19-4140; Rev 3; 2/10 KIT ATION EVALU E L B A AVAIL 2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense Features 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 +125°C, or up to a 1A if operated up to a temperature of +105°C. 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. o High-Efficiency Solution 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 25µA 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 -40°C to +125°C automotive temperature range and are available in a thermally enhanced 8-pin SO package. o Thermal-Foldback Protection/Linear Dimming o 6.5V to 65V Input Voltage Range o Output Current Up to 1A o On-Board 65V, 0.45Ω 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-Shutdown Protection o Available in a Thermally Enhanced 8-Pin SO Package o -40°C to +125°C Operating Temperature Range Ordering Information PART TEMP RANGE PIN-PACKAGE MAX16832AASA+ -40°C to +125°C 8 SO-EP* MAX16832CASA+ -40°C to +125°C 8 SO-EP* +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. Typical Application Circuit D1 HB LEDs VIN RSENSE L1 Applications C2 Architectural, Industrial, and Ambient Lighting Automotive RCL, DRL, and Fog Lights 1 CS TEMP_I 8 Heads-Up Displays 2 Indicator and Emergency Lighting MR16 and MR111 LED Lights C1 3 4 Pin Configuration appears at end of data sheet. IN GND PGND MAX16832A MAX16832C DIM LX LX 7 NTC* ON OFF 6 5 *OPTIONAL ________________________________________________________________ Maxim Integrated Products 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. 1 MAX16832A/MAX16832C General Description MAX16832A/MAX16832C 2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense 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 = +70°C) 8-Pin SO (derate 23.3mW/°C above +70°C)...........1860.5mW Junction-to-Ambient Thermal Resistance (θJA) (Note 1) .....43°C/W Operating Temperature Range 700mA (max) Output Current ........................-40°C to +125°C 1A (max) Output Current ...............................-40°C to +105°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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 = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL Input Voltage Range CONDITIONS VIN MIN TYP 6.5 MAX UNITS 65 V Ground Current No switching 1.5 mA Supply Current VDIM < 0.6V, VIN = 12V 350 µA VCS = VIN - 100mV, VIN rising until VLX < 0.5VIN 6.25 UNDERVOLTAGE LOCKOUT (UVLO) Undervoltage Lockout UVLO 6.5 V VCS = VIN - 100mV, VIN falling until VLX > 0.5VIN 6.0 Undervoltage-Lockout Hysteresis 0.5 V SENSE COMPARATOR Sense Voltage Threshold High Sense Voltage Threshold Low VSNSHI VSNSLO MAX16832A, VIN - VCS rising from 140mV until VLX > 0.5VIN, VDIM = 5V 201 210 216 MAX16832C, VIN - VCS rising from 140mV until VLX > 0.5VIN, VDIM = 5V 218 230 236 MAX16832A, VIN - VCS falling from 260mV until VLX < 0.5VIN , VDIM = 5V 185 190 198 MAX16832C, VIN - VCS falling from 260mV until VLX < 0.5VIN, VDIM = 5V 166 170 180 mV mV Propagation Delay to Output High tDPDH Falling edge of VIN - VCS from 140mV to 260mV to VLX > 0.5VIN 50 ns Propagation Delay to Output Low tDPDL Rising edge of VCS - VIN from 260mV to 140mV to VLX < 0.5VIN 50 ns CS Input Current ICSIN VIN - VCS = 200mV, VIN = VCS 3.5 µA INTERNAL MOSFET Drain-to-Source Resistance LX Leakage Current 2 RDSON ILX_LEAK VIN = VDIM = 24V, VCS = 23.9V, ILX = 700mA 0.45 VIN = VDIM = 6.0V, VCS = 5.9V, ILX = 700mA 1 0.9 Ω VDIM = 0V, VLX = 65V _______________________________________________________________________________________ 2 10 µA 2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense (VIN = +24V, VDIM = VIN, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DIM INPUT DIM Input-Voltage High VIH VIN - VCS = 100mV DIM Input-Voltage Low VIL VCS - VIN = 100mV DIM Turn-On Time tDIM_ON 2.8 V 0.6 VDIM rising edge to VLX < 0.5VIN DIM Input Leakage High VDIM = VIN DIM Input Leakage Low VDIM = 0V V 200 -3 ns 8 15 µA -1.5 0 µA THERMAL SHUTDOWN Thermal-Shutdown Threshold Temperature rising +165 o C 10 o C Thermal-Shutdown Threshold Hysteresis THERMAL FOLDBACK Thermal-Foldback Enable Threshold Voltage VTFB_ON VDIM = 5V Thermal-Foldback Slope FBSLOPE VDIM = 5V TEMP_I Output Bias Current 1.9 2.0 25 26.5 2.12 V 0.75 ITEMP_I 1/V 28 µA Typical Operating Characteristics (VIN = VDIM = 48V, RSENSE = 0.3Ω, L = 220µH (connected between IN and CS). Typical values are at TA = +25°C, unless otherwise noted.) 1 LED 80 13 LEDs 80 11 LEDs 70 9 LEDs 7 LEDs 60 5 LEDs 50 3 LEDs 40 30 75 70 5 15 25 35 VIN (V) 45 55 65 500 450 300 7 LEDs 5 LEDs 250 200 100 10 50 0 0 25 11 LEDs 9 LEDs 350 20 15 35 VIN (V) 45 55 65 15 LEDs 400 3 LEDs 150 1 LED 5 13 LEDs MAX16832A toc03 15 LEDs 90 FREQUENCY (kHz) 90 85 100 MAX16832A toc02 11 LEDs 13 LEDs 15 LEDs DUTY CYCLE (%) EFFICIENCY (%) 95 9 LEDs 7 LEDs 5 LEDs 3 LEDs MAX16832A toc01 100 FREQUENCY vs. INPUT VOLTAGE DUTY CYCLE vs. INPUT VOLTAGE EFFICIENCY vs. INPUT VOLTAGE 1 LED 16 LEDs 5 15 25 35 45 55 65 VIN (V) _______________________________________________________________________________________ 3 MAX16832A/MAX16832C ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) ((VIN = VDIM = 48V, RSENSE = 0.3Ω, L = 220µH (connected between IN and CS). Typical values are at TA = +25°C, unless otherwise noted.) 1.02 13 LEDs 11 LEDs 15 LEDs 7 LEDs 9 LEDs 1 LED 3 LEDs 5 LEDs 1.00 0.99 MAX16832A toc05 450 QUIESCENT CURRENT (μA) 1.03 MAX16832A toc06 500 MAX16832A toc04 NORMALIZED ILED CURRENT 1.04 1.01 PWM DIMMING AT 200Hz (10% DUTY CYCLE) QUIESCENT CURRENT vs. INPUT VOLTAGE NORMALIZED ILED CURRENT vs. INPUT VOLTAGE 1.05 0.98 400 VIN = 48V 8 LEDs 350 ILED 200mA/div 300 250 200 0 150 0.97 100 0.96 50 0.95 0 VDIM 5V/div 0 VDIM = 0V 0 5 10 15 20 25 30 35 40 45 50 55 60 65 0 5 10 15 20 25 30 35 40 45 50 55 60 65 VIN (V) VIN (V) PWM DIMMING AT 200Hz (90% DUTY CYCLE ) 1ms/div PWM DIMMING AT 20kHz (90% DUTY CYCLE) MAX16822A toc07 MAX16832A toc08 ILED 200mA/div ILED 200mA/div 0 0 VIN = 48V 8 LEDs VIN = 48V 8 LEDs 1ms/div 10μs/div LED CURRENT vs. VTEMP_I ILED vs. TEMPERATURE 0 MAX16832A toc10 1.0 MAX16832A toc09 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 VIN = 48V 0 0 0.4 0.8 1.2 1.6 VTEMP_I (V) 4 VDIM 5V/div VDIM 5V/div 0 ILED (A) LED CURRENT (mA) MAX16832A/MAX16832C 2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense 2.0 2.4 2.8 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) _______________________________________________________________________________________ 2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense ITEMP_I vs. TEMPERATURE LXRDSON vs. TEMPERATURE 0.6 29.5 29.0 28.5 0.5 0.4 VIN = 6.5V 0.3 ITEMP_I (μA) LXRDSON (Ω) VIN = 48V 30.0 MAX16832A toc12 VIN = 65V MAX16832A toc11 0.7 28.0 27.5 27.0 26.5 26.0 0.2 25.5 25.0 0.1 VIN = 48V -40 -25 -10 5 20 35 50 65 80 95 110 125 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) TEMPERATURE (°C) Pin Description PIN NAME 1 CS Current-Sense Input. Connect a resistor between IN and CS to program the LED current. 2 IN Positive Supply Voltage Input. Bypass with a 1µF or higher value capacitor to GND. 3 GND 4 PGND 5, 6 LX 7 DIM 8 TEMP_I — EP FUNCTION 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 0.01µF 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 = 105°C. or 700mA, if it is used up to TA = +125°C. 