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19-4140; Rev 3; 2/10
KIT ATION EVALU ABLE AVAIL
2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense
General Description
The MAX16832A/MAX16832C step-down constant-current high-brightness LED (HB LED) drivers provide a cost-effective design solution for automotive interior/exterior lighting, architectural and ambient lighting, LED bulbs, and other LED illumination applications. The MAX16832A/MAX16832C operate from a +6.5V to +65V input voltage range and can provide an output current up to 700mA, if operated up to a temperature of +125C, or up to a 1A if operated up to a temperature of +105C. A high-side current-sense resistor adjusts the output current, and a dedicated pulse-width modulation (PWM) input enables pulsed LED dimming over a wide range of brightness levels. These devices are well suited for applications requiring a wide input voltage range. The high-side current sensing and an integrated current-setting circuitry minimize the number of external components while delivering an average output current with 3% accuracy. A hysteretic control method ensures excellent input supply rejection and fast response during load transients and PWM dimming. The MAX16832A allows 10% current ripple, and the MAX16832C allows 30% current ripple. Both devices operate up to a 2MHz switching frequency, thus allowing the use of small-sized components. The MAX16832A/MAX16832C offer an analog dimming feature that reduces the output current by applying an external DC voltage below the internal 2V threshold voltage from TEMP_I to GND. TEMP_I also sources 25A to a negative temperature coefficient (NTC) thermistor connected between TEMP_I and GND, thus providing an analog thermal-foldback feature that reduces the LED current when the temperature of the LED string exceeds a specified temperature point. Additional features include thermal-shutdown protection. The MAX16832A/MAX16832C operate over the -40C to +125C automotive temperature range and are available in a thermally enhanced 8-pin SO package. o High-Efficiency Solution o 6.5V to 65V Input Voltage Range o Output Current Up to 1A o On-Board 65V, 0.45 Power MOSFET o Hysteretic Control: Up to 2MHz Switching Frequency o 3% LED Current Accuracy o 200mV Current-Sense Reference o Resistor-Programmable Constant LED Current o Integrated High-Side Current Sense o Thermal-Foldback Protection/Linear Dimming o Thermal-Shutdown Protection o Available in a Thermally Enhanced 8-Pin SO Package o -40C to +125C Operating Temperature Range
Features
MAX16832A/MAX16832C
Ordering Information
PART MAX16832AASA+ MAX16832CASA+ TEMP RANGE -40C to +125C -40C to +125C PIN-PACKAGE 8 SO-EP* 8 SO-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad.
Typical Application Circuit
D1
HB LEDs VIN RSENSE L1
Applications
Architectural, Industrial, and Ambient Lighting Automotive RCL, DRL, and Fog Lights Heads-Up Displays Indicator and Emergency Lighting MR16 and MR111 LED Lights
C1 3 4 GND PGND 2 IN 1 CS TEMP_I DIM LX LX 8 7 6 5
C2
NTC*
ON OFF
MAX16832A MAX16832C
Pin Configuration appears at end of data sheet.
