MAX16814ATP/V [MAXIM]
LED Driver, 28-Segment, BCDMOS, 4 X 4 MM, TQFN-20;
| 型号： | MAX16814ATP/V |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | LED Driver, 28-Segment, BCDMOS, 4 X 4 MM, TQFN-20 驱动器 高压 控制器 |
| 文件： | 总25页 (文件大小：1996K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-4722; Rev 5; 3/11
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
General Description
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 pro-
vides the necessary voltage to multiple strings of HB
LEDs. The MAX16814 accepts a wide 4.75V to 40V input
voltage range and withstands direct automotive load-
dump events. The wide input range allows powering HB
LEDs for small to medium-sized LCD displays in automo-
tive and general lighting applications.
S 4-Channel Linear LED Current Sinks with Internal
MOSFETs
Full-Scale LED Current Adjustable from 20mA
to 150mA
Drives One to Four LED Strings
S Boost, SEPIC, or Coupled-Inductor Boost-Buck
Current-Mode DC-DC Controller
200kHz to 2MHz Programmable Switching
Frequency
An internal current-mode switching DC-DC controller
supports the boost, coupled-inductor boost-buck, or
SEPIC topologies and operates in an adjustable fre-
quency range between 200kHz and 2MHz. It can also be
used for single-inductor boost-buck topology in conjunc-
tion with the MAX15054 and an additional MOSFET. The
current-mode control with programmable slope com-
pensation 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.
External Switching Frequency Synchronization
S Adaptive Output-Voltage Optimization to Minimize
Power Dissipation
S 4.75V to 40V Operating Input Voltage Range
S Less than 40µA Shutdown Current
S 5000:1 PWM Dimming at 200Hz (MAX16814A _ _
and MAX16814U_ _ Only)
S Open-Drain Fault Indicator Output
S Open-LED and LED Short Detection and
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 external resistor. The
external 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.
Protection
S Overtemperature Protection
S Thermally Enhanced, 20-Pin TQFN and TSSOP
Packages
Ordering Information
PART
TEMP RANGE
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
PIN-PACKAGE
20 TQFN-EP*
20 TQFN-EP*
20 TSSOP-EP*
20 TSSOP-EP*
20 TQFN-EP*
20 TSSOP-EP*
20 TQFN-EP*
20 TSSOP-EP*
20 TQFN-EP*
20 TSSOP-EP*
MAX16814ATP+
MAX16814ATP/V+
MAX16814AUP+
The MAX16814 includes an output overvoltage, open-
LED detection and protection, programmable shorted
LED detection and protection, and overtemperature pro-
tection. The device operates over the -40NC to +125NC
automotive temperature range. The MAX16814 is avail-
able in 6.5mm x 4.4mm, 20-pin TSSOP and 4mm x 4mm,
20-pin TQFN packages.
MAX16814AUP/V+ -40°C to +125°C
MAX16814BETP+
MAX16814BEUP+
MAX16814BUTP+
MAX16814BUUP+
MAX16814UTP+
MAX16814UUP+
-40°C to +85°C
-40°C to +85°C
0°C to +85°C
0°C to +85°C
0°C to +85°C
0°C to +85°C
Applications
Automotive Displays LED Backlights
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
/V Denotes an automotive qualified part.
Automotive RCL, DRL, Front Position, and Fog
Lights
LCD TV and Desktop Display LED Backlights
Architectural, Industrial, and Ambient Lighting
Typical Operating Circuit and Pin Configurations appear at
end of data sheet.
