
1.15
1.10
V
= 2.5V
EN
V
RISING
EN
V
FALLING
EN
20
46
72
98
124
150
-50 -25
0
25
50
75 100 125
-50 -25
0
25
50
75 100 125
LED STRING CURRENT (mA)
TEMPERATURE (NC)
TEMPERATURE (NC)
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Typical Operating Characteristics (continued)
(V = V = 12V, f
= ±00kHz, R
= 15kI, C
= 1FF, V
= V
, NDRV = COMP = OUT_ = unconnected, V
DRV
= V
CS
=
IN
EN
SW
SETI
VCC
CC
OVP
V
= V
= V
= V = 0V, load =4 strings of 7 white LEDs, T = +25NC, unless otherwise noted.)
SGND A
LEDGND
DIM
PGND
SWITCHING FREQUENCY vs. 1/RT
V
CC
LINE REGULATION
V
LOAD REGULATION
CC
5.10
5.08
5.06
5.04
5.02
5.00
4.98
4.96
4.94
4.92
4.90
2.00
1.80
1.60
1.40
1.20
1.00
0.80
0.60
0.40
0.20
5.08
5.06
5.04
5.02
5.00
4.98
T
A
= +125NC
T
= +125NC
A
T
= +25NC
A
T
A
= +25NC
T
= -40NC
A
T
A
= -40NC
4.96
5
0.02 0.06 0.10 0.14 0.18 0.22 0.26 0.30
1/RT (mS)
10
15
20
25
(V)
30
35
40
0
20
40
60
80
V
I
(mA)
VCC
IN
STARTUP WAVEFORM WITH
STARTUP WAVEFORM WITH DIM
DIM ON PULSE WIDTH < t
ON PULSE WIDTH = 10t
SW
SW
MAX16814 toc12
MAX16814 toc13
V
IN
V
IN
20V/div
0V
20V/div
0V
V
DIM
V
DIM
5V/div
0V
5V/div
0V
I
I
OUT_
OUT1
100mA/div
0A
100mA/div
0A
V
LED
V
LED
10V/div
20V/div
FIGURE 2
0V
0V
40ms/div
40ms/div
MOSFET DRIVER ON-RESISTANCE
vs. TEMPERATURE
STARTUP WAVEFORM WITH DIM
CONTINUOUSLY ON
MAX16814 toc14
1.5
1.3
1.1
0.9
0.7
0.5
V
IN
20V/div
0V
V
DIM
pMOS
5V/div
0V
I
OUT1
100mA/div
0A
nMOS
V
LED
10V/div
FIGURE 2
0V
-50 -25
0
25
50
75 100 125
40ms/div
TEMPERATURE (NC)
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Typical Operating Characteristics (continued)
(V = V = 12V, f
= ±00kHz, R
= 15kI, C
= 1FF, V
= V
, NDRV = COMP = OUT_ = unconnected, V
DRV
= V
CS
=
IN
EN
SW
SETI
VCC
CC
OVP
V
= V
= V
= V = 0V, load = 4 strings of 7 white LEDs, T = +25NC, unless otherwise noted.)
SGND A
LEDGND
DIM
PGND
LED CURRENT RISING AND FALLING
LED CURRENT SWITCHING WITH DIM
WAVEFORM
AT 5kHz AND 50% DUTY CYCLE
MAX16814 toc17
MAX16814 toc16
FIGURE 2
I
V
OUT1
DIM
100mA/div
0A
5V/div
0V
I
OUT2
100mA/div
0A
I
I
LED
OUT3
50mA/div
0A
100mA/div
0A
I
OUT4
FIGURE 2
100mA/div
0A
4Fs/div
100Fs/div
COMP LEAKAGE CURRENT
vs. TEMPERATURE
OUT_ CURRENT vs. 1/R
SETI
160
140
120
100
80
1.0
0.8
0.6
0.4
0.2
0
V
= 0V
DIM
V
= 4.5V
COMP
V
= 0.5V
COMP
60
40
20
0.010 0.025 0.040 0.055 0.070 0.085 0.100
-50 -25
0
25
50
75 100 125
1/R (mS)
SETI
TEMPERATURE (NC)
OUT_ LEAKAGE CURRENT
vs. TEMPERATURE
OVP LEAKAGE CURRENT
vs. TEMPERATURE
RSDT LEAKAGE CURRENT
vs. TEMPERATURE
100
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
250
200
150
100
50
V
V
= 0V
= 40V
DIM
OUT
V
= 1.25V
OVP
10
1
V
V
= 0.5V
RSDT
RSDT
= 2.5V
50
0.1
-50 -25
0
25
50
75 100 125
-50 -25
0
25
50
75 100 125
-50 -25
0
25
75 100 125
TEMPERATURE (NC)
TEMPERATURE (NC)
TEMPERATURE (NC)
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Pin Configurations
TOP VIEW
TOP VIEW
+
15
14
13
12
11
NDRV
DRV
1
2
3
4
5
6
7
8
9
20 PGND
19 CS
DIM
10
9
CS 16
PGND 17
NDRV 18
DRV 19
V
18 OUT4
17 OUT3
16 LEDGND
15 OUT2
14 OUT1
13 DIM
CC
IN
SGND
MAX16814
MAX16814
8
RSDT
SETI
OVP
EN
COMP
RT
7
EP*
20
6
V
CC
FLT
1
2
3
4
5
OVP
12 SGND
11 RSDT
EP*
SETI 10
TQFN/QFND
TSSOP
*EXPOSED PAD.
Pin Description
PIN
NAME
FUNCTION
TQFN/
TSSOP
QFND
Bias Supply Input. Connect a 4.75V to 40V supply to IN. Bypass IN to SGND with a ceramic
capacitor.
