MAXIM MAX17129

19-5676; Rev 1; 9/11
TION KIT
EVALUA BLE
IL
AVA A
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
The MAX17129/MAX17149 are high-efficiency drivers
for white LEDs. They are designed for small- to mediumsized LCDs that employ an array of LEDs as the light
source. An internal switch step-up controller with QuickPWMK drives the LED array, which can be configured for
up to 6 strings in parallel and either 11 LEDs (MAX17129)
or 6 LEDs in series (MAX17149) per string. Each string
is terminated with a ballast that achieves Q2% currentregulation accuracy, ensuring even LED brightness and
provides an adjustable 10mA to 45mA full-scale LED
current. The devices have a wide input voltage range of
6V to 26V. The MAX17129 integrates an LDO to simplify
applications that have a single high-voltage supply. The
devices also feature a low-input-voltage mode for applications that have a 3V to 5.5V supply voltage.
The devices support both PWM and hybrid dimming
mode. In PWM dimming mode, the external PWM signal
directly controls the brightness of LEDs. The dimming
frequency ranges from 100Hz to 25kHz with 400ns minimum on-time. In hybrid dimming mode, the LED current
amplitude can be adjusted to 25% of full-scale LED current to improve system efficiency when brightness is low.
The devices have multiple features to protect the controller from fault conditions. Separate voltage-feedback
loops limit the output voltage to safe operation. The open
and short-LED detection shuts down the faulty string
while keeping other strings operating normally.
The devices feature cycle-by-cycle current limit on the
internal switch to provide consistent operation and softstart capability. If the devices are in current-limit condition, the step-up converter is latched off after an internal
timer expires. A thermal-shutdown circuit provides another level of protection and prevents ICs from damage.
The ICs’ step-up controller features an internal 0.25I (typ),
48V (max) power MOSFET with lossless current sense and
accurate cycle-by-cycle current limit. The Quick-PWM control architecture provides fast load-transient response without requiring an external loop compensation component,
simplifies the external circuitry, and saves board area. The
Quick-PWM control scheme has constant off-time and
adjustable pseudo-fixed frequency, which enables a wide
variety of applications that can trade off component size
for operating frequency. Low feedback voltage at each
LED string (275mV typ at 20mA LED current) helps reduce
power loss and improve efficiency.
The ICs are available in a 16-pin, thin QFN package with
0.5mm lead spacing. The package is 3mm x 3mm with a
maximum thickness of 0.8mm for ultra-thin LCD panel design.
Features
S 3V to 26V Input Supply Voltage
S Up to Six Parallel Strings of Multiple SeriesConnected LEDs
S Step-Up Regulator with Quick-PWM Control Scheme
S Two-Level Selectable Switching Frequency
S 0.25I Internal HV Power MOSFET (48V max)
S Low String Feedback Voltage: 275mV at 20mA
LED Current
S Full-Scale LED Current Adjustable from 10mA to
45mA
S ±2% Current Regulation Accuracy Between Strings
S Support PWM and Hybrid Dimming Mode
S 100:1 Dimming Ratio
S 100Hz to 25kHz Dimming Frequency for PWM
Dimming Mode
S Open and Short LED Protection
S Output Overvoltage Protection
S Small 16-Pin, 3mm x 3mm Thin QFN Package
Applications
Notebook, Subnotebook, and Tablet Computer
Displays
Automotive Systems
Handy Terminals
Ordering Information
PART
MAX17129ETE +
TEMP RANGE
PIN-PACKAGE
-40°C to +85°C
16 Thin QFN-EP*
16 Thin QFN-EP*
-40°C to +85°C
+Denotes lead(Pb)-free/RoHS-compatible package.
*EP = Exposed pad.
MAX17149ETE+
Simplified Operating Circuit appears at end of data sheet.
Quick-PWM is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ 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.
MAX17129/MAX17149
General Description
MAX17129/MAX17149
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
ABSOLUTE MAXIMUM RATINGS
FSEL, IN, BRT, EN to GND ...................................-0.3V to +28V
FB_, LX, OVP to PGND..........................................-0.3V to +48V
PGND to GND.......................................................-0.3V to +0.3V
VCC to GND..............................................................-0.3V to +6V
ISET to GND................................................ -0.3V to VCC + 0.3V
LX Switch Continuous RMS Current......................................1.6A
Continuous Power Dissipation (TA = +70NC)
16-Pin Thin QFN (derate 14.7mW/NC above +70NC)... 1176mW
Operating Temperature Range........................... -40NC to +85NC
Junction Temperature......................................................+150NC
Storage Temperature Range............................. -60NC to +150NC
ESD
HBM..................................................................................±2kV
MM................................................................................. ±200V
Lead Temperature (soldering, 10s).................................+300NC
Soldering Temperature (reflow).......................................+260NC
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.