_______________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
ABSOLUTE MAXIMUM RATINGS
IN to SGND............................................................-0.±V to +45V
V
CC
Short-Circuit Duration........................................Continuous
EN to SGND ...............................................-0.±V to (V + 0.±V)
Continuous Power Dissipation (T = +70NC) (Note 1)
IN
A
PGND to SGND....................................................-0.±V to +0.±V
LEDGND to SGND ...............................................-0.±V to +0.±V
OUT_ to LEDGND .................................................-0.±V to +45V
20-Pin TQFN (derate 25.6mW/NC above +70NC).......2051mW
26-Pin TSSOP (derate 26.5mW/NC above +70NC).....2122mW
Operating Temperature Range
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
V
to SGND ..........-0.±V to the lower of (V + 0.±V) and +6V
CC
IN
DRV, FLT, DIM, RSDT, OVP to SGND.....................-0.±V to +6V
CS, RT, COMP, SETI to SGND................. -0.±V to (V
NDRV to PGND .......................................-0.±V to (V
NDRV Peak Current (< 100ns)............................................. Q±A
NDRV Continuous Current ............................................ Q100mA
OUT_ Continuous Current............................................. Q175mA
+ 0.±V)
+ 0.±V)
CC
DRV
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 THERMAL CHARACTERISTICS (Note 1)
20 TQFN
20 TSSOP
Junction-to-Ambient Thermal Resistance (B )........ +±9NC/W
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.maxim-ic.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
IN
4.75
V
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
V
= 0V
µA
V
EN
IN
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
2
______________________________________________________________________________________
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
Maximum 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 x 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, excluding 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
= 5V
A
A
NDRV
NDRV
V
= 0V
C
C
= 1nF
= 1nF
ns
ns
LOAD
Fall Time
6
LOAD
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
_______________________________________________________________________________________
3
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
DIM
= 0V, V = 40V
1
µA
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 Reference Voltage
EN Hysteresis
V
EN
MAX16814B_ _ _
mV
nA
V
V
= 40V, MAX16814A_ _ only
= 40V, MAX16814U_ _ and
±200
±250
EN
EN Input Current
EN
MAX16814B_ _ _
DIM Input High Voltage
DIM Input Low Voltage
DIM Hysteresis
2.1
V
V
0.8
±2
250
mV
µA
ns
ns
ns
V
DIM Input Current
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_
V
V
= 4.75V and I
= 5mA
SINK
0.4
1.0
FLT Output Low Voltage
IN
µA
V
= 5.5V
FLT Output Leakage Current
LED Short Detection Threshold
Short Detection Comparator Delay
RSDT Leakage Current
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
4
______________________________________________________________________________________
Integrated, 4-Channel, High-Brightness LED Driver
with High-Voltage Boost and SEPIC Controller
Typical Operating Characteristics
(V = V = 12V, f
= ±00kHz, R
= 15kI, C
= 1FF, V
= V
, NDRV = COMP = OUT_ = unconnected, V
= V
=
IN
EN
SW
SETI
VCC
CC
DRV
OVP
CS
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
C
4.2
310
= 13pF
NDRV
308
306
304
302
300
298
296
294
292
290
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)
_______________________________________________________________________________________
5
Integrated, 4-Channel, High-Brightness LED Driver
with High-Voltage Boost and SEPIC Controller
Typical Operating Characteristics (continued)
(V = V = 12V, f
= ±00kHz, R
= 15kI, C
= 1FF, V
= V
, NDRV = COMP = OUT_ = unconnected, V
= V
=
IN
EN
SW
SETI
VCC
CC
DRV
OVP
CS
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)
6
______________________________________________________________________________________
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
= V
CS
=
IN
EN
SW
SETI
VCC
CC
DRV
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
OUT1
V
DIM
5V/div
0V
100mA/div
0A
I
OUT2
100mA/div
0A
I
OUT3
I
LED
100mA/div
0A
50mA/div
0A
I
OUT4
100mA/div
0A
FIGURE 2
100Fs/div
4Fs/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
SETI
(mS)
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)
_______________________________________________________________________________________
7
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Pin Description
PIN
TSSOP
NAME
IN
FUNCTION
TQFN
Bias Supply Input. Connect a 4.75V to 40V supply to IN. Bypass IN to SGND with a ceramic
capacitor.
1
4
5
6
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.
2
±
EN
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 x 10 /f (for the MAX16814A_ _
T
sw
4
7
RT
9
and the MAX16814U_ _) or to the formula R = 7.72 x 10 /f (for the
an
MAX16814B_ _ _). Apply
T
sw
AC-coupled external clock at RT to synchronize the switching frequency with an external 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
11
RSDT
SGND to program the LED short detection threshold. Connect RSDT directly to V
to disable
CC
LED short detection. The LED short detection comparator is internally referenced to 2V.
Signal Ground. SGND is the current return path connection for the low-noise analog signals.
Connect SGND, LEDGND, and PGND at a single point.
