EVALUATION KIT AVAILABLE
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
General Description
The MAX16813B high-efficiency, high-brightness LED
(HB LED) driver provides four integrated LED currentsink channels. An integrated current-mode switching
controller drives a DC-DC converter that provides the
necessary voltage to multiple strings of HB LEDs. The
device 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 automotive and general
lighting applications.
An internal current-mode switching DC-DC controller
supports boost or SEPIC topologies and operates in an
adjustable frequency range between 200kHz and 2MHz.
An integrated spread-spectrum mode helps reduce EMI.
Current-mode control with programmable slope compensation provides fast response and simplifies loop compensation. An adaptive output-voltage control scheme minimizes power dissipation in the LED current-sink paths.
The device has a separate p-channel drive (PGATE) pin
that is used for output undervoltage protection. Whenever
the output falls below the threshold, the external
p-MOSFET is latched off, disconnecting the input source.
Cycling the EN or the input supply is required to restart
the converter. The external p-MOSFET is off when the EN
pin is below 0.3V (typ). The shutdown current is 1µA (typ)
at an input voltage of 12V.
The device consists of four identical linear current-sink
channels, adjustable from 20mA to 150mA with an
accuracy of ±3% using a single external resistor. Multiple
channels can be connected in parallel to achieve higher
current per LED string. The device also features a unique
pulsed dimming control through a logic input (DIM),
with minimum pulse width as low as 500ns. Protection
features include output overvoltage, open-LED detection
and protection, programmable shorted-LED detection and
protection, output undervoltage detection and protection,
and overtemperature protection. The device operates
over the -40°C to +125°C automotive temperature range.
The MAX16813B is available in 20-pin (6.5mm x 4.4mm)
TSSOP and 20-pin (4mm x 4mm) TQFN packages.
19-100144; Rev 1; 1/18
Benefits and Features
●● 4-Channel Linear LED Current Sinks with Internal
MOSFETs Independently Drive Multiple LED Strings
• Full-Scale LED Current, Adjustable from 20mA
to 150mA
• Drives 1 to 4 LED Strings
• 10000:1 PWM Dimming at 200Hz
●● Flexible Current-Mode Architecture Supports a Wide
Range of Applications While Minimizing Interference
• Boost or SEPIC Current-Mode DC-DC Controller
• 200kHz to 2MHz Programmable Switching
Frequency
• External Switching-Frequency Synchronization
• Spread-Spectrum Mode
●● Protection Features Enhance Fault Detection and
System Reliability
• Output-to-Ground Undervoltage Protection
• Open-Drain Fault-Indicator Output
• Open-LED and LED-Short Detection and
Protection
• Overtemperature Protection
●● Adaptive Output-Voltage Optimization to Minimize
Power Dissipation
• Less than 2µA Shutdown Current
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
Ordering Information appears at end of data sheet.
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Absolute Maximum Ratings
OUT_ Continuous Current..............................................±175mA
VCC Short-Circuit Duration.........................................Continuous
Continuous Power Dissipation (TA = +70°C) (Note 1)
20-Pin TQFN (derate 25.6mW/°C above +70°C).......2051mW
20-Pin TSSOP (derate 26.5mW/°C above +70°C).....2122mW
Operating Temperature Range.......................... -40°C to +125°C
Junction Temperature.......................................................+150°C
Storage Temperature Range............................. -65°C to +150°C
Lead Temperature (soldering, 10s).................................. +300°C
Soldering Temperature (reflow)........................................+260°C
IN to SGND............................................................-0.3V to +45V
EN, PGATE to SGND....................................-0.3V to (IN + 0.3V)
PGND to SGND.....................................................-0.3V to +0.3V
LEDGND to SGND................................................-0.3V to +0.3V
OUT_ to LEDGND..................................................-0.3V to +45V
VCC to SGND............. -0.3V to the lower of (IN + 0.3V) and +6V
FLT, DIM, RSDT, OVP to SGND..............................-0.3V to +6V
CS, NDRV, RT, COMP, SETI to SGND..... -0.3V to (VCC + 0.3V)
NDRV Peak Current (< 100ns)..............................................±3A
NDRV Continuous Current..............................................±100mA
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)
TQFN
Junction-to-Ambient Thermal Resistance (θJA).........+39°C/W
Junction-to-Case Thermal Resistance (θJC)................+6°C/W
TSSOP
Junction-to-Ambient Thermal Resistance (θJA)......+37.7°C/W
Junction-to-Case Thermal Resistance (θJC).............+2.0°C/W
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 www.maximintegrated.com/thermal-tutorial.
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
PACKAGE TYPE
PACKAGE CODE
OUTLINE NO.
LAND PATTERN NO.
20 TSSOP-EP
U20E+6
21-0108
90-0114
20 TQFN-EP
T2044+3
21-0139
90-0037
Electrical Characteristics
(VIN = VEN = 12V, RRT = 12.25kΩ, RSETI = 15kΩ, CVCC = 1µF, NDRV = COMP = OUT_ = PGATE = unconnected, VRSDT = VDIM =
VCC, VOVP = 0.7V, VCS = VLEDGND = VPGND = VSGND = 0V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are
at TA = +25°C.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
40
V
3.4
5.7
mA
1
2
µA
4.3
4.625
SUPPLIES
Operating Voltage Range
VIN
Supply Current
IIN
Standby Supply Current
IN Undervoltage Lockout
IN UVLO Hysteresis
www.maximintegrated.com
IIN_Shdn
4.75
VOVP = 1.266V, all channels on,
VOUT_ = 0.5V
VEN = 0V
VIN rising
3.975
170
V
mV
Maxim Integrated │ 2
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Electrical Characteristics (continued)
(VIN = VEN = 12V, RRT = 12.25kΩ, RSETI = 15kΩ, CVCC = 1µF, NDRV = COMP = OUT_ = PGATE = unconnected, VRSDT = VDIM =
VCC, VOVP = 0.7V, VCS = VLEDGND = VPGND = VSGND = 0V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are
at TA = +25°C.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
4.75
5
5.25
4.75
5
5.25
VIN - VCC, VIN = 4.75V, ILOAD = 50mA
200
500
VCC shorted to SGND
100
mA
4
V
125
mV
VCC REGULATOR
Regulator Output Voltage
VCC
Dropout Voltage
Short-Circuit Current Limit