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1. VIN = 12V, RISET = 100kI, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25NC.) (Note 1)
PARAMETER
IN Input Voltage Range
CONDITIONS
IN not connected to VCC
IN connected to VCC
MIN
TYP
MAX
6
26
3.0
5.5
UNITS
V
VEN = 3V, VIN = 26V, no external loads
3.2
4
mA
0.1
5
µA
VCC Output Voltage
VEN = 0V, VIN = 26V
VEN = 3V, 0 < IVCC < 10mA
3.6
3.8
4.0
V
VCC Current Limit
VCC is forced to 3.5V; IN not connected to VCC
15
30
45
mA
VCC UVLO Threshold
Rising edge, typical hysteresis = 100mV
2.75
2.8
2.85
V
IN UVLO Threshold
Rising edge, typical hysteresis = 100mV;
IN not connected to VCC
5.5
5.75
5.9
V
IN Standby Current
STEP-UP CONVERTER
LX On-Resistance
100mA from LX to PGND
250
500
mω
LX Leakage Current
VLX = 40V, TA = +25NC
FSEL = GND, VIN = 12V, VOVP = 22V
0.05
1
µA
450
500
550
FSEL = VCC, VIN = 12V, VOVP = 22V
900
1000
1100
Duty cycle = 75%
2.5
3
3.5
Off-Time
LX Peak Current Limit
Minimum On-Time
50
Minimum Output Regulation
Voltage
MAX17129 only
15
16.5
Maximum Output Regulation
Voltage
MAX17149 only
6.8
MAX17129 only
41.5
MAX17149 only
23.9
ns
A
ns
18
V
8.3
9.8
V
43
44.5
V
25.4
26.9
V
INPUT LEAKAGE/BIAS CURRENTS
EN Bias Current
BRT Bias Current
0.3V < VEN < 3.5V, TA = +25°C
6
4.1V < VEN < 26V, TA = +25°C
110
0.3V < VBRT < 3.5V, TA = +25°C
15
4.1V < VBRT < 26V, TA = +25°C
2000
EN Input Impedance
OVP Input Current
FSEL Bias Current
2
750
1500
µA
µA
kω
MAX17129 only; VOVP = 40V, VFB = 0.75V
15
50
µA
MAX17149 only; VOVP = 20V, VFB = 0.75V
7.5
25
µA
0.3V < VFSEL < 3.5V, TA = +25°C
4.1V < VFSEL < 26V, TA = +25°C
6
2000
µA
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
(Circuit of Figure 1. VIN = 12V, RISET = 100kI, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25NC.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
250
kω
LED CURRENT SOURCE
ISET Resistance Range
Full-Scale FB_ Output Current
44
RISET = 44.44kω
43.3
45
47.7
RISET = 66.66kω
29.1
30
30.9
RISET = 100kω
19.4
20
20.6
RISET = 133.33kω
14.55
15
15.45
RISET = 200kω
9.65
10
10.35
RISET = 100kω, hybrid dimming mode
4.4
5
5.6
RISET = 250kI, hybrid dimming mode
1.4
2
2.6
1.225
1.250
1.275
ISET Output Voltage
Current Regulation Between
Strings
Minimum FB_ Regulation Voltage
IFB_ = 30mA
-1.5
+1.5
IFB_ = 20mA
-2.0
+2.0
IFB_ = 15mA
-2.0
+2.0
IFB_ = 10mA
-2.75
+2.75
IFB_ = 5mA, hybid dimming ode
-6.0
+6.0
IFB_ = 2mA, hybrid dimming mode
-15.0
+15.0
RISET = 66.66kI, 100% duty cycle
375
550
RISET = 100kI, 100% duty cycle
275
365
RISET = 133.33kI, 100% duty cycle
200
275
RISET = 200kI, 100% duty cycle
125
200
FB_ On-Resistance
VFB_ = 50mV
FB_ Leakage Current
VFB_ = 28V, TA = +25°C, EN = 0V, VOVP = 28V
VFB_ = 40V, TA = +25°C, EN = 0V, VOVP = 40V
20
FB_ On-Time
300
BRT Input High Level
2.1
0.05
1
2.5
5
EN Input High Level
2.1
MAX17129/MAX17149 enabled, hybrid dimming mode
1.4
%
mV
ω
µA
V
0.1
MAX17129/MAX17149 enabled, PWM dimming mode
V
ns
BRT Input Low Level
BRT Dimming Frequency
mA
0.8
V
25
kHz
1.8
EN Input Low Level
0.8
V
V
FAULT PROTECTION
OVP Overvoltage
Rising edge, hysteresis = 1.8V
FB_ Check LED Source Current
FB_ Check LED Time
44.1
45.1
46.1
V
0.60
0.665
0.73
mA
Sequence for 6 channels
1
FB_ Open LED Threshold
FB_ Overvoltage Threshold
6.7
ms
500
700
8.0
9.6
mV
V
Thermal-Shutdown Threshold
(Note 2)
+160
°C
Thermal-Shutdown Hysteresis
(Note 2)
15
°C
BOOST FREQUENCY SELECTION FSEL
FSEL Input High Level
Select fSW = 500kHz
FSEL Input Low Level
Select fSW = 1000kHz
2.1
V
0.8
V
3
MAX17129/MAX17149
ELECTRICAL CHARACTERISTICS (continued)
MAX17129/MAX17149
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1. VIN = 12V, RISET = 100kI, TA = -40NC to +85NC, unless otherwise noted.) (Note 1)
PARAMETER
IN Input Voltage Range
CONDITIONS
MIN
TYP
MAX
IN not connected to VCC
6
26
IN = VCC
3
5.5
UNITS
V
VEN = 3V, VIN = 26V, no external loads
4
mA
5
µA
VCC Output Voltage
VEN = 0V, VIN = 26V
VEN = 3V, 0 < IVCC < 10mA
3.6
4.0
V
VCC Current Limit
VCC is forced to 3.5V; IN not connected to VCC
15
45
mA
VCC UVLO Threshold
Rising edge, typical hysteresis = 100mV
2.75
2.85
V
IN UVLO Threshold
Rising edge, typical hysteresis = 100mV;
IN not connected to VCC
5.5
5.9
V
500
mω
1
FA
IN Quiescent Current
STEP-UP CONVERTER
LX On-Resistance
100mA from LX to PGND
LX Leakage Current
VLX = 40V, TA = +25NC
FSEL = GND VIN = 12V, VOVP = 22V
450
550
FSEL = VCC, VIN = 12V, VOVP = 22V
900
1100
LX Peak Current Limit
Duty cycle = 75%
2.5
3.65
A
Minimum Output Regulation
Voltage
MAX17129 only
15
18
V
MAX17149 only
6.8
9.8
V
Maximum Output Regulation
Voltage