9
12
1±
SGND
DIM
Digital PWM Dimming Input. Apply a PWM signal to DIM for LED dimming control. Connect
10
DIM 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
8
______________________________________________________________________________________
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Pin Description (continued)
PIN
TSSOP
NAME
OUT2
FUNCTION
TQFN
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
15
16
17
LED Ground. LEDGND is the return path connection for the linear current sinks. Connect
SGND, LEDGND, and PGND at a single point.
1±
14
LEDGND
OUT±
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 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 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 external 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
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 SGND.
—
EP
_______________________________________________________________________________________
9
Integrated, 4-Channel, High-Brightness LED Driver
with High-Voltage Boost and SEPIC Controller
FLT
RSDT
V
REF
POKD
UNUSED
STRING
DETECTOR
MAX16814
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
1.8V
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
10 _____________________________________________________________________________________
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
COMP
R
CS
IN
NDRV
CS
OVP
EN
OUT1
OUT2
V
CC
C3
OUT3
OUT4
R5
MAX16814
VDRV
C4
R
SETI
SETI
FLT
V
CC
DIM
R6
R3
COMP
RSDT
RT
R4
R
COMP
R
T
C
COMP
SGND
PGND
LEDGND
Figure 2. Circuit Used for Typical Operating Characteristics
______________________________________________________________________________________ 11
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Shorted LED string detection and overvoltage protec-
tion thresholds are programmable using RSDT and OVP
inputs, respectively. An open-drain FLT signal asserts to
Detailed Description
The MAX16814 high-efficiency HB LED driver inte-
grates all the necessary features to implement a high-
indicate open-LED, shorted LED, and overtemperature
performance backlight driver to power LEDs in small
conditions. Disable individual current-sink channels by
to medium-sized displays for automotive as well as
general applications. The device provides load-dump
voltage protection up to 40V in automotive applications.
connecting the corresponding OUT_ to LEDGND. In this
case, FLT does not assert indicating an open-LED con-
dition for the disabled channel. The device also features
The MAX16814 incorporates two major blocks: a DC-DC
an overtemperature protection that shuts down the con-
controller with peak current-mode control to implement
a boost, coupled-inductor boost-buck, or a SEPIC-type
troller if the die temperature exceeds +165NC.
Current-Mode DC-DC Controller
The peak current-mode controller allows boost, coupled-
inductor buck-boost, or SEPIC-type converters to gener-
ate the required bias voltage for the LED strings. The
switching frequency can be programmed over the 200kHz
to 2MHz range using a resistor connected from RT to
SGND. Programmable slope compensation is available
to compensate for subharmonic oscillations that occur at
above 503 duty cycles in continuous conduction mode.
switched-mode power supply and a 4-channel LED driv-
er with 20mA to 150mA constant current-sink capability
per channel. Figure 1 is the simplified functional diagram
and Figure 2 shows the circuit used for typical operating
characteristics.
The MAX16814 features a constant-frequency peak
current-mode control with programmable slope com-
pensation to control the duty cycle of the PWM control-
ler. The high-current FET driver can provide up to 2A of
current to the external 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 external 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 external MOSFET to
PGND. The MAX16814 features leading-edge blanking to
suppress the external MOSFET switching noise. A PWM
comparator compares the current-sense voltage plus the
slope compensation signal with the output of the transcon-
ductance error amplifier. The controller turns off the exter-
nal MOSFET when the voltage at CS exceeds 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
powering additional external 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
minimum string detector measures the minimum current-
sink voltage with respect to SGND out of the 4 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 ampli-
fied 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-dis-
connect 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 condition.
12 _____________________________________________________________________________________
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
The converter stops switching when the LED strings are
turned off during PWM dimming. The error amplifier is
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.
soft-start, the DC-DC converter output ramps towards
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
The internal oscillator frequency is programmable
Undervoltage Lockout (UVLO)
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
below to calculate the value of R for the desired switch-
T
nal LDO regulator at V . The device turns on after both
ing frequency, f
.
CC
SW
V
and V
exceed their respective UVLO thresholds.
IN
CC
9
7.±5×10 Hz
The UVLO threshold at IN is 4.±V when V is rising and
4.15V when V is falling. The UVLO threshold at V
is 4V when V
IN
R
=
T
f
IN
CC
SW
is rising and ±.9V when V
is falling.