VCC_ILIM
VCC Undervoltage-Lockout
Threshold
6.5V < VIN < 10V, 1mA < ILOAD < 50mA
10V < VIN < 40V, 1mA < ILOAD < 10mA
VCC rising
VCC UVLO Hysteresis
V
mV
RT OSCILLATOR
Switching Frequency Range
fSW
Maximum Duty Cycle
200
fSW = 200kHz to 600kHz
90
94.5
98.5
fSW = 600kHz to 2000kHz
86
90.5
95
fSW = 200kHz to 2000kHz, frequency dither
disabled
Oscillator Frequency Accuracy
Frequency Dither
Frequency dithering disabled
fDITH
Dither enabled, fSW = from 200kHz to
2000kHz
Sync Rising Threshold
Minimum Sync Frequency
2000
-7.5
-5
-7
kHz
%
+7.5
%
-9
%
4
V
1.1fSW
kHz
PWM COMPARATOR
PWM Comparator Leading-Edge
Blanking
PWM-to-NDRV Propagation
Delay
Including leading-edge blanking time
60
ns
90
ns
SLOPE COMPENSATION
Peak Slope Compensation
Current Ramp Magnitude
Current ramp added to the CS input
45
50
55
µA
Current-Limit Threshold
(Note 3)
396
416
437
mV
CS Limit Comparator to NDRV
Propagation Delay
10mV overdrive, excluding leading edge
blanking time
CURRENT-SENSE COMPARATOR
10
ns
1
V
ERROR AMPLIFIER
OUT_ Regulation Voltage
Transconductance
gM
VCOMP = 2V
340
600
880
No-Load Gain
(Note 4)
COMP Sink Current
VOUT_ = 2.25V, VCOMP = 2V
160
375
800
µA
COMP Source Current
VOUT_ = 0V, VCOMP = 1.0V
160
375
800
µA
www.maximintegrated.com
75
µS
dB
Maxim Integrated │ 3
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Electrical Characteristics (continued)
(VIN = VEN = 12V, RRT = 12.25kΩ, RSETI = 15kΩ, CVCC = 1µF, NDRV = COMP = OUT_ = PGATE = unconnected, VRSDT = VDIM =
VCC, VOVP = 0.7V, VCS = VLEDGND = VPGND = VSGND = 0V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are
at TA = +25°C.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MOSFET DRIVER
NDRV On-Resistance
ISINK = 100mA (nMOS)
0.9
Ω
ISOURCE = 50mA (pMOS)
1.1
Ω
Peak Sink Current
VNDRV = 5V
2
A
Peak Source Current
VNDRV = 0V
2
A
Rise Time
CLOAD = 1nF
6
ns
Fall Time
CLOAD = 1nF
6
ns
LED CURRENT SOURCE
OUT_ Current Sink Range
Channel-to-Channel Matching
OUT_ Current
IOUT_ = 100mA
150
mA
-2
+2
%
RSETI = 30kΩ, TA = +25°C
RSETI = 30kΩ, TA = -40°C to +125°C
48.25
RSETI = 15kΩ, TA = +25°C
RSETI = 15kΩ, TA = -40°C to +125°C
RSETI = 10kΩ, TA = +25°C
OUT_ Leakage Current
20
RSETI = 10kΩ, TA = -40°C to +125°C
VDIM = 0V, VOUT_ = 40V
50
51.75
47.50
50
52.50
97
100
103
96
100
104
145.50
150
154.50
144
150
156
-2
+2
mA
µA
LOGIC INPUTS and OUTPUTS
EN Input Logic-High
2.1
V
EN Input Logic-Low
0.4
EN Hysteresis
EN Input Current
260
V
mV
VEN = 12V
7.5
15
µA
VEN = 0.3V
100
200
nA
DIM Input Logic-High
2.1
V
DIM Input Logic-Low
0.8
DIM Hysteresis
250
DIM Input Current
VDIM = 5V
DIM to LED Turn-On Delay
DIM rising edge to 10% rise in IOUT_
DIM to LED Turn-Off Delay
IOUT_ Rise Time
-2
V
mV
+2
µA
150
ns
DIM falling edge to 10% fall in IOUT_
50
ns
10% to 90% IOUT_
200
ns
IOUT_ Fall Time
90% to 10% IOUT_
50
ns
FLT Output Low Voltage
FLT Output Leakage Current
VIN = 4.75V and ISINK = 5mA
VFLT = 5.5V
-1
LED Short-Detection Threshold
VRSDT = 2V
6.1
Short-Detection Comparator
Delay
www.maximintegrated.com
7
6.5
0.4
V
+1
µA
7.9
V
µs
Maxim Integrated │ 4
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Electrical Characteristics (continued)
(VIN = VEN = 12V, RRT = 12.25kΩ, RSETI = 15kΩ, CVCC = 1µF, NDRV = COMP = OUT_ = PGATE = unconnected, VRSDT = VDIM =
VCC, VOVP = 0.7V, VCS = VLEDGND = VPGND = VSGND = 0V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are
at TA = +25°C.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
RSDT Leakage Current
VRSDT = 2.5V
-600
OVP Trip Threshold
OVP rising
1.190
OVP Hysteresis
TYP
MAX
UNITS
+600
nA
1.228
1.266
V
70
OVP Leakage Current
VOVP = 1.25V
-200
OVP Undervoltage-Detection
Threshold
OVP falling, PGATE latched off
0.485
OVP Undervoltage-Detection
Delay
OVP falling
5
Thermal-Shutdown Threshold
Temperature rising
Thermal-Shutdown Hysteresis
mV
+200
nA
0.585
0.685
V
10
20
µs
165
°C
15
°C
PGATE DRIVER
PGATE On-Resistance
PGATE Soft-Start Current
RPGATE
IPGATE = 10mA
Active during PGATE soft-start time
PGATE Soft-Start Time
PGATE Leakage Current
210
6.35
VPGATE = 12V, VEN = 0V
100
250
Ω
350
490
µA
10
13.25
ms
0.01
1
µA
Note 2: 100% tested at TA = +25°C. All limits over temperature are guaranteed by design, not production tested.
Note 3: CS threshold includes slope compensation ramp magnitude.
Note 4: Gain = dVCOMP/dVCS, 0.05V < VCS < 0.15V.
www.maximintegrated.com
Maxim Integrated │ 5
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Typical Operating Characteristics
(VIN = VEN = 12V, RRT = 21kΩ, RSETI = 15kΩ, CVCC = 1µF, NDRV = COMP = OUT_ = PGATE = unconnected, VOVP = 0.7V,
VCS = VLEDGND = VDIM = VPGND = VSGND = 0V, load = 4 strings of 7 white LEDs, TA = +25°C, unless otherwise noted.)
4.0
TA = -40°C
20
25
VIN (V)
30
35
VCC LOAD REGULATION
EN THRESHOLD VOLTAGE (V)
TA = +125°C
5.00
4.98
TA = +25°C
4.96
4.94
TA = -40°C
40
60
80
1.4
1.3
1.2
1.1
VEN FALLING
1.0
-50
IOUT(AVG) vs. 1/RSETI
160
-25
100
IOUT(AVG) = (IOUT1 + IOUT2 +
IOUT3 + IOUT4)/4
140
IOUT(AVG) (mA)
100
80
60
-0.4
40
-50
-25
0
25
50
75
TEMPERATURE (°C)
www.maximintegrated.com
100
125
20
toc03
10.0
25
30
35
40
100
125
9.0
8.5
8.0
7.5
7.0
10
25
40
55
1/RSETI (mS)
6.0
125
120
-0.3
20
6.5
VSETI ERROR vs. TEMPERATURE
-0.2
15
9.5
VEN RISING
IVCC (mA)
-0.1
10
EN INPUT CURRENT
vs. TEMPERATURE
0
25
50
75
TEMPERATURE (°C)
0
5
EN THRESHOLD VOLTAGE
vs. TEMPERATURE
1.5
0.8
100
TA = -40°C
VIN (V)
0.9
toc07
0.1
20
TA = +25°C
fSW (kHz)
70
85
100
-50
-25
0
25
50
75
TEMPERATURE (°C)
OUT_ LEAKAGE CURRENT
vs. TEMPERATURE
100
OUT_ LEAKAGE CURRENT (nA)
0
5.00
4.97
200 400 600 800 1000 1200 1400 1600 1800 2000
1.6
toc04
5.02
VCC (V)
3.6
40
EN INPUT CURRENT (µA)
15
toc05
10
TA = +125°C
4.98
toc08
5
5.01
4.99
3.8
3.6
VSETI ERROR (%)
4.2
4.0
3.8
-0.5
4.4
VCC (V)
TA = +25°C
4.2
4.92
5.02
4.6
4.4
IIN (mA)
IIN (mA)
4.6
3.4
CNDRV = 13pF
4.8
toc06
TA = +125°C
VCC LINE REGULATION
5.03
toc09
CNDRV = 13pF
4.8
5.0
toc01
5.0
SUPPLY CURRENT
vs. SWITCHING FREQUENCY
toc02
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
VDIM = 0V
VOUT_ = 40V
10
1
0.1
0.01
-50
-25
0
25
50
75
100
125
TEMPERATURE (°C)
Maxim Integrated │ 6
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Typical Operating Characteristics (continued)
(VIN = VEN = 12V, RRT = 21kΩ, RSETI = 15kΩ, CVCC = 1µF, NDRV = COMP = OUT_ = PGATE = unconnected, VOVP = 0.7V,
VCS = VLEDGND = VDIM = VPGND = VSGND = 0V, load = 4 strings of 7 white LEDs, TA = +25°C, unless otherwise noted.)
