19-4972; Rev 2; 4/11 TION KIT EVALUA BLE AVAILA Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller Features The MAX16838 is a dual-channel LED driver that integrates both the DC-DC switching boost regulator and two 150mA current sinks. A current-mode switching DC-DC controller provides the necessary voltage to both strings of HB LEDs. The MAX16838 accepts a wide 4.75V to 40V input voltage range and directly withstands automotive load-dump events. For a 5V Q10% input voltage, connect VIN to VCC. The wide input range allows powering HB LEDs for small-to-medium-sized LCD displays in automotive and display backlight applications. SIntegrated, 2-Channel, 20mA to 150mA Linear LED Current Sinks SBoost or SEPIC Power Topologies for Maximum Flexibility SAdaptive Voltage Optimization to Minimize Power Dissipation in Linear Current Sinks S4.75V to 40V or 5V ±10% Input Operating Voltage Range S5000:1 PWM Dimming at 200Hz SOpen-Drain Fault Indicator Output SLED Open/Short Detection and Protection SOutput Overvoltage and Overtemperature Protection SProgrammable LED Current Foldback at Lower Input Voltages S200kHz to 2MHz Resistor Programmable Switching Frequency with External Synchronization SCurrent-Mode Control Switching Stage with Internal Slope Compensation SEnable Input SThermally Enhanced, 20-Pin TQFN (4mm x 4mm) and 20-Pin TSSOP Packages An internal current-mode switching DC-DC controller supports the boost or SEPIC topologies and operates in an adjustable frequency range between 200kHz and 2MHz. The current-mode control provides fast response and simplifies loop compensation. The MAX16838 also features an adaptive output-voltage adjustment scheme that minimizes the power dissipation in the LED current sink paths. The MAX16838 can be combined with the MAX15054 to achieve a buck-boost LED driver with two integrated current sinks. The channel current is adjustable from 20mA to 150mA using an external resistor. The external resistor sets both channel currents to the same value. The device allows connecting both strings in parallel to achieve a maximum current of 300mA in a single channel. The MAX16838 also features pulsed dimming control with minimum pulse widths as low as 1Fs, on both channels through a logic input (DIM). The MAX16838 includes an output overvoltage protection, open LED, shorted LED detection and overtemperature protection. The device operates over the -40NC to +125NC automotive temperature range. The MAX16838 is available in the 20-pin TSSOP and 4mm x 4mm, 20-pin TQFN packages. Ordering Information PART TEMP RANGE PIN-PACKAGE MAX16838ATP+ -40NC to +125NC 20 TQFN-EP* MAX16838ATP/V+ -40NC to +125NC 20 TQFN-EP* MAX16838AUP+ -40NC to +125NC 20 TSSOP-EP* MAX16838AUP/V+ -40NC to +125NC 20 TSSOP-EP* +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. /V denotes an automotive qualified part. Simplified Schematic 4.75V TO 40V Applications L D CIN R2OV Automotive Display Backlights LCD Display Backlights IN Automotive Lighting Applications DRAIN EN OV R1OV NDRV CFB GATE VCC OUT1 DRV MAX16838 OUT2 COUT LED STRINGS RISET ISET FLT DIM CS RT COMP CCOMP RCOMP SGND PGND LEDGND RRT RCS Typical Operating Circuit and Pin Configurations appear 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. MAX16838 General Description MAX16838 Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller ABSOLUTE MAXIMUM RATINGS IN, OUT_, DRAIN to SGND....................................-0.3V to +45V EN to SGND................................................-0.3V to (VIN + 0.3V) PGND to SGND.....................................................-0.3V to +0.3V LEDGND to SGND................................................-0.3V to +0.3V DRV to PGND........... -0.3V to the lower of (VIN + 0.3V) and +6V GATE to PGND.........................................................