MAX17129 only
41.5
44.5
V
MAX17149 only
23.9
26.9
V
Off-Time
ns
INPUT LEAKAGE/BIAS CURRENTS
EN Bias Current
BRT Bias Current
0.3V < VEN < 3.5V, TA = +25°C
6
4.1V < VEN < 26V, TA = +25°C
110
0.3V < VBRT < 3.5V, TA = +25°C
15
4.1V < VBRT < 26V, TA = +25°C
2000
EN Input Impedance
OVP Input Current
FSEL Bias Current
750
µA
µA
kω
MAX17129 only; VOVP = 40V, TA = +25°C, VFB = 0.75V
50
MAX17149 only; VOVP = 20V, TA = +25°C, VFB = 0.75V
25
0.3V < VFSEL < 3.5V
6
4.1V < VFSEL < 26V
2000
µA
µA
LED CURRENT SOURCE
ISET Resistance Range
Full-Scale FB_ Output Current
44
250
RISET = 44.44kω
43.3
47.7
RISET = 66.66kω
29.1
30.9
RISET = 100kω
19.4
20.6
RISET = 133.33kω
14.55
15.45
RISET = 200kω
9.65
10.35
RISET = 100kω, hybrid dimming mode
4.4
5.6
RISET = 250kω, hybrid dimming mode
ISET Output Voltage
4
1.4
2.6
1.225
1.275
kω
mA
V
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
MAX17129/MAX17149
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1. VIN = 12V, RISET = 100kI, TA = -40NC to +85NC, unless otherwise noted.) (Note 1)
PARAMETER
Current Regulation Between
Strings
Minimum FB_ Regulation Voltage
FB_ On-Resistance
FB_ Leakage Current
CONDITIONS
MIN
TYP
MAX
IFB_ = 30mA
-1.5
+1.5
IFB_ = 20mA
-2.0
+2.0
IFB_ = 15mA
-2.0
+2.0
IFB_ = 10mA
-2.75
+2.75
IFB_ = 5mA, hybrid dimming mode
-6.0
+6.0
IFB_ = 2mA, hybrid dimming mode
-15.0
+15.0
RISET = 66.66kω, 100% duty cycle
550
RISET = 100kω, 100% duty cycle
365
RISET = 133.33kω, 100% duty cycle
275
RISET = 200kω, 100% duty cycle
200
VFB_ = 50mV
20
VFB_ = 28V, TA = +25°C, EN = GND, VOVP = 28V
1
VFB_ = 40V, TA = +25°C, EN = GND, VOVP = 40V
5
UNITS
%
mV
ω
µA
FB_ On-Time
300
ns
BRT Input High Level
2.1
V
BRT Input Low Level
BRT Dimming Frequency
EN Input High Level
0.1
MAX17129/MAX17149 enabled, PWM dimming mode
2.1
MAX17129/MAX17149 enabled, hybrid dimming mode
1.4
EN Input Low Level
0.8
V
25
kHz
1.8
0.8
V
V
FAULT PROTECTION
OVP Overvoltage
Rising edge, hysteresis = 1.8V
FB_ Check LED Source Current
44.1
46.1
V
0.60
0.73
mA
700
mV
9.7
V
FB_ Open LED Threshold
FB_ Overvoltage Threshold
6.7
BOOST FREQUENCY SELECTION FSEL
FSEL Input High Level
Select fSW = 500kHz
FSEL Input Low Level
Select fSW = 1000kHz
2.1
V
0.8
V
Note 1: All devices are 100% production tested at TA = +25NC. Limits over temperature are guaranteed by design.
Note 2: Specifications are guaranteed by design, not production tested.
5
Typical Operating Characteristics
(Circuit of Figure 1. VIN = 12V, TA = +25°C, unless otherwise noted.)
BOOST CONVERTER EFFICIENCY
vs. BRIGHTNESS
(VIN = 12V, VOUT = 31.8V/IOUT = 120mA
AT 100%)
80
EFFICIENCY (%)
90
88
86
84
82
15
LED CURRENT (mA)
92
LED CURRENT vs. BRIGHTNESS SETTING
20
MAX17129 toc02
90
MAX17129 toc01
94
MAX17129 toc03
BOOST CONVERTER EFFICIENCY
vs. INPUT VOLTAGE
(VOUT = 31.8V/IOUT = 120mA,
BRIGHTNESS = 100%)
EFFICIENCY (%)
70
10
60
5
fBRT = 200Hz
80
78
50
8
11
14
17
20
INPUT VOLTAGE (V)
23
0
26
0
20
40
60
80
BRIGHTNESS (%)
2.06
2.04
LED CURRENT (mA)
20.15
20.10
20.05
80
2.02
2.00
20.00
1.98
5
8
11
14
17
20
23
26
5
8
11
14
17
20
23
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
IN QUIESCENT CURRENT
vs. IN VOLTAGE
STARTUP WAVEFORMS
(BRIGHTNESS = 100%)
26
MAX17129 toc07
MAX17129 toc06
6
5
VEN
5V/div
0V
VLX
50V/div
0V
INDUCTOR
CURRENT
500mA/div
0A
100% BRIGHTNESS
4
3
200Hz /1% BRIGHTNESS
2
VOUT
20V/div
1
12V
0
5
8
11
14
17
IN VOLTAGE (V)
6
60
LED CURRENT (ILED = 20mA AT
10% BRIGHTNESS) vs. INPUT VOLTAGE
MAX17129 toc04
20.20
40
PWM DUTY CYCLE (%)
LED CURRENT (ILED = 20mA AT
100% BRIGHTNESS) vs. INPUT VOLTAGE
LED CURRENT (mA)
20
100
MAX17129 toc05
5
IN QUIESCENT CURRENT (mA)
MAX17129/MAX17149
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
20
23
26
0V
4ms/div
100
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
SWITCHING WAVEFORMS
(VIN = 12V, BRIGHTNESS = 100%)
STARTUP WAVEFORMS
(BRIGHTNESS = 20%)
MAX17129 toc09
MAX17129 toc08
VEN
5V/div
0V
VLX
50V/div
0V
INDUCTOR
CURRENT
500mA/div
0A
VLX
20V/div
0V
INDUCTOR
CURRENT
500mA/div
VOUT
20V/div
12V
0mA
0V
4ms/div
1µs/div
LED OPEN FAULT PROTECTION
(BRIGHTNESS = 100%, LED OPEN ON FB1)
LED SHORT FAULT PROTECTION
(BRIGHTNESS = 100%,
3 LEDS SHORT ON FB1)
MAX17129 toc11
MAX17129 toc10
VFB1
1V/div
0V
VFB2
10V/div
0V
31.8V
VOUT
10V/div
IFB2
10mA/div
0mA
20mA
2ms/div
VFB1
10V/div
0V
IFB1
20V/div
0mA
20mA
IFB2
20mA/div
0mA
20mA
2ms/div
7
MAX17129/MAX17149
Typical Operating Characteristics (continued)
(Circuit of Figure 1. VIN = 12V, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(Circuit of Figure 1. VIN = 12V, TA = +25°C, unless otherwise noted.)