RSDT LEAKAGE CURRENT (nA)
1.8
toc12
1.6
1.4
1.2
1.0
0.8
0.6
0.4
toc11
VOVP = 0.7V
SWITCHING WAVEFORM AT 5kHz
(50% DUTY CYCLE) DIMMING
300
toc10
2.0
OVP LEAKAGE CURRENT (nA)
RSDT LEAKAGE CURRENT
vs. TEMPERATURE
OVP LEAKAGE CURRENT
vs. TEMPERATURE
VLX
10V/div
250
200
0V
VRSDT = 2.5V
IOUT_
100mA/div
150
0A
VBOOST
10V/div
100
0.2
0
-50
-25
0
25
50
75
100
50
125
-50
-25
0
25
50
75
100
125
0V
40µs/div
TEMPERATURE (°C)
TEMPERATURE (°C)
LED CURRENT WAVEFORM WITH
DIM ON PULSE WIDTH OF 25µs
LED CURRENT WAVEFORM WITH
DIM ON PULSE WIDTH OF 1µs
toc13
toc14
VDIM
5V/div
0V
VDIM
5V/div
0V
IOUT_
50mA/div
IOUT_
50mA/div
0A
0A
4µs/div
200ns/div
STARTUP WAVEFORM WITH
DIM ON PULSE WIDTH < 24tSW
STARTUP WAVEFORM WITH
DIM ON PULSE WIDTH ≥ 24tSW
toc15
toc16
0V
VIN
20V/div
0V
0V
VDIM
5V/div
0V
VDIM
5V/div
0A
IOUT_
100mA/div
IOUT_
100mA/div
0A
VIN
20V/div
VBOOST
20V/div
0V
www.maximintegrated.com
20ms/div
VBOOST
10V/div
0V
20ms/div
Maxim Integrated │ 7
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Typical Operating Characteristics (continued)
(VIN = VEN = 12V, RRT = 21kΩ, RSETI = 15kΩ, CVCC = 1µF, NDRV = COMP = OUT_ = PGATE = unconnected, VOVP = 0.7V,
VCS = VLEDGND = VDIM = VPGND = VSGND = 0V, load = 4 strings of 7 white LEDs, TA = +25°C, unless otherwise noted.)
STARTUP WAVEFORM WITH
DIM CONTINUOUSLY ON
STARTUP WAVEFORM OF PGATE
AND INDUCTOR CURRENT WITH
DIM CONTINUOUSLY ON
toc17
toc18
VEN
2V/div
VIN
20V/div
0V
0V
0A
0V
VDIM
5V/div
0V
IOUT_
100mA/div
0V
VBOOST
10V/div
0V
0A
20ms/div
VBOOST
10V/div
VPGATE
10V/div
ILX
1A/div
20ms/div
STARTUP WAVEFORMS WITH
DELAYED DIM INPUT
OUTPUT UNDERVOLTAGE FAULT
toc19
0V
VPGATE
10V/div
0V
VFLT
5V/div
0V
VBOOST
10V/div
toc20
VIN
10V/div
0V
VDIM
5V/div
0V
VBOOST
20V/div
0V
VOVP
200mV/div
0A
0V
1ms/div
FUNCTIONALITY WITH DIM = 0
FOR DURATION > 38ms (TYP)
IBOOST
500mA/div
1s/div
DIM LOW DETECTION PERIOD
toc21
VIN
10V/div
0V
VDIM
5V/div
VDIM
5V/div
0V
VBOOST
10V/div
0V
38ms
VBOOST
20V/div
0V
0V
IBOOST
500mA/div
0A
www.maximintegrated.com
toc22
100ms/div
IBOOST
500mA/div
0A
10ms/div
Maxim Integrated │ 8
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
OUT3
LEDGND
OUT2
OUT1
TOP VIEW
OUT4
Pin Configuration
15
14
13
12
11
NDRV 1
CS 16
10
DIM
PGND 17
9
SGND
MAX16813B
NDRV 18
PGATE 19
EP*
3
4
5
RT
FLT
2
COMP
1
EN
+
IN
VCC 20
8
RSDT
7
SETI
6
OVP
+
20 PGND
19 CS
PGATE 2
VCC 3
IN 4
EN 5
18 OUT4
MAX16813B
17 OUT3
16 LEDGND
COMP 6
15 OUT2
RT 7
14 OUT1
FLT 8
13 DIM
OVP 9
12 SGND
SETI 10
EP*
11 RSDT
TSSOP
TQFN
*EXPOSED PAD.
Pin Description
PIN
NAME
FUNCTION
TQFN
TSSOP
1
4
IN
Bias Supply Input. Connect a 4.75V to 40V supply to IN. Bypass IN to SGND with a ceramic
capacitor.
2
5
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 input should not be left open.
3
6
COMP
Switching Converter Compensation Input. Connect the compensation network from COMP
to SGND for current-mode control (see the Feedback Compensation section).
4
7
RT
Oscillator Timing Resistor Connection. Connect a timing resistor (RT) from RT to SGND to
program the switching frequency according to the formula RT = 7.72 x 109/fSW. Apply an
AC-coupled external clock at RT to synchronize the switching frequency with an external clock.
When the oscillator is synchronized with the external clock, the spread spectrum is disabled.
5
8
FLT
Open-Drain Fault Output. FLT asserts low when an open LED, short LED, output undervoltage,
or thermal shutdown is detected. Connect a pullup resistor from FLT to VCC.
6
9
OVP
Overvoltage/Undervoltage-Threshold Adjust Input. Connect a resistor-divider from the switching
converter output to OVP and SGND. The OVP comparator reference is internally set to 1.23V.
7
10
SETI
LED Current-Adjust Input. Connect a resistor (RSETI) from SETI to SGND to set the current
through each LED string (ILED), according to the formula ILED = 1500/RSETI.
8
11
RSDT
LED Short Detection Threshold-Adjust Input. Connect a resistive divider from VCC to RSDT and
SGND to program the LED short detection threshold. Connect RSDT directly to VCC to disable
LED short detection.
www.maximintegrated.com
Maxim Integrated │ 9
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Pin Description (continued)
PIN
NAME
FUNCTION
TQFN
TSSOP
9
12
SGND
10
13
DIM
Digital PWM Dimming Input. Apply a PWM signal to DIM for LED dimming control. Connect DIM
to VCC if dimming control is not used.
11
14
OUT1
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.
12
15
OUT2
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.
13
16
LEDGND
14
17
OUT3
LED String Cathode Connection 3. OUT3 is the open-drain output of the linear current sink that
controls the current through the LED string connected to OUT3. OUT3 sinks up to 150mA. If
unused, connect OUT3 to LEDGND.
15
18
OUT4
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.
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).
Signal Ground. SGND is the current return path connection for the low-noise analog signals.
Connect SGND, LEDGND, and PGND at a single point.
LED Ground. LEDGND is the return path connection for the linear current sinks. Connect
SGND, LEDGND, and PGND at a single point.
16
19
CS
17
20
PGND
Power Ground. PGND is the switching current return path connection. Connect SGND,
LEDGND, and PGND at a single point.
18
1
NDRV
Switching n-MOSFET Gate-Driver Output. Connect NDRV to the gate of the external switching
power MOSFET.
19
2
PGATE
External p-MOSFET Gate connection. Connect a resistor from this pin to the external
p-MOSFET gate. Connect PGATE to PGND through a resistor (0 to 10kΩ) if not used.