CC
CC
(for the MAX16814A_ _ and the MAX16814U_ _).
Enable
9
7.72 ×10
EN is a logic input that completely shuts down the
device when connected to logic-low, reducing the cur-
rent consumption of the device to less than 40FA. The
logic threshold at EN is 1.2±V (typ). The voltage at EN
must exceed 1.2±V before any operation can com-
mence. There is a 50mV hysteresis on EN. The EN input
also allows programming the supply input UVLO thresh-
old using an external voltage-divider to sense the input
voltage as shown below.
R
=
T
f
SW
(for the MAX16814B_ _ _).
Synchronize the oscillator with an external clock by
AC-coupling the external 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
V
IN
where V
is the desired undervoltage lockout level
UVLO
R1
R2
MAX16814
and 1.2±V is the EN input reference. Connect EN to IN
if not used.
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
1.23V
Figure 3. Setting the MAX16814 Undervoltage Lockout
Threshold
______________________________________________________________________________________ 13
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
where R is in Ω.
T
R
= 1500 I
SETI
OUT_
The pulse width for the synchronization pulse should
satisfy the following relations:
where I
four channels.
is the desired output current for each of the
OUT_
t
PW
V < 0.5
S
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.
t
CLK
t
PW
0.8 −
V
+ V > ±.4
S
S
t
CLK
LED Dimming Control
The MAX16814 features LED brightness control using an
external 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.
t
CLK
t
<
t
− 1.05×t
CLK
(
)
PW
CI
t
CI
where t
is the synchronization source pulse width,
PW
t
is the synchronization clock time period, t
CLK
CI is the
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 5 oscillator clock cycles
(DIM pulse width decreasing) then the boost converter
regulates its output based on feedback 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.
V
is the synchronization
programmed clock period, and
pulse voltage level.
S
5V LDO Regulator (V
The internal LDO regulator converts the input voltage
at IN to a 5V output voltage at V . The LDO regulator
supplies up to 50mA current to provide power to internal
control circuitry and the gate driver. Connect a resistor
and DRV to power the gate-drive circuitry;
the recommended value is 4.7I. Bypass DRV with a
capacitor to PGND. The external resistor and bypass
capacitor provide noise filtering. Bypass V
)
CC
CC
between V
CC
to SGND
CC
with a minimum of 1FF ceramic capacitor as close to the
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
device as possible.
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 external 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.
BOOST CONVERTER
OUTPUT
The power dissipation in the MAX16814 is mainly a func-
tion of the average current sourced to drive the external
MOSFET (I
) if there are no additional loads on V
.
DRV
CC
40mA TO 300mA
PER STRING
I
depends on the total gate charge (Q ) and operat-
DRV
G
ing frequency of the converter. Connect DRV to V
with
CC
a 4.7I resistor to power the gate driver with the internal
5V regulator.
OUT1
OUT2
OUT3
OUT4
MAX16814
LED Current Control
The MAX16814 features four identical constant-current
sources used to drive multiple HB LED strings. The cur-
rent through each one of the four channels is adjustable
between 20mA and 150mA using an external resistor
(R
R
) connected between SETI and SGND. Select
using the following formula:
SETI
SETI
Figure 4. Configuration for Higher LED String Current
14 _____________________________________________________________________________________
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Short LED Detection
The MAX16814 checks for shorted LEDs at each rising
edge of DIM. An LED short is detected at OUT_ if the
following condition is met:
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 condi-
tion 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.
V
OUT_
> V + ± x V
MINSTR RSDT
where V
is the voltage at OUT_, V
is the
MINSTR
OUT_
minimum current-sink voltage, and V
is the pro-
RSDT
grammable LED short detection threshold set at the
RSDT input. Adjust V using a voltage-divider resis-
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 chan-
nels. 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 mini-
mum OUT_ voltage as the feedback input. If any LED
string is open, the voltage at the opened OUT_ goes
RSDT
tive network connected at the V
and SGND.
output, RSDT input,
CC
Once a short is detected on any of the strings, the LED
strings with the short are disconnected and the FLT out-
put 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.