*OPTIONAL
________________________________________________________________ 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.
2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense MAX16832A/MAX16832C
ABSOLUTE MAXIMUM RATINGS
IN, CS, LX, DIM to GND .........................................-0.3V to +70V TEMP_I to GND .......................................................-0.3V to +6V PGND to GND ......................................................-0.3V to +0.3V CS to IN .................................................................-0.3V to +0.3V Maximum Current into Any Pin (except IN, LX, and PGND).............................................20mA Continuous Power Dissipation (TA = +70C) 8-Pin SO (derate 23.3mW/C above +70C)...........1860.5mW Junction-to-Ambient Thermal Resistance (JA) (Note 1) .....43C/W Operating Temperature Range 700mA (max) Output Current ........................-40C to +125C 1A (max) Output Current ...............................-40C to +105C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C Pin-to-Pin ESD Ratings......................................................2.5kV
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
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
(VIN = +24V, VDIM = VIN, TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Input Voltage Range Ground Current Supply Current UNDERVOLTAGE LOCKOUT (UVLO) VCS = VIN - 100mV, VIN rising until VLX < 0.5VIN VCS = VIN - 100mV, VIN falling until VLX > 0.5VIN 0.5 MAX16832A, VIN - VCS rising from 140mV until VLX > 0.5VIN, VDIM = 5V MAX16832C, VIN - VCS rising from 140mV until VLX > 0.5VIN, VDIM = 5V MAX16832A, VIN - VCS falling from 260mV until VLX < 0.5VIN , VDIM = 5V MAX16832C, VIN - VCS falling from 260mV until VLX < 0.5VIN, VDIM = 5V Falling edge of VIN - VCS from 140mV to 260mV to VLX > 0.5VIN Rising edge of VCS - VIN from 260mV to 140mV to VLX < 0.5VIN VIN - VCS = 200mV, VIN = VCS VIN = VDIM = 24V, VCS = 23.9V, ILX = 700mA VIN = VDIM = 6.0V, VCS = 5.9V, ILX = 700mA VDIM = 0V, VLX = 65V 6.25 6.5 V 6.0 V SYMBOL VIN No switching VDIM < 0.6V, VIN = 12V CONDITIONS MIN 6.5 1.5 350 TYP MAX 65 UNITS V mA A
Undervoltage Lockout
UVLO
Undervoltage-Lockout Hysteresis SENSE COMPARATOR 201 218 185 166
210 230 190 170 50 50
216 mV 236 198 mV 180 ns ns 3.5 A
Sense Voltage Threshold High
VSNSHI
Sense Voltage Threshold Low
VSNSLO
Propagation Delay to Output High Propagation Delay to Output Low CS Input Current INTERNAL MOSFET
tDPDH tDPDL ICSIN
0.45 1
0.9 2 10 A
Drain-to-Source Resistance
RDSON
LX Leakage Current
ILX_LEAK
2
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2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +24V, VDIM = VIN, TA = TJ = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER DIM INPUT DIM Input-Voltage High DIM Input-Voltage Low DIM Turn-On Time DIM Input Leakage High DIM Input Leakage Low THERMAL SHUTDOWN Thermal-Shutdown Threshold Thermal-Shutdown Threshold Hysteresis THERMAL FOLDBACK Thermal-Foldback Enable Threshold Voltage Thermal-Foldback Slope TEMP_I Output Bias Current VTFB_ON FBSLOPE ITEMP_I VDIM = 5V VDIM = 5V 25 1.9 2.0 0.75 26.5 28 2.12 V 1/V A Temperature rising +165 10
o
MAX16832A/MAX16832C
SYMBOL VIH VIL tDIM_ON
CONDITIONS VIN - VCS = 100mV VCS - VIN = 100mV VDIM rising edge to VLX < 0.5VIN VDIM = VIN VDIM = 0V
MIN 2.8
TYP
MAX
UNITS V
0.6 200 8 -3 -1.5 15 0
V ns A A C C
o
Typical Operating Characteristics
(VIN = VDIM = 48V, RSENSE = 0.3, L = 220H (connected between IN and CS). Typical values are at TA = +25C, unless otherwise noted.)
