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19-4141; Rev 3; 1/10
2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense
General Description
The MAX16822A/MAX16822B 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 MAX16822A/MAX16822B operate from a +6.5V to +65V input-voltage range and can provide an output current up to 350mA, if operated up to a temperature of +125C, or up to 500mA, 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 MAX16822A allows 10% current ripple and the MAX16822B allows 30% current ripple. Both devices operate up to a switching frequency of 2MHz, thus allowing the use of small-sized components. The MAX16822A/MAX16822B 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. An additional feature includes thermal-shutdown protection that turns off the LX driver when the junction temperature exceeds +165C. The MAX16822A/MAX16822B operate over the -40C to +125C automotive temperature range and are available in an 8-pin SO package. o High-Efficiency Solution o 6.5V to 65V Input-Voltage Range o Output Current Up to 500mA o On-Board 65V, 0.85 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 an 8-Pin SO Package o -40C to +125C Operating Temperature Range
KIT ATION EVALU ILABLE AVA
Features
MAX16822A/MAX16822B
Ordering Information
PART MAX16822AASA+ MAX16822AASA/V+ TEMP RANGE -40C to +125C -40C to +125C PIN-PACKAGE 8 SO 8 SO
MAX16822BASA+ -40C to +125C 8 SO +Denotes a lead(Pb)-free/RoHS-compliant package. /V denotes an automotive qualified part.
Typical Application Circuit
D1
HB LEDs VIN RSENSE L1
C2
Applications
Architectural, Industrial, and Ambient Lighting Automotive RCL, DRL, and Fog Lights Heads-Up Displays Indicator and Emergency Lighting
4 C1 3 GND PGND 1 2 CS IN TEMP_I DIM LX LX 8 7 6 5 *OPTIONAL NTC* ON OFF
MAX16822A MAX16822B
Pin Configuration appears at end of data sheet.
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense MAX16822A/MAX16822B
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 7.4mW/C above +70C)...............588.2mW Junction-to-Ambient Thermal Resistance (JA) (Note 1) ...136C/W Pin-to-Pin ESD Ratings......................................................2.5kV Operating Temperature Range 350mA (max) Output Current ........................-40C to +125C 500mA (max) Output Current ........................-40C to +105C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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, see 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 from 4V until VLX < 0.5VIN VCS = VIN - 100mV, VIN falling from 6.5V until VLX > 0.5VIN Undervoltage-Lockout Hysteresis SENSE COMPARATOR MAX16822A, (VIN - VCS) rising from 140mV until VLX > 0.5VIN MAX16822B, VIN - VCS rising from 140mV until VLX > 0.5VIN MAX16822A, VIN - VCS falling from 260mV until VLX < 0.5VIN MAX16822B, VIN - VCS falling from 260mV until VLX < 0.5VIN 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 201 218 185 166 210 230 190 170 50 50 3.5 216 mV 236 198 mV 180 ns ns A 0.5 6.25 6.5 V 6 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
Sense Voltage Threshold High
VSNSHI
Sense Voltage Threshold Low
VSNSLO
Propagation Delay to Output High Propagation Delay to Output Low CS Input Current
tDPDH tDPDL ICSIN
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 INTERNAL MOSFET VIN = VDIM = 24V, VCS = 23.9V, ILX = 350mA VIN = VDIM = 6.0V, VCS = 5.9V, ILX = 350mA VDIM = 0V, VLX = 65V VIN - VCS = 100mV VCS - VIN = 100mV VDIM rising edge to VLX < 0.5VIN VDIM = VIN VDIM = 0V Temperature rising -3 165 10 200 15 0 2.8 0.6 0.85 1 1.7 2 10 A V V ns A A C C SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX16822A/MAX16822B
Drain-to-Source Resistance
RDSON
LX Leakage Current 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 Hsysteresis THERMAL FOLDBACK Thermal-Foldback Enable Threshold Voltage Thermal-Foldback Slope TEMP_I Output Bias Current
ILX_LEAK VIH VIL tDIM_ON
VTFBON_THR FBSLOPE ITEMP_I
VDIM = 5V VDIM = 5V
1.9
2.0 0.75
2.12
V 1/V
25
26.5
28
A
Typical Operating Characteristics
(VIN = VDIM = 48V, CVCC = 1F, RSENSE = 0.62, L = 220H (connected between IN and CS). Typical values are at TA = +25C, unless otherwise noted.)
EFFICIENCY vs. VIN
MAX16822A toc01
DUTY CYCLE vs. VIN
90 80 DUTY CYCLE (%) 70 60 50 40 30 20 10
1 LED 3 LEDs 7 LEDs 9 LEDs 5 LEDs 11 LEDs 13 LEDs 15 LEDs
MAX16822A toc02
FREQUENCY vs. VIN
90 80 FREQUENCY (kHz) 70 60 50 40 30 20 10 0
1 LED 3 LEDs 13 LEDs 11 LEDs 9 LEDs 7 LEDs 5 LEDs 15 LEDs
MAX16822A toc03
100 95 EFFICIENCY (%) 90 85
1 LED 7 LEDs 9 LEDs 5 LEDs 3 LEDs
11 LEDs13 LEDs 15 LEDs
100
100
80 75 70 5 15 25 35 VIN (V) 45 55 65
0 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 MAX16822A/MAX16822B
Typical Operating Characteristics (continued)
(VIN = VDIM = 48V, CVCC = 1F, RSENSE = 0.62, L = 220H (connected between IN and CS). Typical values are at TA = +25C, unless otherwise noted.)