-0.3V to +6V NDRV to PGND........................................-0.3V to (VDRV + 0.3V) VCC, FLT, DIM, CS, OV, CFB, to SGND..................-0.3V to +6V RT, COMP, ISET to SGND..........................-0.3V to (VCC + 0.3V) DRAIN and CS Continuous Current................................... Q2.5A OUT_ Continuous Current.................................................175mA VDRV Short-Circuit Duration ......................................Continuous Continuous Power Dissipation (TA = +70NC) 20-Pin TQFN (derate 25.6mW/NC above +70NC).............2051mW 20-Pin TSSOP (derate 26.5mW/NC above +70NC).......2122mW Operating Temperature Range......................... -40NC to +125NC Junction Temperature......................................................+150NC Storage Temperature Range............................. -65NC to +150NC 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. PACKAGE THERMAL CHARACTERISTICS (Note 1) 20 TQFN Juction-to-Ambient Thermal Resistance (BJA)........... +39NC/W Junction-to-Case Thermal Resistance (BJC)................ +6NC/W 20 TSSOP Junction-to-Ambient Thermal Resistance (BJA)...... +37.7NC/W Junction-to-Case Thermal Resistance (BJC)................ +2NC/W 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. ELECTRICAL CHARACTERISTICS (VIN = VEN = 12V, RRT = 12.2kI, RISET = 15kI, CVCC = 1FF, VCC = VDRV = VCFB, DRAIN, COMP, OUT_, FLT = unconnected, VOV = VCS = VLEDGND = VDIM = VPGND = VSGND = 0V, VGATE = VNDRV, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = 25NC.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN Input Voltage Range VIN Internal LDO on 4.75 Input Voltage Range VIN VIN = VCC 4.55 Quiescent Supply Current IQ VDIM = 5V ISH VEN = SGND (Note 3) UVLOIN VIN rising, VDIM = 5V Standby Supply Current Undervoltage Lockout TYP Undervoltage Lockout Hysteresis UNITS 40 V 5.5 V 5 mA 15.5 40 FA 4.3 4.55 V 3.1 4 MAX 177 mV DRV REGULATOR Output Voltage Dropout Voltage VDRV VCC (UVLO) Hysteresis 6.5V < VIN < 40V, 0.1mA < ILOAD < 3mA 4.75 VDO VIN = 4.75V, IOUT = 30mA (VIN - VDRV) Short-Circuit Current Limit VCC Undervoltage Lockout Threshold 5.75V < VIN < 10V, 0.1mA < ILOAD < 30mA DRV shorted to GND UVLOVCC VCC rising 5 5.25 V 0.11 0.5 V 97 3.4 4.0 123 2 _______________________________________________________________________________________ mA 4.4 V mV Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller (VIN = VEN = 12V, RRT = 12.2kI, RISET = 15kI, CVCC = 1FF, VCC = VDRV = VCFB, DRAIN, COMP, OUT_, FLT = unconnected, VOV = VCS = VLEDGND = VDIM = VPGND = VSGND = 0V, VGATE = VNDRV, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = 25NC.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS RT OSCILLATOR Switching Frequency Range Duty Cycle fSW DMAX 2000 kHz fSW = 200kHz 200 87 90 95 % fSW = 2000kHz 83 85 91 % +7.5 % 3.6 V Oscillator Frequency Accuracy fSW = 200kHz to 2MHz -7.5 Synchronization Logic-High VRT rising 1.8 Synchronization Logic-Low VRT falling Logic-Level Before SYNC Capacitor 3.1 Synchronization Pulse Width SYNC Frequency Range 2.5 V 3.8 50 ns 1.1 x fSW fSYNC V 1.5 x fSW Hz PWM COMPARATOR Leading-Edge Blanking Propagation Delay to NDRV 66 ns Including leading-edge blanking time 100 ns Voltage ramp added to CS 0.12 V SLOPE COMPENSATION Slope Compensation Peak Voltage per Cycle CS LIMIT COMPARATOR CS Threshold Voltage VCS_MAX CS Limit Comparator Propagation Delay to NDRV CS Input Current VCOMP = 3V 285 10mV overdrive (including leading-edge blanking time) ICS 0 P VCS P 0.35V 300 315 100 -1.3 mV ns +0.5 FA ERROR AMPLIFIER OUT_ Regulation Voltage Transconductance VDIM = 5V Gm No-Load Gain A 0.9 1 1.1 V 340 600 880 FS (Note 4) 50 ISINK VDIM = VOUT_ = 5V, VCOMP = 3V 400 800 FA ISOURCE VDIM = 5V, VOUT_ = VCOMP = 0V 400 800 FA ISINK = 100mA, VIN > 5.5V 1.5 4 I ISOURCE = 100mA, VIN > 5.5V 1.5 4 I Peak Sink Current