EFFICIENCY vs. INPUT VOLTAGE
MAX16832A toc01
DUTY CYCLE vs. INPUT VOLTAGE
90 80 DUTY CYCLE (%) 70 60 50 40 30 20 10
1 LED 3 LEDs 15 LEDs 13 LEDs 11 LEDs 9 LEDs 7 LEDs 5 LEDs
MAX16832A toc02
FREQUENCY vs. INPUT VOLTAGE
450 400 FREQUENCY (kHz) 350 300 250 200 150 100 50 0
16 LEDs 1 LED 3 LEDs 11 LEDs 9 LEDs 7 LEDs 5 LEDs 15 LEDs
MAX16832A toc03
100 95 EFFICIENCY (%) 90 85 80 75 70 5 15 25
9 LEDs 7 LEDs 5 LEDs 3 LEDs
11 LEDs 13 LEDs 15 LEDs
100
500
13 LEDs
1 LED
0 35 VIN (V) 45 55 65 5 15 25 35 VIN (V) 45 55 65
5
15
25
35 VIN (V)
45
55
65
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2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense MAX16832A/MAX16832C
Typical Operating Characteristics (continued)
((VIN = VDIM = 48V, RSENSE = 0.3, L = 220H (connected between IN and CS). Typical values are at TA = +25C, unless otherwise noted.)
NORMALIZED ILED CURRENT vs. INPUT VOLTAGE
MAX16832A toc04
QUIESCENT CURRENT vs. INPUT VOLTAGE
MAX16832A toc05
PWM DIMMING AT 200Hz (10% DUTY CYCLE)
MAX16832A toc06
1.05 1.04 NORMALIZED ILED CURRENT 1.03 1.02 1.01 1.00 0.99 0.98 0.97 0.96 0.95
500 450 QUIESCENT CURRENT (A) 400 350 300 250 200 150 100 50 0 VDIM = 0V
VIN = 48V 8 LEDs
ILED 200mA/div
13 LEDs 11 LEDs 15 LEDs 7 LEDs 9 LEDs 1 LED 3 LEDs 5 LEDs
0 VDIM 5V/div 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 VIN (V)
0 5 10 15 20 25 30 35 40 45 50 55 60 65 VIN (V)
1ms/div
PWM DIMMING AT 200Hz (90% DUTY CYCLE )
MAX16822A toc07
PWM DIMMING AT 20kHz (90% DUTY CYCLE)
MAX16832A toc08
ILED 200mA/div
ILED 200mA/div
0 VDIM 5V/div 0
0 VDIM 5V/div VIN = 48V 8 LEDs 10s/div 0
VIN = 48V 8 LEDs 1ms/div
LED CURRENT vs. VTEMP_I
800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 VTEMP_I (V)
MAX16832A toc09
ILED vs. TEMPERATURE
0.9 0.8 0.7 ILED (A) 0.6 0.5 0.4 0.3 0.2 0.1 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C) VIN = 48V
MAX16832A toc10
1.0
4
_______________________________________________________________________________________
LED CURRENT (mA)
2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense MAX16832A/MAX16832C
Typical Operating Characteristics (continued)
((VIN = VDIM = 48V, RSENSE = 0.3, L = 220H (connected between IN and CS). Typical values are at TA = +25C, unless otherwise noted.)
LXRDSON vs. TEMPERATURE
VIN = 65V 0.6 VIN = 48V LXRDSON () 0.5 0.4 VIN = 6.5V 0.3 0.2 0.1 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
MAX16832A toc11
ITEMP_I vs. TEMPERATURE
29.5 29.0 28.5 ITEMP_I (A) 28.0 27.5 27.0 26.5 26.0 25.5 25.0 VIN = 48V -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
MAX16832A toc12
0.7
30.0
Pin Description
PIN 1 2 3 4 5, 6 7 8 -- NAME CS IN GND PGND LX DIM TEMP_I EP FUNCTION Current-Sense Input. Connect a resistor between IN and CS to program the LED current. Positive Supply Voltage Input. Bypass with a 1F or higher value capacitor to GND. Ground Power Ground Switching Node Logic-Level Dimming Input. Drive DIM low to turn off the current regulator. Drive DIM high to enable the current regulator. Thermal Foldback Control and Linear Dimming Input. Bypass with a 0.01F capacitor to GND if thermal foldback or analog dimming is used. See the Thermal Foldback section. Exposed Pad. Connect EP to a large-area ground plane for effective power dissipation. Do not use as the IC ground connection.