1
2
±
4
5
6
IN
EN
Enable Input. Connect EN to logic-low to shut down the device. Connect EN to logic-high or IN
for normal operation. The EN logic threshold is internally set to 1.2±V.
Switching Converter Compensation Input. Connect the compensation network from COMP to
SGND for current-mode control (see the Feedback Compensation section).
COMP
Oscillator Timing Resistor Connection. Connect a timing resistor (R ) from RT to SGND to program
T
9
the switching frequency according to the formula R = 7.±50 ꢀ 10 /f (for the MAX16814A_ _
T
sw
4
7
RT
9
and the MAX16814U_ _) or to the formula R = 7.72 ꢀ 10 /f (for the
an
MAX16814B_ _ _). Apply
T
sw
AC-coupled eꢀternal clock at RT to synchronize the switching frequency with an eꢀternal clock.
Open-Drain Fault Output. FLT asserts low when an open LED, short LED, or thermal shutdown
5
6
7
8
9
FLT
OVP
SETI
is detected. Connect a 10kω pullup resistor from FLT to V
.
CC
Overvoltage-Threshold-Adjust Input. Connect a resistor-divider from the switching converter
output to OVP and SGND. The OVP comparator reference is internally set to 1.2±V.
LED Current-Adjust Input. Connect a resistor (R ) from SETI to SGND to set the current
SETI
10
through each LED string (I
) according to the formula I
= 1500/R
.
LED
LED
SETI
LED Short Detection Threshold Adjust Input. Connect a resistive divider from V
to RSDT and
CC
8
9
11
12
RSDT
SGND to program the LED short detection threshold. Connect RSDT directly to V
LED short detection. The LED short detection comparator is internally referenced to 2V.
to disable
CC
Signal Ground. SGND is the current return path connection for the low-noise analog signals.
Connect SGND, LEDGND, and PGND at a single point.
SGND
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Pin Description (continued)
PIN
NAME
DIM
FUNCTION
TQFN/
QFND
TSSOP
Digital PWM Dimming Input. Apply a PWM signal to DIM for LED dimming control. Connect DIM
10
1±
to V
if dimming control is not used.
CC
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 150mA. If
unused, connect OUT1 to LEDGND.
11
14
OUT1
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 150mA. If
unused, connect OUT2 to LEDGND.
12
1±
14
15
16
17
OUT2
LEDGND
OUT±
LED Ground. LEDGND is the return path connection for the linear current sinks. Connect
SGND, LEDGND, and PGND at a single point.
LED String Cathode Connection ±. OUT± is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT±. OUT± sinks up to 150mA. If
unused, connect OUT± to LEDGND.
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 150mA. If
unused, connect OUT4 to LEDGND.
15
16
18
19
OUT4
CS
Current-Sense Input. CS is the current-sense input for the switching regulator. A sense resistor
connected from the source of the eꢀternal 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 section).
Power Ground. PGND is the switching current return path connection. Connect SGND,
LEDGND, and PGND at a single point.
17
18
20
1
PGND
NDRV
Switching n-MOSFET Gate-Driver Output. Connect NDRV to the gate of the eꢀternal switching
power MOSFET.
MOSFET Gate-Driver Supply Input. Connect a resistor between V
and DRV to power the
CC
19
2
DRV
MOSFET driver with the internal 5V regulator. Bypass DRV to PGND with a minimum of 0.1µF
ceramic capacitor.
5V Regulator Output. Bypass V
as possible to the device.
to SGND with a minimum of 1µF ceramic capacitor as close
CC
20
—
±
V
CC
Eꢀposed 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 SGND.
—
EP
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
FLT
RSDT
V
REF
POKD
MAX16814
UNUSED
STRING
DETECTOR
SHORT LED
DETECTOR
OPEN-LED
DETECTOR
FAULT FLAG
LOGIC
SHDN
DRV
TSHDN
PWM
LOGIC
NDRV
PGND
CLK
MIN STRING
VOLTAGE
SLOPE
COMPENSATION
RAMP/RT OSC
OUT_
ILIM
RT
0.425V
2.5V
di
dt
(
= 50FA x f
)
sw
CS BLANKING
CS
COMP
OVP
COMP
R
LOGIC
SHDN
THERMAL
SHUTDOWN
g
M
TSHDN
REF
FB
V
BG
BANDGAP
IN
LEDGND
DIM
LOGIC
(REF/FB
SELECTOR)
UVLO
V
BG
= 1.235V
5V LDO
REGULATOR
V
CC
SS_DONE
SS_REF
V
REF
UVLO
TSHDN
POK
SOFT-START
100ms
SHDN
POKD
V
BG
P
EN
SHDN
1.23V
TSHDN
SGND
SGND
OVP
SETI
Figure 1. Simplified Functional Diagram
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
V
7 HBLEDS
PER STRING
IN
L2
D1
L1
C2
C1
C7
C5
C6
R1
R2
M1
C8
D2
R7
R
SCOMP
R
CS
IN
NDRV
CS
OVP
EN
OUT1
OUT2
V
CC
C3
OUT3
OUT4
R5
MAX16814
VDRV
C4
R
SETI
SETI
V
CC
DIM
R6
R3
FLT
COMP
RSDT
R4
R
COMP
R
T
R
T
C
COMP
SGND
PGND
LEDGND
Figure 2. Circuit Used for Typical Operating Characteristics
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Detailed Description
protection thresholds are programmable using RSDT
and OVP inputs, respectively. An open-drain FLT signal
asserts to indicate open-LED, shorted-LED, and over-
temperature conditions. Disable individual current-sink
channels by connecting the corresponding OUT_ to
LEDGND. In this case, FLT does not assert indicating
an open-LED condition for the disabled channel. The
device also features an overtemperature protection that
shuts down the controller if the die temperature eꢀceeds
+165NC.