LINE TRANSIENT RESPONSE
(VIN = 9V↔21V, BRIGHTNESS = 100%)
LINE TRANSIENT RESPONSE
(VIN = 21V↔9V, BRIGHTNESS = 100%)
MAX17129 toc12
MAX17129 toc13
9V
9V
VIN
10V/div
VOUT
(AC-COUPLED)
500mV/div
0V
INDUCTOR
CURRENT
500mA/div
0A
IFB1
20mA/div
0mA
21V
20mA
20mA
200µs/div
MAXIMUM UNBALANCE RATE
BETWEEN STRINGS vs. BRIGHTNESS
(VIN = 12V, fBRT = 200Hz, ILED = 20mA)
MAXIMUM UNBALANCE RATE
BETWEEN STRINGS
(ILED = 20mA AT 100% BRIGHTNESS)
vs. INPUT VOLTAGE
0.6
0.4
0.2
0
10
20
30
40
50
IFB_-IFB(AVG) MAX
IFB(AVG)
60
70
BRIGHTNESS (%)
80
90 100
MAX17129 toc15
0.8
MAXIMUM UNBALANCE RATE (%)
MAX17129 toc14
0.8
MAX. UNBALANCE
=
RATE (%)
8
VIN
10V/div
VOUT
(AC-COUPLED)
200mV/div
0V
INDUCTOR
CURRENT
500mA/div
0A
IFB1
20mA/div
0mA
21V
100µs/div
1.0
MAXIMUM UNBALANCE RATE (%)
MAX17129/MAX17149
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
0.7
0.6
0.5
0.4
0.3
MAX. UNBALANCE
=
RATE (%)
IFB_-IFB(AVG) MAX
IFB(AVG)
0.2
6
9
12
15
18
INPUT VOLTAGE (V)
21
24
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
FB5
FB4
FB3
FB2
TOP VIEW
12
11
10
9
FB6 13
GND 14
MAX17129
MAX17149
ISET 15
EP
2
3
4
FSEL
BRT
1
IN
+
VCC
EN 16
8
FB1
7
OVP
6
PGND
5
LX
THIN QFN
3mm × 3mm
Pin Description
PIN
NAME
FUNCTION
BRT
PWM Signal Input. This PWM signal controls the LED brightness by turning the LED current sources on
or off.
VCC
Internal LDO Output. VCC provides bias supply to the devices. VCC is generated by internal LDO.
Connect a minimum 1FF capacitor from VCC to GND. All power outputs are disabled until VCC
exceeds its UVLO threshold. See the Input Supply Voltage Configuration and UVLO section for supply
configurations for the ICs.
3
IN
Supply Input. Connect IN to the system input supply voltage and bypass IN to GND with a minimum
0.1FF ceramic capacitor. The ICs are disabled if VIN falls below its UVLO threshold. The devices can
extend the operating range down to 3.0V if IN and VCC are tied together. See the Input Supply Voltage
Configuration and UVLO section.
4
FSEL
5
LX
6
PGND
7
OVP
Boost Output Voltage-Sensing Input. This voltage is used for overvoltage protection.
8
FB1
Current-Balancer Output. LED string cathode connection. FB1 is the open-drain output of an internal
regulator, which controls current through FB1. FB1 can sink up to 45mA. If unused, connect FB1 to
GND or leave high impedance.
9
FB2
Current-Balancer Output. LED string cathode connection. FB2 is the open-drain output of an internal
regulator, which controls current through FB2. FB2 can sink up to 45mA. If unused, connect FB2 to
GND or leave high impedance.
1
2
Step-Up Converter Switching Frequency Selection Input. Connect to VCC with a 10kω resistor to set
500kHz, or connect to GND to set 1MHz.
Step-Up Regulator Switching Node. Connect inductor and output diode here and minimize trace area
for lowest EMI.
Power Ground
9
MAX17129/MAX17149
Pin Configuration
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
MAX17129/MAX17149
Pin Description (contineud)
PIN
FUNCTION
10
FB3
Current-Balancer Output. LED string cathode connection. FB3 is the open-drain output of an internal
regulator, which controls current through FB3. FB3 can sink up to 45mA. If unused, connect FB3 to
GND or leave high impedance.
11
FB4
Current-Balancer Output. LED string cathode connection. FB4 is the open-drain output of an internal
regulator, which controls current through FB4. FB4 can sink up to 45mA. If unused, connect FB4 to
GND or leave high impedance.
12
FB5
Current-Balancer Output. LED string cathode connection. FB5 is the open-drain output of an internal
regulator, which controls current through FB5. FB5 can sink up to 45mA. If unused, connect FB5 to
GND or leave high impedance.
13
FB6
Current-Balancer Output. LED string cathode connection. FB6 is the open-drain output of an internal
regulator, which controls current through FB6. FB6 can sink up to 45mA. If unused, connect FB6 to
GND or leave high impedance.
14
GND
Analog Ground. Connect to ISET resistor ground as close as possible.
ISET
Full-Scale LED Current Adjustment Pin. The resistance from ISET to GND controls the full-scale current
in each LED string:
ILED_FS = 20mA O 100kI/RISET
The acceptable resistance range is 44.44kI < RISET < 200kI, which corresponds to full-scale LED
current of 45mA > ILED_FS > 10mA.
15
10
NAME
16
EN
Enable and Dimming Mode Selection Input. Pull EN higher than 2.1V to enable the device, and lower
than 0.8V to disable the device. When VEN is higher than 2.1V, direct PWM mode is selected; when VEN
is between 1.4V and 1.8V, hybrid dimming mode is selected. While selecting hybrid dimming mode, the
device first needs to be enabled.
—
EP
Exposed Backside Pad. Solder to the circuit board ground plane with sufficient copper connection to
ensure low thermal resistance. See the PCB Layout Guidelines section.
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
VIN
6V TO 26V
MAX17129/MAX17149
L1
10µH
D1
C2
2.2µF
C1
2.2µF
CIN
4.7µF
FSEL
LX
IN
0.1µF
PGND
VCC
MAX17129
1µF
ISET
OVP
RISET
100kI
FB1
FB2
FB3
EN
FB4
100Hz TO 25kHz
BRT
FB5
FB6
GND
EP
Figure 1. MAX17129 Typical Operating Circuit
Typical Operating Circuit
Table 1. Component List
DESIGNATION
DESCRIPTION
CIN
4.7FF Q10%, 25V X5R ceramic capacitor
(1206)
Murata GRM319R61E475KA12D
C1, C2
2.2FF Q20%,50V X7R ceramic capacitors
(1206)
Murata GRM31CR71H225K
D1
2A, 40V Schottky diode (M-flat)
Toshiba CMS11
L1
10FH, 1.5A, H = 1.2mm
VLP6812T-100M1R5
White LED
3.2V (typ), 3.5V (max) at 20mA
Nichia NSSW008C
The MAX17129 typical operating circuit is shown in
Figure 1. Table 1 lists some recommended components,
and Table 2 lists the contact information for component
suppliers.