Detailed Description
The MAX16832A/MAX16832C are step-down, constantcurrent, HB LED drivers. These devices operate from a +6.5V to +65V input voltage range. The maximum output is 1A, if the part is used at temperatures up to TA = 105C. or 700mA, if it is used up to TA = +125C. A highside current-sense resistor sets the output current and a
dedicated PWM dimming input enables pulsed LED dimming over a wide range of brightness levels. A high-side current-sensing scheme and an on-board current-setting circuitry minimize the number of external components while delivering LED current with 3% accuracy, using a 1% sense resistor. See Figure 1 for an internal block diagram.
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5
2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense MAX16832A/MAX16832C
IN
VCC REGULATOR
VCC _ANA
MAX16832A MAX16832C
ISET OPEN LED COMPARATOR VCC _ANA LX
CS
CURRENT-SENSE COMPARATOR
GATE DRIVER
0.45, 65V DMOS SWITCH
BANDGAP REF
1.23V
PWM DIMMING
UVLO COMPARATOR
DIM
DIM BUFFER VCC _ANA 25A
TEMP_I PGND THERMAL FOLDBACK COMPARATOR
VFTBON_THR 2V
GND
Figure 1. Internal Block Diagram
6
_______________________________________________________________________________________
2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense
Undervoltage Lockout (UVLO)
The MAX16832A/MAX16832C include a UVLO with 500mV hysteresis. The internal MOSFET turns off when VIN falls below 5.5V to 6.0V.
Applications Information
Selecting RSENSE to Set LED Current The LED current is programmed with a current-sense resistor connected between IN and CS. Use the following equation to calculate the value of this resistor:
RSENSE () = 1 (VSNSHI + VSNSLO )(V) ILED (A) 2
MAX16832A/MAX16832C
DIM Input
LED dimming is achieved by applying a PWM signal at DIM. A logic level below 0.6V at DIM forces the MAX16832A/MAX16832Cs' output low, thus turning off the LED current. To turn the LED current on, the logic level at DIM must be greater than 2.8V.
Thermal Shutdown
The MAX16832A/MAX16832C thermal-shutdown feature turns off the LX driver when the junction temperature exceeds +165C. The LX driver turns back on when the junction temperature drops 10C below the shutdown temperature threshold.
where VSNSHI is the sense voltage threshold high and VSNSLO is the sense voltage threshold low (see the Electrical Characteristics table for values).
Current-Regulator Operation
The MAX16832A/MAX16832C regulate the LED current using a comparator with hysteresis (see Figure 2). As the current through the inductor ramps up and the voltage across the sense resistor reaches the upper threshold, the internal MOSFET turns off. The internal MOSFET turns on again when the inductor current ramps down through the freewheeling diode until the voltage across the sense resistor equals the lower threshold. Use the following equation to determine the operating frequency: fSW = (VIN - nVLED ) x nVLED x RSENSE VIN x V x L
Analog Dimming
The MAX16832A/MAX16832C offer an analog-dimming feature that reduces the output current when the voltage at TEMP_I is below the internal 2V threshold voltage. The MAX16832A/MAX16832C achieve analog dimming by either an external DC voltage source connected between TEMP_I and ground or by a voltage on a resistor connected across TEMP_I and ground induced by an internal current source of 25A. When the voltage at TEMP_I is below the internal 2V threshold limit, the MAX16832A/MAX16832C reduce the LED current. Use the following formula to set the analog dimming current:
1 ITF (A) = ILED (A) x 1- FBSLOPE x VTFB _ ON - VAD (V) V
where n is the number of LEDs, VLED is the forward voltage drop of 1 LED, and V = (VSNSHI - VSNSLO).
(
)
Inductor Selection
The MAX16832A/MAX16832C operate up to a switching frequency of 2MHz. For space-sensitive applications, the high switching frequency allows the size of the inductor to be reduced. Use the following formula to calculate an approximate inductor value and use the closest standard value: L(approx.) = (VIN - nVLED ) x nVLED x RSENSE VIN x V x fSW
where VTFB_ON = 2V and FBSLOPE = 0.75 are obtained from the Electrical Characteristics table and VAD is the voltage at TEMP_I.