The MAX16814 high-efficiency HB LED driver
integrates all the necessary features to implement a
high-performance backlight driver to power LEDs in
small to medium-sized displays for automotive as well
as general applications. The device provides load-dump
voltage protection up to 40V in automotive applications.
The MAX16814 incorporates two major blocks: a DC-DC
controller with peak current-mode control to implement
a boost, coupled-inductor boost-buck, or a SEPIC-type
switched-mode power supply and a 4-channel LED
driver with 20mA to 150mA constant current-sink capa-
bility per channel. Figure 1 is the simplified functional
diagram and Figure 2 shows the circuit used for typical
operating characteristics.
Current-Mode DC-DC Controller
The peak current-mode controller allows boost, coupled-
inductor buck-boost, or SEPIC-type converters to generate
the required bias voltage for the LED strings. The switch-
ing frequency can be programmed over the 200kHz to
2MHz range using a resistor connected from RT to SGND.
Programmable slope compensation is available to com-
pensate for subharmonic oscillations that occur at above
503 duty cycles in continuous-conduction mode.
The MAX16814 features a constant-frequency peak
current-mode control with programmable slope
compensation to control the duty cycle of the PWM
controller. The high-current FET driver can provide up
to 2A of current to the eꢀternal n-channel MOSFET.
The DC-DC converter implemented using the controller
generates the required supply voltage for the LED
strings from a wide input supply range. Connect LED
strings from the DC-DC converter output to the 4-channel
constant current-sink drivers that control the current
through the LED strings. A single resistor connected
from the SETI input to ground adjusts the forward current
through all four LED strings.
The eꢀternal 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
)
CS
connected from the source of the eꢀternal MOSFET to
PGND. The MAX16814 features leading-edge blanking to
suppress the eꢀternal MOSFET switching noise. A PWM
comparator compares the current-sense voltage plus the
slope-compensation signal with the output of the trans-
conductance error amplifier. The controller turns off the
eꢀternal MOSFET when the voltage at CS eꢀceeds the
error amplifier’s output voltage. This process repeats every
switching cycle to achieve peak current-mode control.
The MAX16814 features adaptive voltage control that
adjusts the converter output voltage depending on the
forward voltage of the LED strings. This feature mini-
mizes the voltage drop across the constant current-sink
drivers and reduces power dissipation in the device. A
logic input (EN) shuts down the device when pulled low.
The device includes an internal 5V LDO capable of pow-
ering additional eꢀternal circuitry.
Error Amplifier
The internal error amplifier compares an internal feed-
back (FB) with an internal reference (REF) and regulates
its output to adjust the inductor current. An internal mini-
mum string detector measures the minimum current-sink
voltage with respect to SGND out of the four constant-
current-sink channels. During normal operation, this
minimum OUT_ voltage is regulated to 1V through
feedback. The error amplifier takes 1V as the REF
and the minimum OUT_ voltage as the FB input. The
amplified error at the COMP output controls the inductor
peak current to regulate the minimum OUT_ voltage at
1V. The resulting DC-DC converter output voltage is the
highest LED string voltage plus 1V.
All the versions of the MAX16814 include PWM dimming.
The MAX16814A_ and the MAX16814U_ versions, in par-
ticular, provide very wide (5000:1) PWM dimming range
where a dimming pulse as narrow as 1µs is possible at
a 200Hz dimming frequency. This is made possible by
a unique feature that detects short PWM dimming input
pulses and adjusts the converter feedback accordingly.
Advanced features include detection and string-
disconnect for open-LED strings, partial or fully shorted
strings, and unused strings. Overvoltage protection
clamps the converter output voltage to the programmed
OVP threshold in the event of an open-LED condi-
tion. Shorted LED string detection and overvoltage
The converter stops switching when the LED strings are
turned off during PWM dimming. The error amplifier is
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
disconnected from the COMP output to retain the com-
pensation capacitor charge. This allows the converter
to settle to steady-state level almost immediately when
the LED strings are turned on again. This unique feature
provides fast dimming response, without having to use
large output capacitors.
953 of the OVP voltage and uses feedback from the OVP
input. Soft-start terminates when the minimum current-sink
voltage reaches 1V or when the converter output reaches
953 OVP. The typical soft-start period is 100ms. The 1V
minimum OUT_ voltage is detected only when the LED
strings are enabled by PWM dimming. Connect OVP to
the boost converter output through a resistive divider
network (see the Typical Operating Circuit).
For the MAX16814A_ _ and the MAX16814U_ _, if the
PWM dimming on-pulse is less than or equal to five
switching cycles, the feedback controls the voltage on
OVP so that the converter output voltage is regulated at
953 of the OVP threshold. This mode ensures that narrow
PWM dimming pulses are not affected by the response
time of the converter. During this mode, the error amplifier
remains connected to the COMP output continuously and
the DC-DC converter continues switching.
When there is an open-LED condition, the converter output
hits the OVP threshold. After the OVP is triggered, open-
LED strings are disconnected and, at the beginning of the
dimming PWM pulse, control is transferred to the adaptive
voltage control. The converter output discharges to a level
where the new minimum OUT_ voltage is 1V.
Oscillator Frequency/External Synchronization
Undervoltage Lockout (UVLO)
The internal oscillator frequency is programmable
The MAX16814 features two undervoltage lockouts that
monitor the input voltage at IN and the output of the inter-
between 200kHz and 2MHz using a resistor (R ) con-
nected from the RT input to SGND. Use the equation
T
nal LDO regulator at V . The device turns on after both
below to calculate the value of R for the desired switch-
CC
T
V
IN
and V
eꢀceed their respective UVLO thresholds.
ing frequency, f
.
CC
SW
The UVLO threshold at IN is 4.±V when V is rising and
IN
9
7.±5×10 Hz
4.15V when V is falling. The UVLO threshold at V
is
IN
CC
R
=
T
4V when V
is rising and ±.9V when V
is falling.
f
CC
CC
SW
Enable
(for the MAX16814A_ _ and the MAX16814U_ _).