Table 2. Component Suppliers
SUPPLIER
PHONE
WEBSITE
Murata Electronics
North America, Inc.
770-436-1300 www.murata.com
Nichia Corp.
248-352-6575 www.nichia.com
Sumida Corp.
847-545-6700 www.sumida.com
Toshiba America
Electronic
Components, Inc.
949-623-2900 www.toshiba.com/taec
Vishay
402-563-6866 www.vishay.com
11
MAX17129/MAX17149
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
EN
45V
40.8V
OUTPUT
OVERVOLTAGE
STARTUP
IN
OVP
3.8V LDO
LOGIC-CIRCUIT
SUPPLY
FSEL
LX
CONTROL
AND
DRIVER
LOGIC
VCC
OFF-TIME
ONE-SHOT
tON /tOFF
CALCULATION
CURRENT
SENSE
N
PGND
LX
8V
FAULT
CONTROL
HVC
OVERVOLTAGE
THERMAL
SHUTDOWN
LVC
GM
FB6
FB5
FB4
FB3
FB2
VSAT
ERROR
AMP
FB1
ISET
ISET
EN
N
EN
FROM FAULT
CONTROL
BRT
DPWM
CONTROL
TEST AND OTP
SMBus
MAX17129
MAX17149
Figure 2. Functional Diagram
12
GND
CURRENT SOURCE
FB2
CURRENT SOURCE
FB3
CURRENT SOURCE
FB4
CURRENT SOURCE
FB5
CURRENT SOURCE
FB6
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
The MAX17129/MAX17149 are high-efficiency drivers for
arrays of white LEDs. They contain a Quick-PWM step-up
controller, a 3.8V linear regulator, PWM dimming control
circuit, internal power MOSFET, and six regulated current
sources. Figure 2 shows the devices' functional diagram.
When enabled, the step-up controller boosts the output
voltage to provide sufficient headroom for the current
sources to regulate their respective string currents. The
devices feature adjustable pseudo-fixed frequency,
which allows trade-offs between external component
size and operating efficiency.
Both devices have a wide input voltage range, from 6V
to 26V; when IN and VCC are tied together, the range is
extended to the 3V to 5.5V range.
Both devices can implement two different brightnesscontrol methods: PWM dimming and hybid dimming.
When in direct PWM mode, the LED brightness is controlled by the frequency and duty cycle of the squarewave signal applied on the BRT pin. When in hybrid
dimming mode, the amplitude of LED current is adjusted
to 25% of the full-scale value, which is set by the resistor
from the ISET pin to GND.
The devices have multiple features to protect the controller from faulty conditions. A separate feedback loop limits the output voltage in all circumstances. The devices
monitor each FB_ voltage during the operation. If one or
more strings are open, the corresponding FB_ voltages
are pulled below 700mV (max) and the OVP output is
forced to increase over the overvoltage threshold; once
the open fault is detected, the respective current sources
are so disabled. When one or more LEDs are shorted
and the related FB_ voltage exceeds 8V, short fault is
detected and the respective current source is disabled.
When in LED open or short conditions, only the faulty
string is disabled while other strings can still operate
normally.
The devices also feature other kinds of fault protections, which are overcurrent, output overvoltage, and
thermal shutdown. The cycle-by-cycle current limit is to
provide consistent operation and soft-start protection;
when in overcurrent condition, the devices latch off after
a 0.8ms typical (at full brighteness) overcurrent fault
timer expires. An output overvoltage protection prevents
the devices from switching when the output exceeds a
threshold voltage; A thermal-shutdown circuit prevents
the devices from excessive power dissipation.
Quick-PWM Step-Up Controller
The step-up converter is a Quick-PWM type for good
performance. The Quick-PWM control architecture is
a pseudo-fixed-frequency, constant-off-time, currentmode regulator. The control algorithm is simple: the
internal switch off-time is determined solely by a oneshot whose period is inversely proportional to output voltage, and directly proportional to input voltage. Figure 4
shows the functional diagram with Quick-PWM control
architecture. The off-time one-shot triggers when the
error comparator goes low, the inductor current is below
the current-limit threshold, and the minimum on-time
one-shot times out.
Once the step-up starts up, the output voltage is regulated by selecting the minimum FB voltage between the
detected active current-balancer outputs and comparing it to the OVP divider. The soft-start mechanism is
inserted to provide a controlled current profile during
step-up startup phases.
Off-Time One-Shot
The Quick-PWM core contains a fast, low-jitter, adjustable one-shot that sets the internal MOSFETs off-time.
The one-shot varies the off-time in response to the input
and feedback voltages. The internal switch off-time is
inversely proportional to the output voltage (VOVP), and
proportional to the input voltage (VIN):
TOFF =
VIN
VOVP × K
where the switching period (K) is set by the FSEL pin.
This algorithm results in a nearly constant switching
frequency and balanced inductor currents despite the
lack of a fixed-frequency clock generator. The benefits
of a near-constant switching frequency are two-fold: first,
the frequency can be selected to avoid noise-sensitive
regions; second, the inductor ripple-current operating
point remains relatively constant, resulting in easy design
methodology and predictable output-voltage ripple. The
off-time one-shots have good accuracy at the operating
points specified in the Electrical Characteristics table.
Off-times translate only roughly to switching frequencies.
The off-times guaranteed in the Electrical Characteristics
table are influenced by internal switching delays. Resistive
losses, including the inductor, internal MOSFET, the forward voltage of the output diode, output capacitor ESR,
and PCB copper losses in the output and ground tend to
raise the switching frequency at higher output currents.
13
MAX17129/MAX17149
Detailed Description
MAX17129/MAX17149
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
The actual switching frequency can be approximated by:
fs =
due to increased switching losses. Low-frequency operation offers the best overall efficiency but requires larger
components and PCB area.
VIN − IIN × R DSON
1
×
TOFF VOVP + VD − IIN × R DSON
Input Supply Voltage Configuration and
UVLO
where:
The devices include an internal low-dropout linear
regulator (VCC) and are disabled until VCC exceeds the
UVLO threshold. The hysteresis on UVLO is approximately 100mV. When VIN is higher than 6V with EN high,
this linear regulator generates a 3.8V supply to power
the internal PWM controller, control logic, and MOSFET
driver. The VCC voltage drops to 0V with EN low. When
the VCC and IN pins are connected together, the devices
can operate in a low input-voltage range from 3V to 5.5V.