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 con-
stant current-sink drivers. If the LED string forward volt-
age is always more than the input supply voltage range,
use the boost converter topology. If the LED string for-
ward 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
where 1.2±V (typ) is the OVP threshold. Select R1 and
R2 such that the voltage at OUT_ does not exceed the
absolute maximum rating. As soon as the DC-DC con-
verter output reaches the overvoltage protection thresh-
old, the PWM controller is switched off setting NDRV
The boost converter topology provides the highest
efficiency among the above mentioned topologies. The
coupled-inductor boost-buck topology has the advan-
tage of not using a coupling capacitor over the SEPIC
configuration. Also, the feedback loop compensation for
SEPIC becomes complex 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.
low. Any current-sink output with V
disconnected from the minimum voltage detector.
< ±00mV (typ) is
OUT_
Connect the OUT_ of all channels without LED connec-
tions to LEDGND before power-up to avoid OVP trigger-
ing at startup. When an open-LED overvoltage condition
occurs, FLT is latched low.
______________________________________________________________________________________ 15
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Use the following equations to calculate the maximum
Power-Circuit Design
First select a converter topology based on the above
factors. Determine the required input supply voltage
range, the maximum voltage needed to drive the LED
strings including the minimum 1V across the constant
average inductor current (IL ) and peak inductor cur-
AVG
rent (IL ) in amperes:
P
I
LED
IL
=
AVG
LED current sink (V ), and the total output current
LED
1− D
MAX
needed to drive the LED strings (I ) as follows:
LED
Allowing the peak-to-peak inductor ripple DIL to be
+±03 of the average inductor current:
I
= I
×N
STRING STRING
LED
where I
is the LED current per string in amperes
is the number of strings used.
STRING
∆IL = IL
× 0.± × 2
AVG
and N
STRING
and:
Calculate the maximum duty cycle (D ) using the fol-
MAX
lowing equations:
∆IL
2
For boost configuration:
IL = IL
+
AVG
P
(V
+ V − V
)
LED
D1
IN_MIN
D
=
Calculate the minimum inductance value, L
ries with the inductor current ripple set to the maximum
value:
, in hen-
MAX
MIN
(V
+ V − V − 0.±V)
D1 DS
LED
For SEPIC and coupled-inductor boost-buck-configura-
tions:
(VIN
− V − 0.±V)×D
DS MAX
MIN
L
=
MIN
(V
+ V
)
f
× ∆IL
LED
D1
SW
D
=
MAX
(V
− V − 0.±V + V
+ V )
IN_MIN
DS
LED D1
where 0.±V is the peak current-sense voltage. Choose
an inductor that has a minimum inductance greater
and current rating greater than
IL . 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
where V
is the forward drop of the rectifier diode in
D1
than the calculated L
MIN
volts (approximately 0.6V), V
supply voltage in volts, and V
voltage of the external MOSFET in volts when it is on,
and 0.±V is the peak current-sense voltage. Initially, use
an approximate value of 0.2V for V to calculate D
is the minimum input
is the drain-to-source
IN_MIN
DS
P
.
DS
MAX
one winding conducting should be 103 higher than IL .
P
Calculate a more accurate value of D
after the power
MAX
MOSFET is selected based on the maximum inductor
SEPIC Configuration
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 cur-
rent as the average current and the other (L1) takes
input current as the average current.
current. Select the switching frequency (f ) depending
SW
on the space, noise, and efficiency constraints.
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
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 (DIL). The
recommended peak-to-peak ripple is 603 of the aver-
age inductor current.
Use the following equations to calculate the average
inductor currents (IL1 , IL2 ) and peak inductor
AVG AVG
currents (IL1 IL2 ) in amperes:
P,
P
I
×D
1− D
×1.1
MAX
LED
IL1
=
AVG
MAX
16 _____________________________________________________________________________________
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
The factor 1.1 provides a 103 margin to account for the
converter losses:
For simplifying 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 follows:
IL2
= I
AVG LED
Assuming the peak-to-peak inductor ripple DIL is Q±03
of the average inductor current:
L1
×L2
+ L2
MIN
MIN
MIN
L
=
MIN
L1
MIN
∆IL1= IL1
× 0.± × 2
AVG
and:
and:
and:
IL
= IL1
+IL2
AVG
AVG
AVG
∆IL1
2
where IL
represents the total average current through
AVG
IL1 = IL1
+
P
AVG
both the inductors together for SEPIC configuration. Use
these values in the calculations for SEPIC configuration
in the following sections.