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. _______________________________________________________________________________________ 5 MAX16832A/MAX16832C Typical Operating Characteristics (continued) ((VIN = VDIM = 48V, RSENSE = 0.3Ω, L = 220µH (connected between IN and CS). Typical values are at TA = +25°C, unless otherwise noted.) MAX16832A/MAX16832C 2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense IN VCC REGULATOR MAX16832A MAX16832C VCC _ANA ISET OPEN LED COMPARATOR LX VCC _ANA CS CURRENT-SENSE COMPARATOR 0.45Ω, 65V DMOS SWITCH PWM DIMMING 1.23V BANDGAP REF GATE DRIVER UVLO COMPARATOR DIM DIM BUFFER VCC _ANA 25μA TEMP_I PGND VFTBON_THR 2V THERMAL FOLDBACK COMPARATOR GND Figure 1. Internal Block Diagram 6 _______________________________________________________________________________________ 2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense 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 +165°C. The LX driver turns back on when the junction temperature drops 10°C below the shutdown temperature threshold. 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 25µA. 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) × ⎢1− FBSLOPE ⎜ ⎟ × VTFB _ ON − VAD (V)⎥ ⎝ ⎠ V ⎣ ⎦ ( ) where VTFB_ON = 2V and FBSLOPE = 0.75 are obtained from the Electrical Characteristics table and VAD is the voltage at TEMP_I. 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 (Ω) = 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 ) × nVLED × RSENSE VIN × ΔV × L where n is the number of LEDs, VLED is the forward voltage drop of 1 LED, and ΔV = (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: 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. 1 (VSNSHI + VSNSLO )(V) ILED (A) 2 L(approx.) = (VIN − nVLED ) × nVLED × RSENSE VIN × ΔV × fSW For component selection, use the MAX16832A/C Design Tool available at: www.maxim-ic.com/MAX16832software. _______________________________________________________________________________________ 7 MAX16832A/MAX16832C Applications Information 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. MAX16832A/MAX16832C 2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense HYSTERETIC MODE fSW ILED ΔI AVG. LED CURRENT t VDIM t2 t1 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. 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 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. _______________________________________________________________________________________ 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 VIN D tOFF AND tON CURRENT PATHS KEEP THIS LOOP TIGHT. Figure 3. PCB Layout Pin Configuration Chip Information PROCESS: BiCMOS TOP VIEW + CS 1 8 IN 2 GND 3 MAX16832A MAX16832C PGND 4 Package Information TEMP_I For the latest package outline information, go to www.maxim-ic.com/packages. 7 DIM 6 LX PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 5 LX 8 SO-EP S8E-12 21-0111 SO-EP _______________________________________________________________________________________ 9 MAX16832A/MAX16832C 2MHz, High-Brightness LED Drivers with Integrated MOSFET and High-Side Current Sense Revision History REVISION NUMBER REVISION DATE 0 5/08 Initial release — 1 9/08 Introduced the MAX16832C. 1 2 5/09 Revised General Description, Features, Absolute Maximum Ratings, and Detailed Description 3 2/10 Updated PCB Layout Guidelines and added Figure 3 DESCRIPTION PAGES CHANGED 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 © 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.