VNDRV = 5V 0.8 A Peak Source Current VNDRV = 0V 0.8 A COMP Sink Current COMP Source Current dB MOSFET DRIVER NDRV On-Resistance POWER MOSFET Power Switch On-Resistance ISWITCH = 0.5A, VGS = 5V 0.15 0.35 I Switch Leakage Current VDRAIN = 40V, VGATE = 0V 0.003 1.2 FA Switch Gate Charge VDRAIN = 40V, VGS = 4.5V 3.1 nC _______________________________________________________________________________________ 3 MAX16838 ELECTRICAL CHARACTERISTICS (continued) MAX16838 Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller ELECTRICAL CHARACTERISTICS (continued) (VIN = VEN = 12V, RRT = 12.2kI, RISET = 15kI, CVCC = 1FF, VCC = VDRV = VCFB, DRAIN, COMP, OUT_, FLT = unconnected, VOV = VCS = VLEDGND = VDIM = VPGND = VSGND = 0V, VGATE = VNDRV, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = 25NC.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 150 mA Q2 % 0.3 0.5 V 97 100 103 mA 95 100 105 mA 18.7 20 21.3 mA 1 300 nA LED CURRENT SINKS OUT_ Current Range IOUT_ VDIM = 5V, VOUT_ = 1.0V LED Strings Current Matching IOUT_ = 100mA, RISET = 15kI Maximum Peak-to-Peak Boost Ripple 1% IOUT variation, IOUT = 100mA, RISET = 15kI IOUT_ = 100mA, RISET = 15kI TA = +25NC TA = -40NC to +125NC IOUT_ = 20mA, RISET TA = -40NC to +125NC = 75kI VDIM = 0V, VOUT_ = 40V Output Current Accuracy OUT_ Leakage Current 20 Current Foldback Threshold Voltage 1.23 CFB Input Bias Current 0 P VCFB P 1.3V -0.3 VEN rising 1.1 V +0.3 FA ENABLE COMPARATOR (EN) Enable Threshold Enable Threshold Hysteresis VENHI VEN_HYS Enable Input Current 1.24 1.34 71 VEN = 40V -500 +50 V mV +700 nA DIM LOGIC DIM Input Logic-High VIH DIM Input Logic-Low VIL Hysteresis DIM Input Current 2.1 VDIM_HYS IDIM V 0.8 110 VDIM = 5V or 0 -600 V mV +100 nA DIM to LED Turn-On Time VDIM rising edge to 90% of set current 50 290 1000 ns DIM to LED Turn-Off Time VDIM falling edge to 10% of set current 10 121 700 ns IOUT_ Rise Time tR Rise time measured from 10% to 90% 120 600 ns IOUT_ Fall Time tF Fall time measured from 90% to 10% 50 500 ns LED FAULT DETECTION LED Shorted Fault Indicator Threshold TA = +125NC LED String Shorted Shutoff Threshold TA = +125NC Shorted LED Detection FLAG Delay 3.1 3.55 6 6.8 4.2 7.7 6 4 _______________________________________________________________________________________ 5.5 4.85 9.5 8.6 V V Fs Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller (VIN = VEN = 12V, RRT = 12.2kI, RISET = 15kI, CVCC = 1FF, VCC = VDRV = VCFB, DRAIN, COMP, OUT_, FLT = unconnected, VOV = VCS = VLEDGND = VDIM = VPGND = VSGND = 0V, VGATE = VNDRV, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = 25NC.) (Note 2) PARAMETER SYMBOL FLT LOGIC Output-Voltage Low VOL Output Leakage Current CONDITIONS MIN TYP MAX VIN = 4.75V and ISINK = 5mA VFILT = 5.5V -300 VOV rising 1.19 0 P VOV P 1.3V -100 UNITS 0.4 V +300 nA 1.265 V OVERVOLTAGE PROTECTION OV Trip Threshold 1.23 OV Hysteresis 70 OV Input Bias Current mV +100 nA THERMAL SHUTDOWN Thermal Shutdown 165 oC Thermal Shutdown Hysteresis 15 oC Note 2: All devices are 100% tested at TA = +125NC. Limits over temperature are guaranteed by design, not production tested. Note 3: The shutdown current does not include currents in the OV and CFB resistive dividers. Note 4: Gain = DVCOMP/DVCS, 0.05V < VCS < 0.15V. Typical Operating Characteristics (VIN = VEN = 12V, RRT = 12.2kI, RISET = 15kI, CVCC = 1FF, VCC = VDRV = VCFB, VDRAIN = VCOMP = VOUT_, FLT = unconnected, VOV = VCS = VLEDGND = VDIM = VPGND = VSGND = 0V, VGATE = VNDRV, TA = +25NC, unless otherwise noted.) SWITCHING WAVEFORM AT 200Hz (50% DUTY CYCLE) IIN vs. SUPPLY VOLTAGE MAX16838 toc02 5.0 MAX16838 toc01 4.5 10V/div 0V 100mA/div ILED 0A 20V/div 0V VOUT 4.0 IIIN (mA) VLX TA = +125°C TA = +25°C 3.5 3.0 TA = -40°C 2.5 VIN = 12V 2.0 1ms/div 4 8 12 16 20 24 28 32 36 40 SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 5 