∆IL2 = IL2
× 0.± × 2
AVG
Select coupling capacitor C so that the peak-to-peak
S
ripple on it is less than 23 of the minimum input sup-
ply voltage. This ensures that the second-order effects
created by the series resonant circuit comprising L1,
∆IL2
2
IL2 = IL2
+
AVG
P
C , and L2 does not affect the normal operation of the
S
converter. Use the following equation to calculate the
Calculate the minimum inductance values L1
and
MIN
minimum value of C :
S
L2
in henries with the inductor current ripples set to
MIN
the maximum value as follows:
I
×D
MAX
× 0.02 × f
LED
C
≥
S
V
(VIN
− V − 0.±V)×D
DS MAX
IN_MIN
SW
MIN
L1
=
MIN
f
× ∆IL1
SW
where C is the minimum value of the coupling capacitor
is the LED current in amperes, and the
factor 0.02 accounts for 23 ripple.
S
(VIN
− V − 0.±V)×D
MIN
DS MAX
L2
=
in farads, I
LED
MIN
f
× ∆IL2
SW
Slope Compensation
where 0.±V is the peak current-sense voltage. Choose
inductors that have a minimum inductance greater than
The MAX16814 generates a current ramp for slope com-
pensation. This ramp current is in sync with the switch-
ing 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-compensating resistor,
the calculated L1
and L2
and current rating
MIN
MIN
greater than IL1 and IL2 , respectively. The recom-
P
P
mended saturation current limit of the selected inductor
is 103 higher than the inductor peak current:
R
, is connected between the CS input and the
SCOMP
source of the external MOSFET. This adds a program-
mable ramp voltage to the CS input voltage to provide
slope compensation.
______________________________________________________________________________________ 17
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Use the following equation to calculate the value of slope
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.
compensation resistance, R
.
SCOMP
For boost configuration:
V
−2V
IN_MIN
×R × ±
(
=
)
External MOSFET Selection
The external MOSFET should have a voltage rating suf-
ficient to withstand the maximum output voltage together
with the rectifier diode drop and any possible overshoot
due to ringing caused by parasitic inductances and
LED
CS
× 4
R
SCOMP
L
× 50FA× f
SW
MIN
For SEPIC and coupled-inductor boost-buck:
LED− VIN_MIN
V
×R × ±
CS
(
=
)
capacitances. The recommended MOSFET V voltage
DS
R
SCOMP
rating is ±03 higher than the sum of the maximum output
voltage and the rectifier diode drop.
L
× 50FA× f
× 4
SW
MIN
The recommended continuous drain current rating of the
MOSFET (ID), when the case temperature is at +70NC, is
greater than that calculated below:
where V
are in ohms, L
and V
MIN
are in volts, R
and R
is in hertz.
LED
IN_MIN
SCOMP CS
is in henries and f
SW
The value of the switch current-sense resistor, R , can
CS
be calculated as follows:
2
ID
=
IL
×D
×1.±
RMS
AVG
MAX
For boost:
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
(
− 2V
×R ×±
CS
)
)
MAX
LED
4×L
IN_MIN
0.±96×0.9 = I ×R
CS
+
LP
×f
MN SW
For SEPIC and boost-buck:
2
P
= IL
×D
×R
MAX DS(ON)
COND
AVG
D
(
× V
(
− V
×R ×±
CS
)
)
MAX
LED
4×L
IN_MIN
where R
of the MOSFET.
is the on-state drain-to-source resistance
DS(ON)
0.±96×0.9 = I ×R
CS
+
LP
×f
MN SW
Use the following equation to calculate the switching
losses in the MOSFET:
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.
2
IL
× V
× C × f
GD SW
1
1
AVG
LED
P
=
×
+
SW
2
I
I
GOFF
GON
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.
where I
MOSFET in amperes, with V
in volts, when it is turned on and turned off, respectively.
and I
are the gate currents of the
GON
GOFF
at the threshold voltage
GS
C
GD
is the gate-to-drain MOSFET 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 maximum 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
1.2 ×IL
AVG
MAX
I
=
D
1− D
18 _____________________________________________________________________________________
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Feedback Compensation
During normal operation, the feedback control loop reg-
ulates 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 condi-
tion in the form of capacitor voltages, mainly the output
filter capacitor voltage and compensation capacitor
voltage. For the MAX16814A_ _ and the MAX16814U_
_, when the PWM dimming pulses are less than five
switching clock cycles, the feedback loop regulates the
converter output voltage to 953 of the OVP threshold.