20
3
VCC
5V Regulator Output. Bypass VCC to SGND with a minimum of 1µF ceramic capacitor as close
as possible to the device.
—
—
EP
Exposed Pad. Connect EP to a large-area contiguous copper ground plane for effective power
dissipation. Do not use EP as the main IC ground connection. EP must be connected to SGND.
www.maximintegrated.com
Maxim Integrated │ 10
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
RSDT
(SHORTED-LED THRESHOLD)
FLT
PWROND
MAX16813B
FAULT FLAG
LOGIC
VCC
SHDN
UNUSED–
STRING
DETECTOR
PWM
LOGIC
PGND
RT
OPEN-LED
DETECTOR
TSHDN
DRIVER
NDRV
SHORT-LED
DETECTOR
UV
CLK
OUT1–
OUT4
MINIMUM
STRING
VOLTAGE
PWM
PWM
COMP
COMP
RT OSCILLATOR /RAMP
FOR SLOPE
COMPENSATION
COMP
$ARRAY = 4
DRIVER
PGATE
PGATE
SOFT–START
POK
gM
PWRON
ILIM
IN
0 1
UVLO
R
LOGIC
0.425V
SHDN
VCC
5V LDO
0 1
BANDGAP
CLK
MINSTR
MINSTR
_REF
THERMAL
SHUTDOWN
POK
UVLO
LODIMB
MINIMUM CYCLES
BLOCK
OVP
COMPARATOR
TSHDN
LEDGND
0 1
DIM
IN
EN
INPUT
BUFFER
PWROND TSHDN
CS
RAMP FROM
RT OSCILLATOR
POK
PWRON
0.95*VBG
SHDN
SSDONE
CS BLANKING
SLOPE
COMPENSATION
INTERNAL
DPWM
UV
DETECTION
BLOCK
0.585V
0.185V
SS
SHDN
SS_REF
SOFT-START
100ms
VCC
VBG
SS
PWROND
SD_MIN
TSHDN
SGND
OVP
SETI
Figure 1. Simplified Functional Diagram
www.maximintegrated.com
Maxim Integrated │ 11
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Q2
L1
22µH
VIN
C1
1µF
D3
R10
15kΩ
C7
0.047µF
D1
D2
R1
261kΩ
Q1
C2
22µF
8 LEDs
PER
STRING
RCS
0.15Ω
R2
10kΩ
RSCOMP
3.32kΩ
R7
1.4kΩ
NDRV
CS
OVP
PGATE
ENABLE INPUT
OUT1
EN
OUT2
OUT3
IN
C3
1µF
VCC
MAX16813B
OUT4
SETI
RSETI
18.2kΩ
R6
10kΩ
DIM
FLT
COMP
RCOMP
825Ω
R3
30.1kΩ
RSDT
CCOMP
2.2µF
VCC
RT
SGND
PGND
LEDGND
RT
18.7Ω
R4
20kΩ
Figure 2. Typical Operating Circuit
Detailed Description
The MAX16813B 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 device incorporates two major blocks: a DC-DC
controller with peak-current-mode control to implement a
boost or a SEPIC-type switched-mode power supply and
a 4-channel LED driver with 20mA to 150mA constantcurrent sink capability per channel. Figure 1 is the
simplified functional diagram and Figure 2 shows a
typical operating circuit.
www.maximintegrated.com
The device features a constant-frequency peak currentmode control with programmable slope compensation to
control the duty cycle of the PWM controller. The highcurrent FET driver can provide up to 2A of current to the
external n-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 4 LED strings.
The device features adaptive voltage control that adjusts
the converter output voltage depending on the forward
Maxim Integrated │ 12
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
voltage of the LED strings. This feature minimizes the
voltage drop across the constant-current sink drivers
and reduces power dissipation in the device. The device
includes an internal 5V LDO capable of powering additional external circuitry. A logic input (EN) shuts down the
device when pulled low. When the EN pin is pulled below
0.3V (typ), the quiescent input current to the device is less
than 1µA (typ).
The device provides a very wide (10000:1) PWM
dimming range where a dimming pulse as narrow as
500ns 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 condition.
Shorted-LED string-detection and overvoltage-protection
thresholds are programmable using the RSDT and OVP
inputs, respectively. An open-drain FLT signal asserts
to indicate open-LED, shorted-LED, output undervoltage and overtemperature 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 exceeds +165°C.
There are two levels of output undervoltage protection in
the device. The first output undervoltage protection is set
at 180mV and this is enabled 43ms after power-up. If the
OVP pin is lower than 180mV after 43ms, it turns off the
converter and disconnects the p-MOSFET from the input.
The second undervoltage threshold is activated after the
soft-start period of the DC-DC converter. This is set at
585mV. If the OVP pin is below 585mV after the soft-start
period of the DC-DC converter, the converter is turned off
and the p-MOSFET disconnects the input voltage from
the LED driver. See the Startup Sequence section for
more details.
www.maximintegrated.com
Current-Mode DC-DC Controller
The peak current-mode controller allows boost or SEPICtype converters to generate 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 50% duty cycles
in continuous-conduction mode.
The external n-MOSFET is turned on at the beginning
of every switching cycle. The inductor current ramps up
linearly until 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 (RCS)
connected from the source of the external n-MOSFET
to PGND. The device features leading-edge blanking
to suppress the external n-MOSFET switching noise.
A PWM comparator compares the current-sense voltage plus the slope-compensation signal with the output
of the transconductance error amplifier. The controller
turns off the external n-MOSFET when the voltage at
CS exceeds the error amplifier’s output voltage. This
process repeats every switching cycle to achieve peakcurrent-mode control.
Error Amplifier
The internal error amplifier compares an internal feedback
(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 four constantcurrent 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.
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
compensation capacitor charge. This allows the converter
to settle to a 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.
Maxim Integrated │ 13
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
If the PWM dimming on-pulse is less than or equal to 24
switching cycles, the feedback controls the voltage on
OVP so that the converter output voltage is regulated at
95% 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.
Input and VCC Undervoltage Lockout (UVLO)
recycled. If there is no undervoltage, soft-start terminates
when the minimum current sink voltage reaches 1V (typ)
or when an internal 100ms timeout expires.
After soft-start, the device detects open LED and disconnects any strings with an open LED from the internal
minimum OUT_ voltage detector. The converter output
discharges to a level where the new minimum OUT_
voltage is 1V and then control is handed over to the
internal minimum OUT_ voltage detector.
The device features two undervoltage lockouts that monitor
the input voltage at IN and the output of the internal LDO
regulator at VCC. The device turns on after both IN and
VCC exceed their respective UVLO thresholds. The UVLO
threshold at IN is 4.3V when IN is rising and 4.13V when
IN is falling. The UVLO threshold at VCC is 4V when VCC
is rising and 3.875V when VCC is falling.
A second output undervoltage protection is enabled
100ms after the converter is enabled. A fault is detected
whenever the OVP pin falls below an internal threshold
of 585mV (typ) and the power converter is latched off
and PGATE goes high. Cycling the EN pin or the supply
is required to start up again, once the fault condition has
been removed.
Enable
Oscillator Frequency/External
Synchronization
The device is enabled using the EN logic input pin. The
EN input can handle voltages up to IN, providing flexibility in terms of control signals/supplies. To shut down the
device, drive the EN pin with a logic-low, which reduces
current consumption to 1µA (typ). Connect the EN pin to
IN if not used. EN should not be left open.
The internal oscillator frequency is programmable between
200kHz and 2MHz using a timing resistor (RT) connected
from the RT input to SGND. Use the equation below
to calculate the value of RT for the desired switching
frequency (fSW):
Startup Sequence
Once EN is driven high, the controller remains off until
both IN and VCC trip their rising thresholds.