MAX16838 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (VIN = VEN = 12V, RRT = 12.2kI, RISET = 15kI, CVCC = 1FF, VCC = VDRV = VCFB, VDRAIN = VCOMP = VOUT_, FLT = unconnected, VOV = VCS = VLEDGND = VDIM = VPGND = VSGND = 0V, VGATE = VNDRV, TA = +25NC, unless otherwise noted.) SWITCHING FREQUENCY vs. TEMPERATURE IIN vs. FREQUENCY 8 IIN (mA) 7 6 5 4 3 2 1 360 MAX16838 toc04 9 359 SWITCHING FREQUENCY (kHz) MAX16838 toc03 10 358 357 356 355 354 353 352 VIN = 12V 351 VIN = 12V 0 350 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 -40 -25 -10 5 20 35 50 65 80 95 110 125 FREQUENCY (MHz) TEMPERATURE (°C) VISET vs. ILED VISET vs. TEMPERATURE 1.222 1.220 VIN = 12V 1.230 1.230 VISET (V) 1.219 1.229 1.218 1.217 1.229 VIN = 12V VDIM = 0V 1.216 1.229 1.215 20 -40 -25 -10 5 20 35 50 65 80 95 110 125 80 100 120 VEN_TH vs. TEMPERATURE EN LEAKAGE CURRENT vs. TEMPERATURE MAX16838 toc07 VEN RISING VEN FALLING 1.15 140 300 250 EN LEAKAGE CURRENT (nA) 1.20 60 ILED (mA) 1.30 1.25 40 TEMPERATURE (°C) 200 160 MAX16838 toc08 VISET (V) 1.221 1.230 MAX16838 toc06 MAX16838 toc05 1.223 VEN_TH (V) MAX16838 Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller VEN = 40V 150 100 VEN = 12V 50 1.10 0 -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) 6 _______________________________________________________________________________________ Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller DRV LINE REGULATION DRV LOAD REGULATION 5.000 TA = +125°C 5.000 TA = +25°C 4.995 VDRV (V) 4.990 TA = +25°C 4.990 4.985 TA = -40°C 4.980 TA = -40°C 4.975 4.980 4.970 4.975 VIN = 12V 4.965 10 20 30 40 50 0 5 10 15 20 25 INPUT VOLTAGE (V) LOAD (mA) FREQUENCY vs. RRT LODIM MODE RESPONSE 30 MAX16838 toc12 2.5 VIN = 12V 2.0 MAX16838 toc11 0 10V/div VIN 0V 5V/div VDIM 1.5 0V 100mA/div 1.0 IOUT_ 0A 20V/div 0.5 VLED_ DIM ON-TIME < 5 x fSW 0V 0 0 4 8 20ms/div 12 16 20 24 28 32 36 40 RRT (kI) LED SWITCHING WITH DIM AT 200Hz (50% DUTY CYCLE) 10mA/div IOUT1 0A 100mA/div IOUT2 0A 5V/div 0V VDIM 2ms/div 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 VIN = 12V MAX16838 toc14 ILED vs. RISET MAX16838 toc13 ILED (mA) FREQUENCY(MHz) TA = +125°C 5.005 4.995 4.985 MAX16838 toc10 5.005 DRV VOLTAGE (V) 5.010 MAX16838 toc09 5.010 10 15 20 25 30 35 40 45 50 55 60 65 70 75 RISET (kI) _______________________________________________________________________________________ 7 MAX16838 Typical Operating Characteristics (continued) (VIN = VEN = 12V, RRT = 12.2kI, RISET = 15kI, CVCC = 1FF, VCC = VDRV = VCFB, VDRAIN = VCOMP = VOUT_, FLT = unconnected, VOV = VCS = VLEDGND = VDIM = VPGND = VSGND = 0V, VGATE = VNDRV, TA = +25NC, unless otherwise noted.) Typical Operating Characteristics (continued) (VIN = VEN = 12V, RRT = 12.2kI, RISET = 15kI, CVCC = 1FF, VCC = VDRV = VCFB, VDRAIN = VCOMP = VOUT_, FLT = unconnected, VOV = VCS = VLEDGND = VDIM = VPGND = VSGND = 0V, VGATE = VNDRV, TA = +25NC, unless otherwise noted.) VIN = 12V VEN = HIGH 45 40 VOUT = 40V MAX16838 toc16 55 50 VOUT = 12V 35 30 25 20 15 10 5 0 -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) OV LEAKAGE CURRENT vs. TEMPERATURE POWER MOSFET RDSON vs. TEMPERATURE VIN = 12V VEN = HIGH 1.0 0.5 0 -0.5 -1.0 0.50 0.45 MAX16838 toc18 MAX16838 toc17 2.0 1.5 60 OUT_ LEAKAGE CURRENT (nA) VIN = 12V VEN = HIGH VCOMP = 2V VDIM = LOW POWER MOSFET RDSON (I) 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 OUT_ LEAKAGE CURRENT vs. TEMPERATURE MAX16838 toc15 COMP LEAKAGE CURRENT (nA) COMP LEAKAGE CURRENT vs. TEMPERATURE OV LEAKAGE CURRENT (nA) MAX16838 Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller VIN = 12V 0.40 0.35 0.30 0.25 0.20 0.15 0.10 -1.5 0.05 0 -2.0 -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) 8 _______________________________________________________________________________________ Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller PIN NAME FUNCTION 4 NDRV Gate Drive for Switching MOSFET. Connect NDRV to GATE directly or through a resistor to control the rise and fall times of the gate drive. 