EN is a logic input that completely shuts down the
device when connected to logic-low, reducing the
current consumption of the device to less than 40FA.
The logic threshold at EN is 1.2±V (typ). The voltage
at EN must eꢀceed 1.2±V before any operation can
commence. There is a 50mV hysteresis on EN. The EN
input also allows programming the supply input UVLO
threshold using an eꢀternal voltage-divider to sense the
input voltage as shown below.
9
7.72 ×10
R
=
T
f
SW
(for the MAX16814B_ _ _).
Synchronize the oscillator with an eꢀternal clock by
AC-coupling the eꢀternal clock to the RT input. The
capacitor used for the AC-coupling should satisfy the
following relation:
Use the following equation to calculate the value of R1
and R2 in Figure ±:
9.862
R
T
-±
C
≤
-0.144×10
µF
(
)
SYNC
V
UVLO
R1 =
- 1 ×R2
1.2±V
where R is in Ω.
T
where V
is the desired undervoltage lockout level
UVLO
V
IN
and 1.2±V is the EN input reference. Connect EN to IN
if not used.
MAX16814
R1
R2
EN
Soft-Start
The MAX16814 provides soft-start with internally set timing. At
power-up, the MAX16814 enters soft-start once unused LED
strings are detected and disconnected (see the Open-LED
Management and Overvoltage Protection section). During
soft-start, the DC-DC converter output ramps towards
1.23V
Figure 3. Setting the MAX16814 Undervoltage Lockout
Threshold
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
The pulse width for the synchronization pulse should
satisfy the following relations:
BOOST CONVERTER
OUTPUT
t
PW
V < 0.5
S
t
CLK
40mA TO 300mA
PER STRING
t
PW
0.8 −
V
+ V > ±.4
S
S
t
CLK
t
CLK
t
<
t
− 1.05×t
CLK
(
)
OUT1
PW
CI
t
CI
MAX16814
OUT2
OUT3
OUT4
where t
is the synchronization source pulse width,
is the synchronization clock time period, t
programmed clock period, and
pulse voltage level.
PW
t
CLK
CI is the
V
is the synchronization
S
5V LDO Regulator (V
)
CC
The internal LDO regulator converts the input voltage
Figure 4. Configuration for Higher LED String Current
at IN to a 5V output voltage at V . The LDO regulator
CC
supplies up to 50mA current to provide power to internal
control circuitry and the gate driver. Connect a resistor
where I
four channels.
is the desired output current for each of the
OUT_
between V
and DRV to power the gate-drive circuitry;
CC
If more than 150mA is required in an LED string, use two
or more of the current source outputs (OUT_) connected
together to drive the string as shown in Figure 4.
the recommended value is 4.7I. Bypass DRV with a
capacitor to PGND. The eꢀternal resistor and bypass
capacitor provide noise filtering. Bypass V
to SGND
CC
with a minimum of 1FF ceramic capacitor as close to the
device as possible.
LED Dimming Control
The MAX16814 features LED brightness control using an
eꢀternal PWM signal applied at DIM. A logic-high signal
on the DIM input enables all four LED current sources
and a logic-low signal disables them.
PWM MOSFET Driver
The NDRV output is a push-pull output with the on-resis-
tance of the pMOS typically 1.1I and the on-resistance
of the nMOS typically 0.9I. NDRV swings from PGND to
DRV to drive an eꢀternal n-channel MOSFET. The driver
typically sources 2.0A and sinks 2.0A allowing for fast
turn-on and turn-off of high gate-charge MOSFETs.
For the MAX16814A_ _ and the MAX16814U_ _, the duty
cycle of the PWM signal applied to DIM also controls
the DC-DC converter’s output voltage. If the turn-on
duration of the PWM signal is less than or equal to 5
oscillator clock cycles (DIM pulse width decreasing) then
the boost converter regulates its output based on feed-
back from the OVP input. During this mode, the converter
output voltage is regulated to 953 of the OVP threshold
voltage. If the turn-on duration of the PWM signal is
greater than or equal to 6 oscillator clock cycles (DIM
pulse width increasing), then the converter regulates its
output so that the minimum voltage at OUT_ is 1V.
The power dissipation in the MAX16814 is mainly a
function of the average current sourced to drive the
eꢀternal MOSFET (I ) if there are no additional loads
DRV
on V . I
depends on the total gate charge (Q )
CC DRV
G
and operating frequency of the converter. Connect DRV
to V with a 4.7I resistor to power the gate driver with
CC
the internal 5V regulator.
LED Current Control
When the DIM signal crosses the 5 or 6 oscillator clock-
cycle boundary, the control loop of the MAX16814
eꢀperiences a discontinuity due to an internal mode
transition, which can cause flickering (the boost output
voltage changes, as described in previous paragraph).
To avoid flicker, the following is recommended:
The MAX16814 features four identical constant-current
sources used to drive multiple HB LED strings. The
current through each one of the four channels is adjust-
able between 20mA and 150mA using an eꢀternal
resistor (R
) connected between SETI and SGND.
SETI
Select R
using the following formula:
SETI
● Avoid crossing the 5 or 6 oscillator clock-cycle
R
= 1500 I
OUT_
boundary.
SETI
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
● Do not set the OVP level higher than ±V
converter
protection threshold, the PWM controller is switched off,
setting NDRV low. Any current-sink output with V
< ±00mV (typ) is disconnected from the minimum voltage
detector.
output
reaches
the
overvoltage
above the maꢀimum LED operating voltage.
OUT_
● Optimize the compensation components so
that recovery is as fast as possible. If the loop
phase margin is less than 45°, the output voltage
may ring during the 5 or 6 oscillator clock-cycle
boundary crossing, which can contribute to flicker.