Thermal Foldback
The MAX16832A/MAX16832C include a thermal-foldback feature that reduces the output current when the temperature of the LED string exceeds a specified temperature point. These devices enter thermal-foldback mode when the voltage drop on the NTC thermistor, thermally attached to the LEDs and electrically connected between TEMP_I and ground, drops below the internal 2V threshold limit.
For component selection, use the MAX16832A/C Design Tool available at: www.maxim-ic.com/MAX16832software.
_______________________________________________________________________________________
7
2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense MAX16832A/MAX16832C
HYSTERETIC MODE
ILED
fSW
I AVG. LED CURRENT t
VDIM
t1
t2
t
Figure 2. Current-Regulator Operation
Freewheeling-Diode Selection
For stability and best efficiency, a low forward-voltage drop diode with fast reverse-recovery time and low capacitance is recommended. A Schottky diode is a good choice as long as its breakdown voltage is high enough to withstand the maximum operating voltage.
terminal, or through the MOSFET to ground and then to the input cap positive terminal. Without a proper PCB layout, these square-wave switching currents can create problems in a hysteretic LED driver. The current control depends solely on the voltage across RSENSE. Any noise pickup on this node induces erratic switching of the internal MOSFET (the IC will operate at a much higher frequency). To help prevent this, place RSENSE as close as possible to CS and IN and keep the sense traces short. It is especially important to keep the square-wave switching currents in the freewheeling diode away from RSENSE. To minimize interference, place the freewheeling diode on the opposite side of the IC as RSENSE and position the input capacitor near the diode so it can return the high frequency currents to ground. The layout in Figure 3 should be used as a guideline. The dashed line shows the path of the high frequency components that cause disruption in operation. For a good thermal design, the exposed pad on the IC should solder to a large pad with many vias to the backside ground plane.
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching losses and stable operation. In normal operation, there are two power loops. One is formed when the internal MOSFET is on and the high current flows from ground through the input cap, R SENSE , the LED load, the inductor, and the internal MOSFET back to ground. The second loop is formed when the internal MOSFET is off and the high current circulates from the input cap positive terminal through RSENSE, the LED load, the inductor, and the freewheeling diode and back to the input cap positive terminal. Note that the current through RSENSE, the LED load, and the inductor is basically DC with some triangular ripple (low noise). The high-noise, large signal, fast transition switching currents only flow through the freewheeling diode to the input cap positive
8
_______________________________________________________________________________________
2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense MAX16832A/MAX16832C
LED+
LED-
CFILTER RSENSE
1
L
GND LX CIN VIAS FOR THERMAL TRANSFER TO BACKSIDE GROUND PLANE D
VIN
tOFF AND tON CURRENT PATHS KEEP THIS LOOP TIGHT.
Figure 3. PCB Layout
Pin Configuration
PROCESS: BiCMOS
TOP VIEW +
CS 1 IN 2 GND 3 8 7 TEMP_I DIM LX LX
Chip Information
Package Information
For the latest package outline information, go to www.maxim-ic.com/packages. PACKAGE TYPE 8 SO-EP PACKAGE CODE S8E-12 DOCUMENT NO. 21-0111
MAX16832A MAX16832C
6 5
PGND 4
SO-EP
_______________________________________________________________________________________
9
2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense MAX16832A/MAX16832C
Revision History
REVISION NUMBER 0 1 2 3 REVISION DATE 5/08 9/08 5/09 2/10 Initial release Introduced the MAX16832C. Revised General Description, Features, Absolute Maximum Ratings, and Detailed Description Updated PCB Layout Guidelines and added Figure 3 DESCRIPTION PAGES CHANGED -- 1 1, 2, 5 8, 9
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.
10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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