Once UVLO conditions are satisfied, the driver of the
external p-MOSFET is turned on. A constant current
of 350µA (typ) flows into the PGATE pin of the device
for approximately 10ms (typ). The current flowing into
resistor R7 and capacitor C7 (see Figure 2) pulls down
the gate of the external p-MOSFET. This capacitor
controls the turn-on time of the external p-MOSFET.
After the external p-MOSFET Q2 (Figure 2) is turned
on and the 10ms timeout expires, the device detects
and then disconnects any unused current sink
channels before enabling the converter. Disable the
unused current sink channels by connecting the
corresponding OUT_ to LEDGND. This avoids asserting
the FLT output for the unused channels. The detection of
unused channels takes approximately 0.7ms (typ).
Once the above phase is completed, the DC-DC converter
is enabled and the soft-start is initiated. During soft-start,
the DC-DC converter output ramps up as the loop regulates the voltage at the OVP pin to follow an internal ramping voltage. 33ms (typ) after the converter is enabled, the
OVP pin is monitored, and if the voltage at the OVP pin
is less than 180mV (typ), FLT is asserted low, the power
converter is turned off, the external p-MOSFET is turned
off, and they all stay off until the EN pin or the supply is
www.maximintegrated.com
RT =
7.72 × 10 9
f SW
where fSW is in Hz.
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:
9.862
C SYNC ≤
− 0.144 × 10 -3 (µF)
RT
where RT is in ohms.
The pulse width for the synchronization pulse should satisfy the following relations:
t PW
VS < 0.5
t CLK
t PW
VS + VS > 3.4
0.8 −
t CLK
t CLK
t PW <
(t CI − 1.05 × t CLK )
t CI
where tPW is the synchronization source pulse width,
tCLK is the synchronization clock time period, tCI is the
programmed clock period, and VS is the synchronization
pulse voltage level.
Maxim Integrated │ 14
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Spread-Spectrum Mode
The device includes a unique spread-spectrum mode
(SSM) that reduces emission (EMI) at the switching
frequency and its harmonics.
The spread spectrum uses a pseudorandom dithering
technique where the switching frequency is varied in the
range of 93% of the programmed switching frequency, to
100% of the programmed switching frequency set through
the external resistor from RT to SGND.
Instead of a large amount of spectral energy present at
multiples of the switching frequency, the total energy at
the fundamental and each harmonic is spread over a
wider bandwidth, reducing the energy peak.
Spread spectrum is only disabled if external synchronization is used.
5V LDO Regulator (VCC)
The internal LDO regulator converts the input voltage
at IN to a 5V output voltage at VCC. The LDO regulator
supplies up to 50mA current to provide power to internal
control circuitry and the gate driver. Bypass VCC to SGND
with a minimum of 1µF ceramic capacitor as close as
possible to the device.
PWM MOSFET Driver
The NDRV output is a push-pull output with the
on-resistance of the p-MOSFET (typically 1.1Ω) and
the on-resistance of the n-MOSFET (typically 0.9Ω).
NDRV swings from PGND to VCC to drive an external
n-MOSFET. The driver typically sources 2.0A and sinks
2.0A allowing for fast turn-on and turn-off of high gatecharge MOSFETs.
The power dissipation in the device is mainly a function
of the average current sourced to drive the external
MOSFET (IVCC) if there are no additional loads on
VCC. IVCC depends on the total gate charge (QG) and
operating frequency of the converter.
LED string, use two or more of the current source outputs
(OUT_) connected together to drive the string, as shown
in Figure 3.
LED Dimming Control
The device features LED brightness control using an
external PWM signal applied to DIM. A logic-high signal
on the DIM input enables all four LED current sources and
a logic-low signal disables them.
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 24 oscillator clock cycles (DIM pulse width increasing), the boost
converter regulates its output based on feedback from
the OVP input. While in this mode, the converter output
voltage is regulated to 95% of the overvoltage threshold
at the OVP pin. If the turn-on duration of the PWM signal
is greater than or equal to 24 oscillator clock cycles (DIM
pulse width increasing), the converter regulates its output
so that the minimum voltage at OUT_ is 1V.
At power-up, if the converter has completed the soft-start
period of 100ms (typ) and the PWM signal at the DIM pin
is still low, the device regulates the output voltage based
on the feedback signal coming from the OVP pin. Once a
PWM pulse width greater than 24 oscillator clock cycles
is applied, the converter regulates its output so that the
minimum voltage at OUT_ is 1V.
The converter output voltage is regulated to 95% of the
overvoltage threshold at the OVP pin whenever the PWM
signal at the DIM pin is forced low for a duration longer
than 38ms (typ).
BOOST CONVERTER
OUTPUT
40mA TO 300mA
PER STRING
LED Current Control
The device features four identical constant-current sources
used to drive multiple HB LED strings. The current through
each one of the four channels is adjustable between
20mA and 150mA using an external resistor (RSETI)
connected between SETI and SGND. Select RSETI using
the following formula:
RSETI = 1500/IOUT_
where IOUT_ is the desired output current for each of
the four channels. If more than 150mA is required in an
www.maximintegrated.com
OUT1
MAX16813B
OUT2
OUT3
OUT4
Figure 3. Configuration for Higher LED String Current
Maxim Integrated │ 15
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Fault Protections
Fault protections in the device include cycle-by-cycle
current limiting using the PWM controller, DC-DC
converter output overvoltage protection, open-LED detection, short-LED detection and protection, output undervoltage protection, and overtemperature shutdown. An
open-drain fault flag output (FLT) goes low when an openLED string is detected, a shorted-LED string is detected,
an output undervoltage, or 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 or output undervoltage condition, and
can be reset by cycling power or toggling the EN pin. The
thermal-shutdown threshold is +165°C and has +15°C
hysteresis.
Open-LED Management and
Overvoltage Protection
On power-up, the device detects and disconnects any
unused current sink channels before entering the DC-DC
converter 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 device detects
open LED and disconnects any strings with an open
LED from the internal minimum OUT_ voltage detector.
This keeps the DC-DC converter output voltage within
safe limits and maintains high efficiency. 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 VLEDGND. The DC-DC converter output
voltage then increases to the overvoltage-protection
threshold set by the voltage-divider network connected
between the converter output, OVP input, and SGND. The
overvoltage-protection threshold at the DC-DC converter
output (VOVP) is determined using the following formula:
R1
VOVP= 1.23 × 1 +
(see Figure 2)
R2
where 1.23V (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
converter output reaches the overvoltage-protection
threshold, the PWM controller is switched off setting
NDRV low. Any current sink output with VOUT_ < 300mV
(typ) is disconnected from the minimum voltage detector.
www.maximintegrated.com
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. Open-LED detection
is disabled when PWM dimming pulse width is less than
24 switching clock cycles.
Short-LED Detection
The device checks for shorted LEDs at each rising edge
of DIM. An LED short is detected at OUT_ if the following
condition is met:
VOUT_ > VMINSTR + 3 x VRSDT
where VOUT_ is the voltage at OUT_, VMINSTR is
the minimum current sink voltage, and VRSDT is the
programmable-LED short-detection threshold set at the
RSDT input (with VRSDT less than or equal to 2.5V).
Adjust VRSDT to a voltage less than or equal to 2.5V
using a voltage-divider resistive network connected at
the VCC output, RSDT input, and SGND. 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 VCC to always disable LED short detection.
Short-LED detection is disabled when PWM dimming
pulse width is less than 24 switching clock cycles.
Applications Information
DC-DC Converter
Three different converter topologies are possible
with the DC-DC controller in the device, 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 buck-boost converter
topology. Buck-boost topology is implemented using
either a conventional SEPIC configuration or a
coupled-inductor buck-boost configuration. The latter is
basically a flyback converter with 1:1 turns ratio. 1:1coupled inductors are available with tight coupling
suitable for this application. Figure 4 shows the coupled-inductor buck-boost configuration. It is also possible to implement a single inductor converter using the
MAX15054 high-side FET driver.