VD is the forward voltage of the output diode.
RDSON is the on-resistance of the internal MOSFET.
The switching frequency is adjustable by changing the
off-time at each supply turn-on cycle. As mentioned
above, it is implemented by changing the voltage level
of the FSEL pin.
High-frequency operation optimizes the regulator for the
smallest component size at the expense of efficiency
VIN
EN
IN
LX
FSEL
OVP
ON- /OFF-TIME
CALCULATION
ONE-SHOT
OVP
SOFT-START
SS
ERROR
COMPARATOR
REF
CURRENT
SENSE
REF
FB
MAX17129
MAX17149
INT
Figure 4. MAX17129/MAX17149 Quick-PWM Control Functional Diagram
14
INTEGRATOR
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
Startup
At startup, the devices perform an LED check by pulling up each FB_ pin with a current source to determine
whether a string of LEDs are connected. If an FB_ pin
is not connected with LEDs, it is disabled. The process
takes approximately 1ms. Then the current sources are
turned on.
Shutdown
The devices can be placed into shutdown by pulling the
EN pin low; when in shutdown mode, the current consumption is 5FA max. In the devices, the VCC voltage
drops to 0V with EN low.
Overvoltage Protection
To protect the step-up regulator when the load is open,
or the output voltage becomes excessive for any reason, the devices feature a dedicated overvoltage feedback input by monitoring output (OVP). There are two
thresholds for OVP and they provide careful protections.
When the OVP voltage exceeds the 43V (typ) for the
MAX17129 or 25.4V for the MAX17149, an overvoltage
flag is set to enable the open-string detection. When
the OVP voltage exceeds 45.2V (typ), the internal power
MOSFET stops switching. This step-up regulator switch
is reenabled after the VOVP drops 1.8V (typ hysteresis)
below the protection threshold. This overvoltage protection feature ensures the step-up regulator fail-safe operation when the LED strings are disconnected from the
output. Considering overvoltage threshold and minimum
output regulation voltage, the MAX17149 is suitable for
3–6 LEDs per string and the MAX17129 is suitable for
6–11 LEDs per string.
Overcurrent Protection
When in overcurrent condition, the devices latch off after
a fault timer expires. If running at full brightness, the
timeout is approximately 0.8ms (typ). If dimming, this
timeout is dependent on the dimming frequency and
duty cycle: the sum of the on-time cycles, during which
the device is in overcurrent condition, must be 0.8ms
(typ) for the timeout to expire.
LED Current Sources
Maintaining uniform LED brightness and dimming capability is critical for backlight applications. The ICs are
equipped with a bank of six matched current sources.
These specialized current sources are accurate within
Q3% and match with each other within 2%. The LED
full-scale current is set through the ISET pin (10mA <
ILED_FS < 45mA).
The minimum voltage drop across each current source
is 275mV (typ) when the LED current is 20mA. The lowvoltage drop helps reduce dissipation while maintaining
sufficient compliance to control the LED current within
the required tolerances.
The LED current sources can be disabled by connecting
the respective FB_ pin to GND before startup. When the
devices are enabled, the controller scans settings for
all FB_ pins. If a FB_ pin is not tied to GND, an internal
circuit pulls this pin high, and the controller enables the
corresponding current source to regulate the string current. If the FB_ pin is tied to GND, the controller disables
the corresponding current regulator. The current regulator cannot be disabled by connecting the respective FB_
pin to GND after the IC is enabled.
All FB_ pins in use are combined to extract a lowest FB_
voltage (LVC) (see Figure 2). LVC is fed into the step-up
regulator’s error amplifier and is used to set the output
voltage.
LX
VIN
6V TO 26V
LX
IN
VCC
IN
MAX17129
MAX17149
VS
3.0V TO 5.5V
VCC
MAX17129
MAX17149
Figure 5. Supply Configurations for the MAX17129/MAX17149
15
MAX17129/MAX17149
Figure 5 shows possible supply connection configurations for the devices. The VCC pin should be bypassed
to GND with a minimum 1FF ceramic capacitor.
MAX17129/MAX17149
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
Current-Source Fault Protection
An LED fault open/short is detected after the startup.
When one or more strings fail after the startup, the corresponding current source is disabled. The remaining LED
strings still operate normally.
LED Short and String Mismatch Protection
The devices can tolerate a slight mismatch between LED
strings. When severe mismatches or WLED shorts occur,
the FB_ voltages are uneven because of mismatched
voltage drop across strings. When FB_ voltage is higher
than 8V (typ) after LED turn on, an LED short is detected.
The remaining LED strings can still operate normally.
Open Current-Source Protection
The devices’ step-up regulator output voltage is regulated according to the minimum FB_ voltages on all
the strings in use. If one or more strings are open, the
respective FB_ pins are pulled to ground. For any FB_
lower than 700mV (max), the corresponding current
source is disabled. The remaining LED strings can
still operate normally. If all strings in use are open, the
devices shut the step-up regulator down.
PWM Dimming Control
The devices perform brightness control with the BRT
input signal. The current in the LEDs follows the duty
cycle and frequency of the BRT signal. The dimming
frequency can be from 0.1kHz to 25kHz.
Full-Scale LED Current
The full-scale LED current ILED_FS is set by the resistor
connected from ISET to GND and:
ILED_FS =
20mA × 100kΩ
RISET
The acceptable resistance range for ISET is 44.44kI <
RISET < 200kI, which corresponds to a full-scale LED
current of 45mA > ILED_FS > 10mA.
Hybrid Dimming Mode
The devices can implement hybrid dimming by controlling the voltage on the EN pin (between 1.4V and 1.8V)
after the device is enabled. In hybrid dimming mode,
the LED current is 25% of the full-scale current set by
the resistor on the ISET pin. The purpose of this hybrid
dimming operation is to improve system efficiency by
reducing the current in the LEDs, therefore reducing the
forward drop in them.