Connect the OUT_ of all channels without LED
connections to LEDGND before power-up to avoid OVP
triggering at startup. When an open-LED overvoltage
condition occurs, FLT is latched low.
Fault Protections
Fault protections in the MAX16814 include cycle-
by-cycle current limiting using the PWM controller,
DC-DC converter output overvoltage protection, open-
LED detection, short LED detection and protection, and
overtemperature shutdown. An open-drain LED fault
flag output (FLT) goes low when an open-LED string
is detected, a shorted LED string is detected, and
during thermal shutdown. FLT is cleared when the fault
condition is removed during thermal shutdown and
shorted LEDs. FLT is latched low for an open-LED
condition and can be reset by cycling power or toggling
the EN pin. The thermal shutdown threshold is +165NC
and has 15NC hysteresis.
Short-LED Detection
The MAX16814 checks for shorted LEDs at each rising
edge of DIM. An LED short is detected at OUT_ if the fol-
lowing condition is met:
V
OUT_
> V
+ ± ꢀ V
MINSTR RSDT
where V
is the voltage at OUT_, V
is
is the
OUT_
MINSTR
RSDT
the minimum current-sink voltage, and V
programmable LED short detection threshold set at
the RSDT input. Adjust V using a voltage-divider
resistive network connected at the V
input, and SGND.
RSDT
output, RSDT
CC
Once a short is detected on any of the strings, the LED
strings with the short are disconnected and the FLT
output flag asserts until the device detects that the shorts
are removed on any of the following rising edges of DIM.
Connect RSDT directly to V
short detection.
Open-LED Management and
Overvoltage Protection
On power-up, the MAX16814 detects and disconnects
any unused current-sink channels before entering
soft-start. Disable the unused current-sink channels
by connecting the corresponding OUT_ to LEDGND.
This avoids asserting the FLT output for the unused
channels. After soft-start, the MAX16814 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. 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 always disable LED
CC
Applications Information
DC-DC Converter
Three different converter topologies are possible with
the DC-DC controller in the MAX16814, which has
the ground-referenced outputs necessary to use the
constant current-sink drivers. If the LED string forward
voltage is always more than the input supply voltage
range, use the boost converter topology. If the LED string
forward voltage falls within the supply voltage range, use
the boost-buck converter topology. Boost-buck topology
is implemented using either a conventional SEPIC con-
figuration or a coupled-inductor boost-buck configura-
tion. 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. Figure 6 shows
the coupled-inductor boost-buck configuration. It is also
possible to implement a single inductor boost-buck con-
verter using the MAX15054 high-side FET driver.
to V . The DC-DC converter output voltage then
LEDGND
increases to the overvoltage protection threshold set by
the voltage-divider network connected between the con-
verter output, OVP input, SGND. The overvoltage protec-
tion threshold at the DC-DC converter output (V
determined using the following formula:
) is
OVP
R1
R2
(see the Typical Operating Circuit)
V
=1.2± × 1+
OVP
The boost converter topology provides the highest effi-
ciency among the above mentioned topologies. The
coupled-inductor boost-buck topology has the advan-
where 1.2±V (typ) is the OVP threshold. Select R1 and
R2 such that the voltage at OUT_ does not eꢀceed
the absolute maꢀimum rating. As soon as the DC-DC
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
tage of not using a coupling capacitor over the SEPIC
configuration. Also, the feedback loop compensation for
SEPIC becomes compleꢀ if the coupling capacitor is not
large enough. A coupled-inductor boost-buck is not suit-
able for cases where the coupled-inductor windings are
not tightly coupled. Considerable leakage inductance
requires additional snubber components and degrades
the efficiency.
maꢀimum average current occurs at the lowest line
voltage. For the boost converter, the average inductor
current is equal to the input current. Select the maꢀi-
mum peak-to-peak ripple on the inductor current (DIL).
The recommended peak-to-peak ripple is 603 of the
average inductor current.
Use the following equations to calculate the maꢀimum
average inductor current (IL
) and peak inductor
AVG
current (IL ) in amperes:
P
Power-Circuit Design
First select a converter topology based on the previous
factors. Determine the required input-supply voltage
range, the maꢀimum voltage needed to drive the LED
strings including the minimum 1V across the constant
I
LED
IL
=
AVG
1− D
MAX
Allowing the peak-to-peak inductor ripple DIL to be
+±03 of the average inductor current:
LED current sink (V ), and the total output current
LED
needed to drive the LED strings (I ) as follows:
LED
∆IL = IL
AVG
× 0.± × 2
I
= I
×N
STRING
LED
STRING
and:
where I
is the LED current per string in amperes
STRING
and N
is the number of strings used.
STRING
∆IL
2
Calculate the maꢀimum duty cycle (D ) using the
MAX
following equations:
IL = IL
+
AVG
P
For boost configuration:
Calculate the minimum inductance value, L
, in
MIN
henries with the inductor current ripple set to the maꢀi-
mum value:
(V
+ V − V
)
LED
D1
IN_MIN
D
=
MAX
(V
+ V − V − 0.±V)
D1 DS
LED
(VIN
− V − 0.±V)×D
DS MAX
MIN
L
=
For SEPIC and coupled-inductor boost-buck configura-
tions:
MIN
f
× ∆IL
SW
where 0.±V is the peak current-sense voltage. Choose
an inductor that has a minimum inductance greater than
(V
+ V
)
LED
D1
D
=
MAX
(V
− V − 0.±V + V
+ V )
IN_MIN
DS
LED D1
the calculated L
and current rating greater than IL .
MIN
P
The recommended saturation current limit of the selected
inductor is 103 higher than the inductor peak current
for boost configuration. For the coupled-inductor boost-
buck, the saturation limit of the inductor with only one
where V
volts (approꢀimately 0.6V), V
supply voltage in volts, and V
voltage of the eꢀternal MOSFET in volts when it is on,
and 0.±V is the peak current-sense voltage. Initially, use
is the forward drop of the rectifier diode in
D1
is the minimum input
is the drain-to-source
IN_MIN
DS
winding conducting should be 103 higher than IL .