Maxim Integrated │ 16
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
The boost converter topology provides the highest efficiency among the above-mentioned topologies. The
coupled-inductor topology has the advantage of not using
a coupling capacitor over the SEPIC configuration. Also,
the feedback loop compensation for SEPIC becomes
complex if the coupling capacitor is not large enough.
range, the maximum voltage needed to drive the LED
strings including the minimum 1V across the constant
LED current sink (VLED), and the total output current
needed to drive the LED strings (ILED) as follows:
ILED = ISRTING x NSRTING
where ISRTING is the LED current per string in amperes
and NSRTING is the number of strings used.
Power-Circuit Design
First select a converter topology based on the above
factors. Determine the required input supply voltage
VIN
4.75V TO 40V
T1
(1:1)
D1
C1
UP TO 40V
R1
N
RCS
RSCOMP
IN
C3
NDRV
CS
C2
R2
OVP
EN
OUT1
VCC
OUT2
MAX16813B
PGATE
OUT3
OUT4
RSETI
SETI
DIM
FLT
COMP
R3
VCC
RSDT
RCOMP
CCOMP
RT
SGND
PGND
LEDGND
R4
RT
Figure 4. Coupled-Inductor Buck-Boost Configuration
www.maximintegrated.com
Maxim Integrated │ 17
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Calculate the maximum duty cycle (DMAX) using the
following equations:
For boost configuration:
(VLED + VD1 − VIN_MIN )
D MAX =
(VLED + VD1 − VDS − 0.3V)
For SEPIC and coupled-inductor buck-boost configurations:
(VLED + VD1)
D MAX =
(VIN_MIN − VDS − 0.3V + VLED + VD1)
where VD1 is the forward drop of the rectifier diode in
volts (approximately 0.6V), VIN_MIN is the minimum input
supply voltage in volts, and VDS is the drain-to-source
voltage of the external MOSFET in volts when it is on,
and 0.3V is the peak current-sense voltage. Initially, use
an approximate value of 0.2V for VDS to calculate DMAX.
Calculate a more accurate value of DMAX after the power
MOSFET is selected based on the maximum inductor
current. Select the switching frequency (fSW) depending
on the space, noise, and efficiency constraints.
Boost and Coupled-Inductor Configurations
In all three converter configurations, the average
inductor current varies with the input line voltage and the
maximum average current occurs at the lowest input 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 (ΔIL). The
recommended peak-to-peak ripple is 60% of the average
inductor current.
Use the following equations to calculate the maximum
average inductor current (ILAVG) and peak inductor
current (ILP) in amperes:
IL AVG =
ILED
1 − D MAX
Allowing the peak-to-peak inductor ripple ∆IL to be ±30%
of the average inductor current:
and
∆IL = ILAVG x 0.3 x 2
∆IL
=
IL P IL AVG +
2
Calculate the minimum inductance value (LMIN) in henries
with the inductor current ripple set to the maximum value:
(VIN_MIN − VDS − 0.3V) × D MAX
L MIN =
f SW × ∆IL
where 0.3V is the peak current-sense voltage. Choose
an inductor that has a minimum inductance greater
than the calculated LMIN and current rating greater than
www.maximintegrated.com
ILP. The recommended saturation current limit of the
selected inductor is 10% higher than the inductor peak
current for boost configuration. For the coupled inductor,
the saturation limit of the inductor with only one winding
conducting should be 10% higher than ILP.
SEPIC Configuration
Power-circuit design for the SEPIC configuration is very
similar to a conventional design with the output voltage
referenced to the input supply voltage. For SEPIC, the
output is referenced to ground and the inductor is split into
two parts (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.
Use the following equations to calculate the average
inductor currents (IL1AVG, IL2AVG) and peak inductor
currents (IL1P, IL2P) in amperes:
I
× D MAX × 1.1
IL1AVG = LED
1 − D MAX
The factor 1.1 provides a 10% margin to account for the
converter losses:
IL2AVG = ILED
Assuming the peak-to-peak inductor ripple ∆IL is ±30% of
the average inductor current:
∆IL1 = IL1AVG x 0.3 x 2
and:
=
IL1P IL1AVG +
∆IL1
2
∆IL2 = IL2AVG x 0.3 x 2
and:
IL2 P IL2 AVG +
=
∆IL2
2
Calculate the minimum inductance values L1MIN and
L2MIN in henries with the inductor current ripples set to
the maximum value as follows:
L1MIN =
L2 MIN =
(VIN_MIN − VDS − 0.3V) × D MAX
f SW × ∆IL1
(VIN_MIN − VDS − 0.3V) × D MAX
f SW × ∆IL2
where 0.3V is the peak current-sense voltage. Choose
inductors that have a minimum inductance greater than
the calculated L1MIN and L2MIN and current rating greater
than IL1P and IL2P, respectively. The recommended
saturation current limit of the selected inductor is 10%
higher than the inductor peak current.
Maxim Integrated │ 18
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
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:
L MIN =
and:
Select coupling capacitor CS so that the peak-to-peak
ripple on it is less than 2% of the minimum input supply
voltage. This ensures that the second-order effects created
by the series resonant circuit comprising L1, CS, and L2 do
not affect the normal operation of the converter. Use the
following equation to calculate the minimum value of CS:
L1MIN × L2 MIN
L1MIN + L2 MIN
CS ≥
ILAVG = IL1AVG + IL2AVG
where CS is the minimum value of the coupling capacitor
in farads, ILED is the LED current in amperes, and the
factor 0.02 accounts for 2% ripple.
where ILAVG represents the total average current through
both the inductors together for SEPIC configuration. Use
these values in the calculations for SEPIC configuration
in the following sections.
C4
L1
VIN
ILED × D MAX
VIN_MIN × 0.02 × f SW
D1
C1
C2
R1
L2
Q1
RCS
R2
RSCOMP
NDRV
CS
OVP
PGATE
ENABLE
INPUT
OUT1
OUT2
EN
OUT3
IN
MAX16813B
OUT4
SETI
VCC
C3
RSETI
VCC
R6
FLT
DIM
R3
RSDT
COMP
RT
RCOMP
CCOMP
SGND
PGND
LEDGND
RT
R4
Figure 5. SEPIC LED Driver
www.maximintegrated.com
Maxim Integrated │ 19
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Slope Compensation
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 is usually
minimized. In this case, an additional electrolytic or tantalum capacitor provides most of the bulk capacitance.
Use the following equation to calculate the value of slope
compensation resistance (RSCOMP):
External Switching-MOSFET Selection
The device generates a current ramp for slope
compensation. This ramp current is in sync with the
switching frequency and starts from zero at the beginning
of every clock cycle and rises linearly to reach 50µA
at the end of the clock cycle. The slope-compensating
resistor, (RSCOMP), is connected between the CS input
and the source of the external MOSFET. This adds a
programmable ramp voltage to the CS input voltage to
provide slope compensation.
For boost configuration:
R SCOMP =
(VLED − 2VIN_MIN ) × R CS × 3
L MIN × 50µA × f SW × 4
For SEPIC and coupled inductor:
R SCOMP =
( VLED
− VIN_MIN
) × R CS × 3
L MIN × 50µA × f SW × 4
where VLED and VIN_MIN are in volts, RSCOMP and RCS
are in ohms, LMIN is in henries, and fSW is in hertz. The
value of the switch current-sense resistor, (RCS) can be
calculated as follows:
For boost:
0.396 × 0.9 = ILP × RCS +
For SEPIC:
0.396 × 0.9 = ILP × RCS +
(D MAX × (VLED − 2VIN_MIN )× RCS × 3)
4 × L MN × f SW
(D MAX × (VLED − VIN_MIN ) × R CS × 3)
The external switching MOSFET should have a voltage
rating sufficient to withstand the maximum output voltage
together with the rectifier diode drop and any possible
overshoot due to ringing caused by parasitic inductances
and capacitances. The recommended MOSFET VDS
voltage rating is 30% higher than the sum of the maximum
output voltage and the rectifier diode drop.