Thermal Shutdown
The devices include a thermal-protection circuit. When
the junction temperature exceeds TJ = +160NC (typ), a
16
thermal sensor immediately activates the fault protection,
which shuts down the step-up regulator and all current
sources, allowing the devices to cool down. Once the
devices cool down by approximately 15NC, the ICs start
up automatically. The thermal-overload protection protects the devices in the event of fault conditions. For continuous operation, do not exceed the absolute maximum
junction temperature rating of TJ = +150NC.
Design Procedure
All the devices’ designs should be prototyped and tested
prior to production.
External component value choice is primarily dictated
by the output voltage and the maximum load current, as
well as maximum and minimum input voltages. Begin by
selecting an inductor value. Once the inductor is known,
choose the diode and capacitors.
Inductor Selection
The inductance, peak current rating, series resistance,
and physical size should all be considered when selecting an inductor. These factors affect the converter’s operating mode, efficiency, maximum output load capability,
transient response time, output voltage ripple, and cost.
The maximum output current, input voltage, output
voltage, and switching frequency determine the inductor value. Very high inductance minimizes the current
ripple, and therefore reduces the peak current, which
decreases core losses in the inductor and I2R losses in
the entire power path. However, large inductor values
also require more energy storage and more turns of wire,
which increase physical size and I2R copper losses. Low
inductor values decrease the physical size but increase
the current ripple and peak current. Finding the best
inductor involves the compromises among circuit efficiency, inductor size, and cost.
In choosing an inductor, the first step is to determine the
operating mode: continuous-conduction mode (CCM)
or discontinuous-conduction mode (DCM). When CCM
mode is chosen, the ripple current and the peak current
of the inductor can be minimized. If a small-size inductor
is required, DCM mode can be chosen. In DCM mode,
the inductor value and size can be minimized but the
inductor ripple current and peak current are higher than
those in CCM. The controller can be stable, but there is a
maximum inductor value requirement to ensure the DCM
operating mode. The equations used here include a constant LIR, which is the ratio of the inductor peak-to-peak
ripple current to the average DC inductor current at the
full-load current. The controller operates in DCM mode
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
Once a physical inductor is chosen, higher and lower
values of the inductor should be evaluated for efficiency
improvements in typical operating regions. The detailed
design procedure for CCM can be described as:
Calculate the approximate inductor value using the
typical input voltage (VIN), the maximum output current (IOUT(MAX)), the expected efficiency (ETYP) taken
from an appropriate curve in the Typical Operating
Characteristics, and an estimate of LIR based on the
above discussion:
IIN(DC,MAX) =
I OUT(MAX) × VOUT
Calculate the ripple current at that operating point and
the peak current required for the inductor:
(
VIN(MIN) × VOUT(MAX) − VIN(MIN)
L CCM × VOUT(MAX) × fSW

VIN(MIN) 
L DCM(MAX) = 1 −
×
 VOUT(MAX) 


VIN(MIN) 2 × η
2 × fSW × VOUT(MAX) × I OUT(MAX)
The peak inductor current in DCM is calculated with the
following equation:
IPEAK_DCM =
(
I OUT(MAX) × 2 × VOUT(MAX) − VIN(MIN)
L DCM × fSW × η
)
The inductor’s saturation current rating should exceed
IPEAK and the inductor’s DC current rating should
exceed IIN(DC,MAX). For good efficiency, choose an
inductor with less than 0.1I series resistance.
Considering the circuit with six 10-LED strings and
20mA LED full-scale current, the maximum load current
(IOUT(MAX)) is 120mA with a 32V output and a minimal
input voltage of 7V.
Choosing a CCM operating mode with LIR = 0.8 at 1MHz
and estimating efficiency of 85% at this operating point:
2
VIN(MIN) × ηMIN
Choose an available inductor value from an appropriate
inductor family. Calculate the maximum DC input current
at the minimum input voltage VIN(MIN), using conservation of energy and the expected efficiency at that operating point (EMIN) taken from an appropriate curve in the
Typical Operating Characteristics:
IRIPPLE =
DCM mode (or the minimum inductor value for CCM
mode) is calculated with the following equation:
)
I
IPEAK_CCM = IIN(DC,MAX) + RIPPLE
2
When DCM operating mode is chosen to minimize the
inductor value, the calculations are different from those
above in CCM mode. The maximum inductor value for
 7V   32V − 7V  0.85 
L CCM = 
 

 = 10.59µH
 32V   120mA × 1MHz  0.8 
A 10FH inductor is chosen and the peak inductor current
at minimum input voltage is calculated as follows:
IPEAK_CCM =
7V × (32V − 7V)
120mA × 32V
+
7V × 0.85
2 × 10µH × 32V × 1MHz
= 0.92A
Alternatively, choose a DCM operating mode by using
lower inductance and estimating efficiency of 85% at this
operating point. Since DCM has higher peak inductor
current at lower input, it causes current limit when the
parameters are not chosen properly. Considering the
case with six 10-LED strings and 20mA LED full-scale
current to prevent excessive switch current from causing
current limit:
7V 
(7V) 2 × 0.85

×
L DCM(MAX) = 1 −

 32V  2 × 1MHz × 32V × 120mA
= 4.24µH
17
MAX17129/MAX17149
when LIR is higher than 2.0, and it works in CCM mode
when LIR is lower than 2.0. The best trade-off between
inductor size and converter efficiency for step-up regulators generally has an LIR between 0.3 and 0.5. However,
depending on the AC characteristics of the inductor core
material and ratio of inductor resistance to other powerpath resistances, the best LIR can shift up or down. If the
inductor resistance is relatively high, more ripples can
be accepted to reduce the number of required turns and
increase the wire diameter. If the inductor resistance is
relatively low, increasing inductance to lower the peak
current can reduce losses throughout the power path. If
extremely thin high-resistance inductors are used, as is
common for LCD panel applications, an LIR higher than
2.0 can be chosen for DCM operating mode.
MAX17129/MAX17149
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
A 3.3FH inductor is chosen. The peak inductor current at
minimum input voltage is calculated as follows:
IPEAK_DCM =
120mA × 2 × 32V × (32V − 7V)
3.3uH × 1MHz × 0.85 × (32V)
= 1.46A
Output Capacitor Selection
The total output-voltage ripple has two components: the
capacitive ripple caused by the charging and discharging
on the output capacitor, and the ohmic ripple due to the
capacitor’s equivalent series resistance (ESR):
VRIPPLE = VRIPPLE(C) + VRIPPLE(ESR)
VRIPPLE(C) ≈
I OUT(MAX)  VOUT(MAX) − VIN(MIN) 


C OUT  VOUT(MAX) × fSW 
and:
VRIPPLE(ESR) ≈ IPEAK x RESR(COUT)
where IPEAK is the peak inductor current (see the
Inductor Selection section).