P
SEPIC Configuration
an approꢀimate value of 0.2V for V to calculate D
.
DS
MAX
Power circuit design for the SEPIC configuration is very
similar to a conventional boost-buck 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 (see Figure 5 for the SEPIC
configuration). One of the inductors (L2) takes LED
current as the average current and the other (L1) takes
input current as the average current.
Calculate a more accurate value of D
MOSFET is selected based on the maꢀimum inductor
current. Select the switching frequency (f ) depending
on the space, noise, and efficiency constraints.
after the power
MAX
SW
Inductor Selection
Boost and Coupled-Inductor Boost-Buck
Configurations
In all the three converter configurations, the average
inductor current varies with the line voltage and the
Maxim Integrated
│ 16
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Use the following equations to calculate the average
The combined inductance value and current is calcu-
inductor currents (IL1
, IL2
AVG
) and peak inductor
AVG
lated as follows:
currents (IL1 IL2 ) in amperes:
P,
P
L1
×L2
+ L2
MIN
MIN
MIN
L
=
MIN
I
×D
×1.1
MAX
LED
L1
MIN
IL1
=
AVG
1− D
MAX
and:
where IL
IL
= IL1
+IL2
AVG
AVG
AVG
The factor 1.1 provides a 103 margin to account for the
converter losses:
represents the total average current through
AVG
both the inductors together for SEPIC configuration. Use
these values in the calculations for SEPIC configuration
in the following sections.
IL2
= I
AVG LED
Assuming the peak-to-peak inductor ripple DIL is Q±03
of the average inductor current:
Select coupling capacitor C so that the peak-to-
S
peak ripple on it is less than 23 of the minimum input
supply voltage. This ensures that the second-order
effects created by the series resonant circuit comprising
∆IL1= IL1
× 0.± × 2
AVG
and:
and:
L1, C , and L2 does not affect the normal operation of
S
the converter. Use the following equation to calculate the
minimum value of C :
S
∆IL1
2
IL1 = IL1
+
P
AVG
I
×D
MAX
× 0.02 × f
LED
C
≥
S
V
IN_MIN
SW
∆IL2 = IL2
× 0.± × 2
AVG
where C is the minimum value of the coupling capacitor
S
in farads, I
is the LED current in amperes, and the
LED
∆IL2
2
IL2 = IL2
+
factor 0.02 accounts for 23 ripple.
P
AVG
Slope Compensation
Calculate the minimum inductance values L1
and
MIN
The MAX16814 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 and rises linearly to
reach 50FA at the end of the clock cycle. The slope-
L2
in henries with the inductor current ripples set to
MIN
the maꢀimum value as follows:
(VIN − V − 0.±V)×D
MAX
MIN
DS
L1
=
MIN
f
× ∆IL1
compensating resistor, R , is connected between
SCOMP
SW
the CS input and the source of the eꢀternal MOSFET.
This adds a programmable ramp voltage to the CS input
voltage to provide slope compensation.
(VIN
− V − 0.±V)×D
MIN
DS MAX
L2
=
MIN
f
× ∆IL2
SW
Use the following equation to calculate the value of slope
where 0.±V is the peak current-sense voltage. Choose
inductors that have a minimum inductance greater than
compensation resistance (R
).
SCOMP
For boost configuration:
the calculated L1
and L2
and current rating
MIN
MIN
greater than IL1 and IL2 , respectively. The recom-
mended saturation current limit of the selected inductor
is 103 higher than the inductor peak current:
P
P
V
−2V
IN_MIN
×R × ±
(
=
)
LED
CS
× 4
R
SCOMP
L
× 50FA× f
SW
MIN
For simplifying further calculations, consider L1 and L2
as a single inductor with L1 and L2 connected in parallel.
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
External MOSFET Selection
For SEPIC and coupled-inductor boost-buck:
The eꢀternal MOSFET should have a voltage rating
sufficient to withstand the maꢀimum output voltage
together with the rectifier diode drop and any
possible overshoot due to ringing caused by parasitic
V
×R × ±
LED− VIN_MIN
CS
(
=
)
R
SCOMP
L
× 50FA× f
× 4
MIN
SW
inductances and capacitances. The recommended
and R
SCOMP CS
where V
are in ohms, L
and V
MIN
are in volts, R
LED
IN_MIN
MOSFET V
voltage rating is ±03 higher than the sum
DS
is in henries and f
is in hertz.
SW
of the maꢀimum output voltage and the rectifier diode
drop.
The value of the switch current-sense resistor, R , can
CS
be calculated as follows:
The recommended continuous drain current rating of the
MOSFET (ID), when the case temperature is at +70NC, is
greater than that calculated below:
For boost:
D
(
× V
(
− 2V
×R ×±
CS
)
)
MAX
LED
4×L
IN_MIN
0.±96×0.9 = I ×R
CS
+
LP
2
×f
MN SW
ID
=
IL
×D
×1.±
RMS
AVG
MAX
For SEPIC and boost-buck:
The MOSFET dissipates power due to both switching
losses and conduction losses. Use the following equa-
tion to calculate the conduction losses in the MOSFET:
D
(
× V
(
− V
IN_MIN
×R ×±
CS
)
)
MAX
LED
4×L
0.±96×0.9 = I ×R
CS
+
LP
×f
MN SW
2
P
= IL
×D
×R
MAX DS(ON)
where 0.±96 is the minimum value of the peak cur-
rent-sense threshold. The current-sense threshold also
includes the slope compensation component. The mini-
mum current-sense threshold of 0.±96 is multiplied by
0.9 to take tolerances into account.