For SEPIC and coupled-inductor boost-buck configurations:
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
LED
LED
and C
is in farads.
OUT
Compensation components, R
and C
, per-
COMP
COMP
form two functions. C
introduces a low-frequency
COMP
pole that presents a -20dB/decade slope to the loop
gain. R flattens the gain of the error amplifier for
COMP
frequencies above the zero formed by R
and
COMP
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.
C
. For compensation, this zero is placed at the
COMP
output pole frequency f so that it provides a -20dB/
decade slope for frequencies above f to the combined
modulator and compensator response.
P1
P1
The value of R
needed to fix the total loop gain at
COMP
f
so that the total loop gain crosses 0dB with -20dB/
P1
decade slope at 1/5 the RHP zero frequency is calcu-
lated as follows:
The worst-case RHP zero frequency (f ) is calcu-
ZRHP
lated as follows:
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 configura-
tions:
For SEPIC and coupled-inductor boost-buck configura-
tions:
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 R
is the compensation resistor in ohms,
COMP
LED
MAX
f
and f are in hertz, R
is the switch current-
ZRHP
P2
CS
where f
is in hertz, V
is in volts, L is the induc-
ZRHP
LED
sense resistor in ohms, and GM
ductance of the error amplifier (600FS).
is the transcon-
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 P1
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 usu-
ally implemented by connecting a capacitor in parallel
output pole frequency f that is calculated as follows:
P1
For boost configuration:
I
LED
f
=
P1
with C
and R
. Figure 5 shows the SEPIC
COMP
2 × π × V
× C
OUT
COMP
LED
configuration and Figure 6 shows the coupled-inductor
boost-buck configuration.
______________________________________________________________________________________ 19
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
SETI through the resistor R
. The resulting change
Analog Dimming Using External
Control Voltage
SETI2
in the LED current with the control voltage is linear and
inversely proportional. The LED current control range
remains between 20mA to 150mA.
Connect a resistor R
to the SETI input as shown in
SETI2
Figure 7 for controlling the LED string current using an
external control voltage. The MAX16814 applies a fixed
1.2±V bandgap reference voltage at SETI and measures
the current through SETI. This measured current mul-
tiplied 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 func-
tionality by connecting the external control voltage to
Use the following equation to calculate the LED current
set by the control voltage applied:
1.2± − V
(
)
×1220
1500
C
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
20 _____________________________________________________________________________________
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
±) 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 nega-
tive 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.
PCB Layout Considerations
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 volt-
age 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
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 next 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-con-
verter power circuit under the power components
(input filter capacitor, output filter capacitor, inductor,
MOSFET, rectifier diode, and current-sense resistor).
Connect PGND to the power ground plane as close
to PGND as possible. Connect all other ground con-
nections to the power ground plane using vias close
to the terminals.
______________________________________________________________________________________ 21
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
22 _____________________________________________________________________________________
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
8
RSDT
SETI
OVP
EN
COMP
RT
MAX16814
7
EP*
20
6
V
CC
FLT
1
2
3
4
5
OVP
12 SGND
11 RSDT
EP*
SETI 10
THIN QFN
TSSOP
*EXPOSED PAD.
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
Integrated, 4-Channel, High-Brightness LED
Driver with High-Voltage DC-DC Controller
Chip Information
Package Information
PROCESS: BiCMOS DMOS
For the latest package outline information and land patterns,
go to www.maxim-ic.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
TYPE
PACKAGE
CODE
OUTLINE LAND PATTERN
NO.
NO.
20 TSSOP-EP
20 TQFN-EP
U20E+1
T2044+±
21-0108
21-0139
90-0114
90-0037
24 _____________________________________________________________________________________
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
±
4
2/10
6/10
Correction to CSYNC formula
1±
Added MAX16814BE _ _ parts; corrected specification
1–4, 8, 1±, 25
Correction to output current accuracy specification and Absolute
Maximum Ratings
5
±/11
1, 2, 4
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.
Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
25
©
2011 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
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