The output-voltage ripple voltage should be low enough
for the FB_ current-source regulation. The ripple voltage
should be less than 200mVP-P. For ceramic capacitors, the output-voltage ripple is typically dominated by
VRIPPLE(C). The voltage rating and temperature characteristics of the output capacitor must also be considered.
Rectifier Diode Selection
The devices’ high switching frequency demands a highspeed rectifier. Schottky diodes are recommended for
most applications because of their fast recovery time
and low forward voltage. The diode should be rated to
handle the output voltage and the peak switch current.
Make sure that the diode’s peak current rating is at least
IPEAK calculated in the Inductor Selection section and
that its breakdown voltage exceeds the output voltage.
Input Capacitor Selection
The input capacitor (CIN) filters the current peaks drawn
from the input supply and reduces noise injection into
the ICs. A 4.7FF ceramic capacitor is used in the Typical
Operating Circuit (Figure 1) because of the high source
18
impedance seen in typical lab setups. Actual applications usually have much lower source impedance since
the step-up regulator often runs directly from the output
of another regulated supply. In some applications, CIN
can be reduced below the values used in the Typical
Operating Circuit. Ensure a low-noise supply at IN by
using adequate CIN, especially when running at low IN
voltage. Alternatively, greater voltage variation can be
tolerated on CIN if IN is decoupled from CIN using an RC
lowpass filter.
LED Selection and Bias
The series/parallel configuration of the LED load and the
full-scale bias current has a significant effect or regulator performance. LED characteristics vary significantly
from manufacturer to manufacturer. Consult the respective LED data sheets to determine the range of output
voltages for a given brightness and LED current. In
general, brightness increases as a function of bias current. This suggests that the number of LEDs could be
decreased if higher bias current is chosen; however, a
high current increases LED temperature and reduces
operating life. Improvements in LED technology are
resulting in devices with lower forward voltage while
increasing the bias current and light output.
LED manufacturers specify the LED color at a given LED
current. With lower LED current, the color of the emitted
light tends to shift toward the blue range of the spectrum.
A blue bias is often acceptable for business applications
but not for high-image-quality applications such as DVD
players. DPWM dimming is a viable solution for reducing
power dissipation while maintaining LED color integrity.
Careful attention should be paid to switching noise to
avoid other display quality problems.
Using fewer LEDs in a string improves step-up converter
efficiency, and lowers breakdown voltage requirements
of the external MOSFET and diode. The minimum number of LEDs in series should always be greater than maximum input voltage. If the diode voltage drop is lower
than maximum input voltage, the voltage drop across the
current-sense inputs (FB_) increases and causes excess
heating in the IC. Between 8 and 12 LEDs in series are
ideal for input voltages up to 20V.
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
LED VFB_ Variation
The forward voltage of each white LED may vary up to
25% from part to part and the accumulated voltage difference in each string equates to additional power loss
within the devices. For the best efficiency, the voltage
difference between strings should be minimized. The
difference between lowest voltage string and highest
voltage string should be less than 8V (typ). Otherwise,
the internal LED short-protection circuit disables the high
FB voltage string.
FB Pin Maximum Voltage
The current through each FB_ pin is controlled only during
the step-up converter’s on-time. During the converter offtime the current sources are turned off. The output voltage
does not discharge and stays high. The devices disable
the FB current source, which string shorts. In this case,
the step-up converter’s output voltage is always applied
to the disabled FB pin. FB_ pin can withstand 48V.
PCB Layout Guidelines
Careful PCB layout is important for proper operation. Use
the following guidelines for good PCB layout:
1) M
inimize the area of high current-switching loop
of the rectifier diode, internal MOSFET, and output
capacitor to avoid excessive switching noise.
2) C
onnect high-current input and output components
with short and wide connections. The high-current
input loop goes from the positive terminal of the input
capacitor to the inductor, to the internal MOSFET,
then to the input capacitor’s negative terminal. The
high-current output loop is from the positive terminal
of the input capacitor to the inductor, to the rectifier
diode, to the positive terminal of the output capacitors, reconnecting between the output capacitor and
input capacitor ground terminals. Avoid using vias
in the high-current paths. If vias are unavoidable,
use multiple vias in parallel to reduce resistance and
inductance.
3) C
reate a ground island (PGND) consisting of the
input and output capacitor ground. Connect all
these together with short, wide traces or a small
ground plane. Maximizing the width of the power
ground traces improves efficiency and reduces output-voltage ripple and noise spikes. Create an analog
ground island (GND) consisting of ISET, IN, VCC connections, and the devices’ exposed backside pad.
Connect the GND and PGND islands by connecting
the GND pins directly to the exposed backside pad.
Make no other connections between these separate
ground planes.
4) P
lace the IN pin and VCC pin bypass capacitors as
close to the device as possible. The ground connection of the bypass capacitors should be connected
directly to the GND pins with a wide trace.
5) M
inimize the size of the LX node while keeping it wide
and short. If possible, avoid running the LX node from
one side of the PCB to the other. Use DC traces as
shield if necessary.
Refer to the MAX17129/MAX17149 evaluation kit for an
example of proper board layout.
19
MAX17129/MAX17149
Applications Information
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
MAX17129/MAX17149
Simplified Operating Circuit
FSEL
IN
LX
VCC
PGND
MAX17129
OVP
ISET
FB1
FB2
FB3
EN
FB4
FB5
BRT
FB6
GND
EP
Chip Information
PROCESS: BiCMOS
20
Package Information
For the latest package outline information and land pat­terns
(footprints), 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
NO.
LAND
PATTERN NO.
16 TQFN-EP
T1633+5
21-0136
90-0032
Low-Cost, 6-String WLED Drivers with
Quick-PWM Step-Up Converter
REVISION
NUMBER
REVISION
DATE
0
12/10
1
9/11
DESCRIPTION
Initial release
PAGES
CHANGED
—
1–6, 8, 9,
12–15, 17
Updated die specifications
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
© 2011
Maxim Integrated Products 21
Maxim is a registered trademark of Maxim Integrated Products, Inc.
MAX17129/MAX17149
Revision History