COND
AVG
where R
is the on-state drain-to-source resistance
DS(ON)
of the MOSFET.
Use the following equation to calculate the switching
losses in the MOSFET:
Output Capacitor Selection
For all the three converter topologies, the output capaci-
tor 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 MAX16814, limit
the peak-to-peak output voltage ripple to 200mV to get
stable output current.
2
IL
× V
× C × f
GD SW
1
1
AVG
LED
P
=
×
+
SW
2
I
I
GOFF
GON
where I
and I
are the gate currents of the
GON
GOFF
MOSFET in amperes, when it is turned on and turned
off, respectively. C is the gate-to-drain MOSFET
GD
capacitance in farads.
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 203 higher
than the maꢀimum boost-converter output voltage and
current rating greater than that calculated in the follow-
ing equation:
The ESR, ESL, and the bulk capacitance of the output
capacitor contribute to the output ripple. In most of the
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 tantalum capacitor provides most of the
bulk capacitance.
I
= IL
× (1− D ) ꢀ 1.2
MAX
D
AVG
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Feedback Compensation
For SEPIC and coupled-inductor boost-buck configurations:
During normal operation, the feedback control loop
regulates the minimum OUT_ voltage to 1V 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 compensation capaci-
tor voltage. For the MAX16814A_ _ and the MAX16814U_
_, when the PWM dimming pulses are less than or equal
to 5 switching clock cycles, the feedback loop regulates
the converter output voltage to 953 of OVP threshold.
I
×D
LED
MAX
f
=
P1
2 × π × V
× C
LED
OUT
where f is in hertz, V
is in volts, I
is in amperes,
P1
OUT
LED
LED
and C
is in farads.
Compensation components (R
perform two functions. C
and C
)
COMP
COMP
introduces a low-
COMP
frequency pole that presents a -20dB/decade slope
to the loop gain. R flattens the gain of the error
COMP
amplifier for frequencies above the zero formed by
and C . For compensation, this zero is
placed at the output pole frequency f so that it pro-
vides a -20dB/decade slope for frequencies above f
to the combined modulator and compensator response.
The worst-case condition for the feedback loop is when
the LED driver is in normal mode regulating the minimum
OUT_ voltage to 1V. The switching converter small-signal
transfer function has a right-half plane (RHP) zero for
boost configuration if the inductor current is in continuous
conduction mode. The RHP zero adds a 20dB/decade
gain together with a 90N-phase lag, which is difficult to
compensate.
R
COMP
COMP
P1
P1
The value of R needed to fiꢀ the total loop gain
COMP
at f
so that the total loop gain crosses 0dB with
-20dB/decade slope at 1/5 the RHP zero frequency is
calculated as follows:
P1
The worst-case RHP zero frequency (f
calculated as follows:
) is
ZRHP
For boost configuration:
For boost configuration:
f
×R
×I
CS LED
ZRHP
R
=
COMP
5 × f × GM
× V
× (1 −D
)
MAX
P1
COMP
LED
2
V
(1− D
2π ×L ×I
)
LED
MAX
LED
f
=
ZRHP
For SEPIC and coupled-inductor boost-buck
configurations:
For SEPIC and coupled-inductor boost-buck
configurations:
f
×R
×I
×D
ZRHP
5 × f × GM
CS LED MAX
R
=
COMP
× V
×(1 −D
)
MAX
P1
COMP
LED
2
V
(1− D
)
MAX
LED
f
=
ZRHP
2π ×L ×I
×D
where
ohms, f
R
is the compensation resistor in
and f are in hertz, R is the switch
P2
COMP
ZRHP
LED
MAX
CS
where f
is in hertz, V
is in volts, L is the induc-
LED
ZRHP
current-sense resistor in ohms, and GM
transconductance of the error amplifier (600FS).
is the
COMP
tance value of L1 in henries, and I
is in amperes. A
LED
simple way to avoid this zero is to roll off the loop gain
to 0dB at a frequency less than one fifth of the RHP zero
frequency with a -20dB/decade slope.
The value of C
is calculated as follows:
COMP
1
C
=
COMP
The switching converter small-signal transfer function
also has an output pole. The effective output impedance
together with the output filter capacitance determines the
2π ×R
× f
COMP Z1
where f
is the compensation zero placed at 1/5 of
the crossover frequency that is, in turn, set at 1/5 of the
Z1
output pole frequency f that is calculated as follows:
P1
For boost configuration:
f
.
ZRHP
I
LED
f
=
P1
2 × π × V
× C
OUT
LED
Maxim Integrated
│ 19
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
If the output capacitors do not have low ESR, the ESR
zero frequency may fall within the 0dB crossover fre-
quency. An additional pole may be required to cancel
out this pole placed at the same frequency. This is
usually implemented by connecting a capacitor in paral-
multiplied by a factor of 1220 is the current through
each one of the four constant current-sink channels.
Adjust the current through SETI to get analog dimming
functionality by connecting the eꢀternal control voltage
to SETI through the resistor R
. The resulting change
SETI2
lel with C
and R
. Figure 5 shows the SEPIC
in the LED current with the control voltage is linear and
inversely proportional. The LED current control range
remains between 20mA to 150mA.
COMP
COMP
configuration and Figure 6 shows the coupled-inductor
boost-buck configuration.