The recommended continuous-drain current rating of the
MOSFET (ID), when the case temperature is at +70°C, is
greater than that calculated below:
ID RMS= IL AVG 2 × D MAX × 1.3
The MOSFET dissipates power due to both switching
losses and conduction losses. Use the following equation
to calculate the conduction losses in the MOSFET:
PCOND = ILAVG2 x DMAX x RDS(ON)
where RDS(ON) is the on-state drain-to-source resistance
of the MOSFET. Use the following equation to calculate
the switching losses in the MOSFET:
4 × L MN × f SW
IL AVG × VLED 2 × C GD × f SW 1
1
=
×
+
PSW
2
where 0.396 is the minimum value of the peak current I GON I GOFF
sense threshold. The current-sense threshold also
where IGON and IGOFF are the gate currents of the
includes the slope-compensation component. The
MOSFET in amperes when it is turned on and turned
minimum current-sense threshold of 0.396 is multiplied
off, respectively. CGD is the gate-to-drain MOSFET
by 0.9 to take tolerances into account.
capacitance in farads.
Output Capacitor Selection
For all three converter topologies, the output capacitor supplies the load current when the main switch is
on. The function of the output capacitor is to reduce the
converter output ripple to acceptable levels. The entire
output-voltage ripple appears across constant-current sink
outputs because the LED string voltages are stable due to
the constant current. For the device, limit the peak-to-peak
output-voltage ripple to 200mV to get stable output current.
Rectifier Diode Selection
Using a Schottky rectifier diode produces less forward drop
and puts the least burden on the MOSFET during reverse
recovery. A diode with considerable reverse-recovery time
increases the MOSFET switching loss. Select a Schottky
diode with a voltage rating 20% higher than the maximum
boost-converter output voltage and current rating greater
than that calculated in the following equation:
ID = IL AVG (1 − D MAX ) × 1.2
www.maximintegrated.com
Maxim Integrated │ 20
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Setting RSDT Pin Voltage
relationship between the RSDT voltage and the recommended maximum OUT_ voltage, assuming all the active
channels are at the same voltage level.
As described in the Short-LED Detection section, the
actual LED short detection threshold depends on the
RSDT pin voltage and the minimum current sink (OUT_)
voltage.
With higher OUT_ voltages, an erroneous LED short
condition can sometimes be detected when the converter
output voltage is transitioning from regulation based on
the OVP input to regulation based on the OUT_ voltages.
An optimum choice of RSDT voltage should take into
account the maximum voltage at the OUT_ pins when
the converter is regulating its output voltage based on the
OVP pin.
The plot shown here can be used when selecting the OVP
resistor divider and the RSDT voltage. It is recommended
that the RSDT voltage be chosen to be below the curve.
In general, performance is improved when the OVP resistor divider is selected to set a maximum output voltage
close to the maximum LED string voltage needed in the
application.
In particular, it is recommended that the OVP resistor
divider be selected to set the output voltage of the converter (when using the OVP input) so that the voltage on
the OUT_ pins does not exceed a threshold that depends
on the RSDT setting. The plot in Figure 6 shows the
MAXIMUM OUT_VOLTAGE vs. RSDT VOLTAGE
WITH VCC = 5V
ACTIVE OUT_ PINS AT THE SAME VOLTAGE LEVEL
45
40
35
OUT_ VOLTAGE (V)
30
25
NOT
RECOMMENDED
20
RECOMMENDED
15
10
5
0
0.3
0.5
0.7
0.9
1.1
1.3
1.5
1.7
1.9
2.1
2.3
2.5
VRSDT (V)
Figure 6. Maximum Output Voltage vs. RSDT Voltage
www.maximintegrated.com
Maxim Integrated │ 21
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
External Disconnect MOSFET Selection
33ms, the p-MOSFET has to sustain the highest input
voltage and the programmed current limit.
An external p-MOSFET can be used to disconnect the
boost output from the battery in the event of an output
overload or short condition. In the case of the SEPIC or
buck-boost, this protection is not necessary and in those
cases there is no need for the p-MOSFET. Connect the
PGATE pin to ground in the case of the SEPIC and buckboost. If it is necessary to have an output short protection
for the boost even at power-up, then the current through
the p-MOSFET (Figure 7) has to be sensed. Once the
current-sense voltage exceeds a certain threshold, it
should limit the input current to the programmed threshold.
This threshold should be set at a sufficiently high level so
that it never trips at startup or under normal operating conditions. Check the safe operating area of the p-MOSFET
so that the current-limit trip threshold and the voltage on
the MOSFET do not exceed the limits of the SOA curve of
the p-MOSFET at the highest operating temperature. The
current-limit protection circuit is active for 33ms before
the short trip threshold is triggered in the device, disconnecting the p-MOSFET from the input source. During the
Overvoltage Protection
The minimum overvoltage-protection threshold at the
DC-DC converter output (VOVP) is determined using the
following formula:
VOVPmin = (1.19 - OVP Hysteresis) x (1 + R1/R2)
volts (see Figure 2) where 1.19V is the minimum overvoltage threshold and OVP hysteresis is 70mV. Set this
minimum overvoltage threshold so that at 92% of this
threshold the circuit can still regulate the current in the
LED string when the forward-voltage drop on all the LEDs
in the LED string are at the maximum. Use the following
formula to calculate the minimum overvoltage-threshold
set point:
VLEDmax + 1 = 0.92 x VOVPmin
where VLEDmax is the maximum voltage drop that can
occur on LED string.
Q2
R11
VIN
C1
D1
L1
TO LED STRINGS
R12
D3
C7
C8
D2
Q1
R10
RCS
Q3
R7
RSCOMP
PGATE
IN
NDRV
CS
MAX16813B
Figure 7. External Disconnect MOSFET
www.maximintegrated.com
Maxim Integrated │ 22
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Feedback Compensation
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 capacitor
voltage. When the PWM dimming pulses are less than 24
switching clock cycles, the feedback loop regulates the
converter output voltage to 95% of the OVP threshold.
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 continuousconduction mode. The RHP zero adds a 20dB/decade
gain together with a 90° phase lag, which is difficult to
compensate.
The worst-case RHP zero frequency (fZRHP) is calculated
as follows:
For boost configuration:
VLED (1 − D MAX ) 2
2π × L × ILED
f ZRHP =
For SEPIC and coupled-inductor buck-boost configurations:
f ZRHP =
VLED (1 − D MAX ) 2
2π × L × ILED × D MAX
where fZRHP is in hertz, VLED is in volts, L is the
inductance value of L1 in henries, and ILED is in amperes.
A simple way to avoid this zero is to roll off the loop gain
to 0dB at a frequency less than 1/5 of the RHP zero
frequency with a -20dB/decade slope.
The switching converter small-signal transfer function
also has an output pole. The effective output impedance,
together with the output filter capacitance, determines the
output pole frequency (fP1) that is calculated as follows:
For boost configuration:
fP1 =
ILED
2 × π × VLED × C OUT
For SEPIC and coupled-inductor buck-boost configurations:
ILED × D MAX
fP1 =
2 × π × VLED × C OUT
www.maximintegrated.com
where fP1 is in hertz, VLED is in volts, ILED is in amperes,
and COUT is in farads. Compensation components
(RCOMP and CCOMP) perform two functions. CCOMP
introduces a low-frequency pole that presents a -20dB/
decade slope to the loop gain. RCOMP flattens the gain
of the error amplifier for frequencies above the zero
formed by RCOMP and CCOMP. For compensation, this
zero is placed at the output pole frequency (fP1) so that it
provides a -20dB/decade slope for frequencies above fP1
to the combined modulator and compensator response.