NORMALIZED ILED vs. VIN
MAX16822A toc04
QUIESCENT CURRENT vs. VIN
450 QUIESCENT CURRENT (A) 400 350 300 250 200 150 100 50 VDIM = 0V 0 5 10 15 20 25 30 35 40 45 50 55 60 65 VIN (V)
MAX16822A toc05
PWM DIMMING AT 200Hz DUTY CYCLE (10%)
MAX16822A toc06
1.10
500
1.05 NORMALIZED ILED
5 LEDs 7 LEDs 9 LEDs11 LEDs13 LEDs 15 LEDs 3 LEDs
ILED 200mA/div 0 VDIM 5V/div 0 VIN = 48V 8 LEDs 1ms/div
1.00
1 LED
0.950
0.90 0 5 10 15 20 25 30 35 40 45 50 55 60 65 VIN (V)
0
PWM DIMMING AT 200Hz DUTY CYCLE (90%)
MAX16822A toc07
PWM DIMMING AT 20kHz DUTY CYCLE (90%)
MAX16822A toc08
ILED 200mA/div 0 VDIM 5V/div 0 VIN = 48V 8 LEDs 1ms/div 10s/div
ILED 200mA/div 0 VDIM 5V/div 0
LED CURRENT vs. VTEMP_I
450 400 LED CURRENT (mA) 350 ILED (A) 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) 0 0.1 VIN = 48V 0.3
MAX16822A toc09
ILED vs. TEMPERATURE
MAX16822A toc10
500
0.5
0.4
0.2
-40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
4
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2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense MAX16822A/MAX16822B
Typical Operating Characteristics (continued)
(VIN = VDIM = 48V, CVCC = 1F, RSENSE = 0.62, L = 220H (connected between IN and CS). Typical values are at TA = +25C, unless otherwise noted.)
LXRDSON vs. TEMPERATURE
VIN = 65V 0.9 0.8 0.7 0.6 0.5 0.4 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (C)
MAX16822A toc11
ITEMP_I vs. TEMPERATURE
29.5 29.0 28.5 ITEMP_ (A)
MAX16822A toc12
1.0
30.0
LXRDSON ()
VIN = 48V VIN = 6.5V
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)
Pin Description
PIN 1 2 3 4 5, 6 7 8 NAME CS IN GND PGND LX DIM TEMP_I 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 Input. Bypass with a 0.01F capacitor to GND if thermal foldback or analog dimming is used. See the Thermal Foldback section for more details.
Detailed Description
The MAX16822A/MAX16822B are step-down, constantcurrent, high-brightness LED (HB LED) drivers. These devices operate from a +6.5V to +65V input-voltage range. The maximum output current is 500mA, if the part is used at temperatures up to +105C, or 350mA, if it is used up to +125C. A high-side 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 MAX16822A/MAX16822B
IN
VCC REGULATOR
VCC _ANA
MAX16822A MAX16822B
ISET
LX VCC _ANA
CS
CURRENT-SENSE COMPARATOR
GATE DRIVER
0.85, 65V DMOS SWITCH
BANDGAP REFERENCE
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
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2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense
Undervoltage Lockout (UVLO)
The MAX16822A/MAX16822B include 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 equation below to calculate the value of this resistor:
R SENSE () = 1 (VSNSHI + VSNSLO )(V) ILED (A) 2
MAX16822A/MAX16822B
DIM Input
LED dimming is achieved by applying a PWM signal at DIM. A logic level below 0.6V at DIM forces the MAX16822A/MAX16822B's 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 MAX16822A/MAX16822B 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 V SNSLO is sense voltage threshold low (see the Electrical Characteristics table for values).
Current-Regulator Operation
The MAX16822A/MAX16822B 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 R SENSE VIN x V x L
Analog Dimming
The MAX16822A/MAX16822B offer an analog dimming feature that reduces the output current when the voltage at TEMP_I is below the internal 2V threshold voltage. The MAX16822A/MAX16822B 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 MAX16822A/MAX16822B reduce the LED current. Use the following formula to set the analog dimming current.
1 I TF (A) = ILED (A) x 1 - FB SLOPE x VTFB _ ON - V A D (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 MAX16822A/MAX16822B 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 R SENSE 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 MAX16822A/MAX16822B also include a thermalfoldback 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 MAX16822A/B Design Tool available at:www.maxim-ic.com/MAX16822software.
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2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense MAX16822A/MAX16822B
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.
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching losses and stable operation. Use a multilayer board whenever possible for better noise immunity. Minimize ground noise by connecting high-current ground returns, the input bypass-capacitor ground lead, and
the output-filter ground lead to a single point (star ground configuration). In normal operation, there are two power loops. One is formed when the internal MOSFET is on and the high current flows through IN, RSENSE, LED load, the inductor, the internal MOSFET, and GND. The other loop is formed when the internal MOSFET is off and the high-current circulates through RSENSE, LED load, the inductor, and the freewheeling diode. Minimize each loop area to reduce noise interaction. Place RSENSE as close as possible to CS and IN. For better noise immunity, a Kelvin connection between CS and RSENSE is strongly recommended.
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2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense
Pin Configuration
PROCESS: BiCMOS
TOP VIEW +
CS 1 IN 2 GND 3 8 7 TEMP_I DIM LX LX
MAX16822A/MAX16822B
Chip Information
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE S8-2 DOCUMENT NO. 21-0041
MAX16822A MAX16822B
6 5
PGND 4
SO
8 SO
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2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense MAX16822A/MAX16822B
Revision History
REVISION NUMBER 0 1 2 3 REVISION DATE 5/08 6/08 5/09 1/10 Initial release Updated Ordering Information table to release MAX16822B. Revised General Description, Features, Absolute Maximum Ratings, and Detailed Description. Added /V part number. DESCRIPTION PAGES CHANGED -- 1 1, 2, 5 1
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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