Use the following equation to calculate the LED current
set by the control voltage applied:
Analog Dimming Using External
Control Voltage
Connect a resistor R
to the SETI input as shown
SETI2
1.2± − V
(
)
×1220
1500
C
in Figure 7 for controlling the LED string current using
an eꢀternal control voltage. The MAX16814 applies a
fiꢀed 1.2±V bandgap reference voltage at SETI and
measuresthecurrentthroughSETI.Thismeasuredcurrent
I
=
+
OUT
R
R
SETI2
SETI
V
IN
4.75V TO 40V
C
D1
S
L1
UP TO 40V
C1
C2
R1
R2
N
L2
R
R
CS
SCOMP
IN
NDRV
CS
OVP
EN
V
OUT1
OUT2
OUT3
OUT4
CC
C3
MAX16814
R5
C4
DRV
R
SETI
SETI
FLT
V
CC
DIM
R3
COMP
RSDT
RT
R
COMP
R4
SGND
PGND
LEDGND
R
T
C
COMP
Figure 5. SEPIC Configuration
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│ 20
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
PCB Layout Considerations
±) 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
LED driver circuits based on the MAX16814 device use
a high-frequency switching converter to generate the
voltage for LED strings. Take proper care while laying
out the circuit to ensure proper operation. The switching-
converter part 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:
1) Connect the bypass capacitor on V
and DRV as
CC
areas as small as possible. Wherever possible, have a
return path on the power ground plane for the switch-
ing currents on the top layer copper traces, or through
power components. This reduces the loop area con-
siderably and provides a low-inductance path for
the switching currents. Reducing the loop area also
reduces radiation during switching.
close to the device as possible and connect the
capacitor ground to the analog ground plane using
vias close to the capacitor terminal. Connect SGND
of the device to the analog ground plane using a via
close to SGND. Lay the analog ground plane on the
inner layer, preferably neꢀt to the top layer. Use the
analog ground plane to cover the entire area under
critical signal components for the power converter.
4) Connect the power ground plane for the constant-
current LED driver part of the circuit to LEDGND as
close to the device as possible. Connect SGND to
PGND at the same point.
2) Have a power ground plane for the switching-
converter power circuit under the power components
(input filter capacitor, output filter capacitor, inductor,
MOSFET, rectifier diode, and current-sense resis-
tor). Connect PGND to the power ground plane as
close to PGND as possible. Connect all other ground
connections to the power ground plane using vias
close to the terminals.
Maxim Integrated
│ 21
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
V
IN
4.75V TO 40V
T1
(1:1)
D1
C1
UP TO 40V
C2
R1
R2
N
R
R
CS
SCOMP
IN
NDRV
CS
OVP
OUT1
EN
V
OUT2
OUT3
OUT4
CC
C3
MAX16814
R5
C4
DRV
R
SETI
SETI
FLT
V
CC
DIM
R3
COMP
RSDT
RT
R
COMP
R4
SGND
PGND
LEDGND
R
T
C
COMP
Figure 6. Coupled-Inductor Boost-Buck Configuration
MAX16814
R
SETI2
SETI
1.23V
R
V
C
SETI
Figure 7. Analog Dimming with External Control Voltage
Maxim Integrated
│ 22
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Typical Operating Circuit
V
IN
4.75V TO 40V
D1
L
UP TO 40V
C1
C2
R1
R2
N
R
R
CS
SCOMP
IN
NDRV
CS
OVP
EN
V
OUT1
OUT2
OUT3
OUT4
CC
C3
MAX16814
R5
C4
DRV
R
SETI
SETI
FLT
V
CC
DIM
R3
COMP
RSDT
RT
R
COMP
R4
SGND
PGND
LEDGND
R
T
C
COMP
Maxim Integrated
│ 23
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Ordering Information
Chip Information
PROCESS: BiCMOS DMOS
PART
TEMP RANGE
-40°C to +125°C
PIN-PACKAGE
20 TQFN-EP*
20 TQFN-EP*
MAX16814ATP+
MAX16814ATP/V+ -40°C to +125°C
MAX16814AGP/VY+ -40°C to +125°C
20 QFND-EP* (SW)
20 TSSOP-EP*
20 TSSOP-EP*
20 TQFN-EP*
Package Information
MAX16814AUP+
MAX16814AUP/V+ -40°C to +125°C
MAX16814BETP+ -40°C to +85°C
MAX16814BEUP+ -40°C to +85°C
-40°C to +125°C
For the latest package outline information and land patterns, 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.
20 TSSOP-EP*
20 TQFN-EP*
MAX16814BUTP+
MAX16814BUUP+
MAX16814UTP+
MAX16814UUP+
0°C to +85°C
0°C to +85°C
0°C to +85°C
0°C to +85°C
20 TSSOP-EP*
20 TQFN-EP*
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE LAND PATTERN
NO.
NO.
20 TSSOP-EP*
20 TSSOP-EP
20 TQFN-EP
U20E+1
21-0108
21-0139
90-0114
90-0037
T2044+3
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
/V denotes an automotive qualified part; (SW) = side wettable.
20 QFND-EP
(Side Wettable)
G2044Y+1
21-0576
90-0360
Maxim Integrated
│ 24
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MAX16814
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Revision History
REVISION
NUMBER
REVISION
DATE
DESCRIPTION
PAGES CHANGED
0
1
7/09
Initial release
—
9/09
Correction to slope compensation description and block diagram
10, 18
Correction to synchronization description frequency and minor
edits
2
11/09
1–4, 8, 12–20, 22, 25
3
4
2/10
6/10
Correction to CSYNC formula
13
Added MAX16814BE _ _ parts; corrected specification
1–4, 8, 13, 25
Correction to output current accuracy specification and Absolute
Maximum Ratings
5
6
3/11
1, 2, 4
19
10/11
Correction to the last formula and description
Added side-wettable package option and updated EN leakage in
Electrical Characteristics
7
8
1/13
4/13
1, 2, 4, 8, 9, 23, 24
10, 11, 14, 18, 19
Minor corrections to Figures 1, 2, and the LED Diming Control,
Rectifier Diode Selection, and Feedback Compensation sections
9
11/13
2/15
Corrected V
offset voltage in Figure 1
10
1
COMP
10
11
Updated the Benefits and Features section
Updated the LED Dimming Control section
3/16
14
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
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.
2016 Maxim Integrated Products, Inc.
│ 25
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