The value of RCOMP needed to fix the total loop gain at
fP1, so that the total loop gain crosses 0dB with -20dB/
decade slope at 1/5 the RHP zero frequency, is calculated
as follows:
For boost configuration:
f ZRHP × R CS × ILED
R COMP =
5 × fP1 × GM COMP × VLED × (1 − D MAX )
For SEPIC and coupled-inductor buck-boost configurations:
R COMP =
f ZRHP × R CS × ILED × D MAX
5 × fP1 × GM COMP × VLED × (1 − D MAX )
where RCOMP is the compensation resistor in ohms,
fZRHP and fP1 are in hertz, RCS is the switch current-sense
resistor in ohms, and GMCOMP is the transconductance
of the error amplifier (600μS).
The value of CCOMP is calculated as follows:
C COMP =
1
2π × R COMP × f Z1
where fZ1 is the compensation zero placed at 1/5 of
the crossover frequency that is, in turn, set at 1/5 of the
fZRHP. If the output capacitors do not have low ESR, the
ESR zero frequency may fall within the 0dB crossover
frequency. 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 parallel
with CCOMP and RCOMP. Figure 5 shows the SEPIC
configuration and Figure 4 shows the coupled-inductor
buck-boost configuration.
Design Verification
The following criteria must be satisfied before the design
can go into production:
1) The chosen inductor must not saturate at the lowest
input line voltage and the maximum output current
condition. The inductor must not saturate at the highest operating case temperature. Adequate margin
should be provided.
Maxim Integrated │ 23
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
2) Verify that the slope compensation is adequate.
Inadequate slope compensation can cause subharmonic oscillation. For more information on selecting the proper slope-compensation resistor, see the
SSlope Compensation section.
3) At the lowest input line voltage and the maximum
power condition, the signal on the CS pin should be
close to the current-limit voltage on the CS pin.
4) Select Schottky diodes, MOSFETs, and resistors that
meet the power and voltage ratings.
on the boost will change. The boost output voltage drops
when there is a transition from low dim to normal dim
made. If the closed-loop phase margin is less than 45°,
the output voltage might ring when the transition from LO
dim to normal dim occurs. This can cause flicker of the
LEDs and this flicker needs to be prevented by increasing
the phase margin. If the flicker is still present even when
the phase margin exceeds 60°, it may be necessary to
increase the output capacitor.
5) Select input and output capacitors that meet ripplevoltage and ripple-current requirements.
TEST
RINJ
6) Set the overvoltage at the appropriate point.
Loop-Stability Verification
REF
To verify the loop stability, it is a good idea to use a loop
analyzer to study the closed-loop gain and phase with
frequency. To check the closed-loop gain, connect the
test and reference probes of the analyzer, as shown in
Figure 8.
The crossover frequency (fC) in the design is 12kHz and
the phase margin is 74°. It is important to verify the loop
stability and phase margin before the design goes into
production. The typical crossover frequency should be in
the range of fSW /10 > fC > fSW /20 where fC is the crossover frequency. The phase margin should exceed 60° if
possible. It is also important to check the performance of
the design at the transition point from low dim to high dim
and vice versa. When the device is switching over from
low DIM mode to normal DIM mode, the output voltage
R1
C2
LED
STRINGS
R2
TO OVP
TO OUT1
TO OUT2
TO OUT3
TO OUT4
Figure 8. Loop Analyzer Connection to MAX16813B Circuit
100
200
TR1: MAG (GAIN)
80
150
TR2: PHASE (GAIN)
60
100
40
TR1/dB
Check the voltages on the OUT_ pins with dimming at
100% duty cycle. Then insert a diode and the injection
resistor in the string where the OUT_ voltage is closest
to 1V. The added diode in series with the LED string
keeps the string where the injection resistor is added as
the string that controls the output voltage. Use an injection transformer to insert the injection voltage from test to
ref. The loop analyzer can plot the gain and phase of the
closed loop where the loop gain is TJW/RJW. The crossover frequency occurs at the frequency where the gain is
0db. The phase margin at that frequency should exceed
45° for guaranteed stable operation. The optimum phase
margin should exceed 60°. An example of the closed-loop
gain and phase margin on a MAX16813B boost is shown
in Figure 9. This measurement was done on the typical
application shown in Figure 2 at an input voltage of 12V.
1N4148W
OUTPUT
20
50
0
0
-20
-50
-40
-100
-60
-150
-80
-100
TR2/°
7) After the compensation values are designed, verify the
design by measuring the loop stability.
102
103
104
f/Hz
105
-200
Figure 9. Closed-Loop Gain and Phase Margin
www.maximintegrated.com
Maxim Integrated │ 24
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Analog Dimming Using External
Control Voltage
Connect a resistor (RSETI2) to the SETI input as shown in
Figure 10 for controlling the LED string current using an
external control voltage. The device applies a fixed 1.23V
bandgap reference voltage at SETI and measures the
current through SETI. This measured current 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 external control voltage to SETI through the resistor
(RSETI2). The resulting change in the LED current with
the control voltage is linear and inversely proportional.
The LED current control range remains between 20mA
to 150mA.
Use the following equation to calculate the LED current
set by the control voltage applied:
1500 (1.23 − VC )
I OUT = +
× 1220
R SETI
R SETI2
PCB Layout Considerations
LED driver circuits based on the MAX16813B 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 switchingconverter 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 VCC as close as
possible to the device 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.
2) Have a power ground plane for the switching-converter
power circuit under the power components (input filter
capacitor, output filter capacitor, inductor, MOSFET,
www.maximintegrated.com
rectifier diode, and current-sense resistor). Connect
PGND to the power ground plane as close as possible
to PGND. Connect all other ground connections to the
power ground plane using vias close to the terminals.
3) There are two loops in the power circuit that carry
high-frequency switching currents. One loop is when
the MOSFET is on (from the input filter capacitor
positive terminal, through the inductor, the internal
MOSFET, and the current-sense resistor, to the input
capacitor negative terminal). The other loop is when
the MOSFET is off (from the input capacitor positive
terminal, through the inductor, the rectifier diode,
output filter capacitor, to the input capacitor negative terminal). Analyze these two loops and make the
loop areas as small as possible. Wherever possible,
have a return path on the power ground plane for the
switching currents on the top-layer copper traces, or
through power components. This reduces the loop
area considerably and provides a low-inductance path
for the switching currents. Reducing the loop area also
reduces radiation during switching.
4) Connect the power ground plane for the constantcurrent LED driver portion of the circuit to LEDGND
as close as possible to the device. Connect SGND to
PGND at the same point.
MAX16813B
1.23V
SETI
RSETI2
RSETI
VC
Figure 10. Analog Dimming with External Control Voltage
Maxim Integrated │ 25
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Chip Information
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX16813BATP/V+
-40°C to +125°C
20 TQFN-EP*
MAX16813BAUP/V+
-40°C to +125°C
20 TSSOP-EP*
PROCESS: CMOS
/V denotes an automotive qualified part.
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
www.maximintegrated.com
Maxim Integrated │ 26
MAX16813B
Integrated, 4-Channel, High-Brightness
LED Driver with High-Voltage DC-DC Controller
and Battery Disconnect
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
0
8/17
Initial release
—
1
1/18
Removed future product status from MAX16813BAUP/V+ in Ordering Information
26
DESCRIPTION
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.
© 2018 Maxim Integrated Products, Inc. │ 27
工商网监
湘ICP备2023018690号