2 5 DRV 5V Regulator Output. MOSFET gate-driver supply input. Bypass DRV to PGND with a minimum of 1FF ceramic capacitor. Place the capacitor as close as possible to DRV and PGND. 3 6 VCC Internal Circuitry Supply Voltage. Bypass VCC to SGND with a minimum of 0.1FF ceramic capacitor. Place the capacitor as close as possible to VCC and SGND. 4 7 IN Supply Input. Connect a 4.75V to 40V supply to IN. Bypass IN to PGND with a minimum of 1FF ceramic capacitor. For a 5V Q10% supply voltage, connect VIN to VCC. 5 8 EN Enable/Undervoltage Lockout (UVLO) Threshold Input. EN is a dual-function input. Connect EN to VIN through a resistor-divider to program the UVLO threshold. 6 9 SGND Signal Ground. SGND is the current return path connection for the low-noise analog signals. Connect SGND, LEDGND, and PGND at a single point. TQFN TSSOP 1 7 10 CFB Current Foldback Reference Input. Connect a resistor-divider between IN, CFB, and ground to set the current foldback threshold. When the voltage at CFB goes below 1.23V, the LED current starts reducing linearly. Connect to VCC to disable the current foldback feature. 8 11 OV Overvoltage Threshold Adjust Input. Connect a resistor-divider from the switching converter output to OV and SGND. The OV comparator reference is internally set to 1.23V. 9 12 ISET LED Current Adjust Input. Connect a resistor RISET from ISET to SGND to set the current through each LED string (ILED) according to the formula ILED = 1512V/RISET. 10 13 FLT Open-Drain, Active-Low Flag Output. FLT asserts when there is an open/short-LED condition at the output or when there is a thermal shutdown event. 11 14 OUT2 12 15 LEDGND 13 16 OUT1 14 17 RT Oscillator Timing Resistor Connection. Connect a timing resistor (RRT) from RT to SGND to program the switching frequency. Apply an AC-coupled external clock at RT to synchronize the switching frequency with an external clock source. 15 18 COMP Switching Converter Compensation Input. Connect an RC network from COMP to SGND (see the Feedback Compensation section). LED String Cathode Connection 2. OUT2 is the open-drain output of the linear current sink that controls the current through the LED string connected to OUT2. OUT2 sinks up to 150mA. LED Ground. LEDGND is the return path connection for the linear current sinks. Connect SGND, LEDGND, and PGND at a single point. LED String Cathode Connection 1. OUT1 is the open-drain output of the linear current sink that controls the current through the LED string connected to OUT1. OUT1 sinks up to 150mA. _______________________________________________________________________________________ 9 MAX16838 Pin Description MAX16838 Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller Pin Description (continued) PIN NAME FUNCTION TQFN TSSOP 16 19 DIM Digital PWM Dimming Input 17 20 CS Current-Sense Input. CS is the current-sense input for the switching regulator and is also connected to the source of the internal power MOSFET. Connect a sense resistor from CS to PGND to set the switching current limit. 18 1 DRAIN Internal Switching MOSFET Drain Output 19 2 GATE Internal Switching MOSFET Gate Input. Connect GATE to NDRV directly or through a resistor to control the rise and fall times of the gate drive. 20 3 PGND Power Ground. PGND is the high-switching current return path connection. Connect SGND, LEDGND, and PGND at a single point. — — EP Exposed Pad. EP is internally connected to SGND. Connect EP to a large-area contiguous ground plane for effective power dissipation. Connect EP to SGND. Do not use as the only ground connection. 10 ������������������������������������������������������������������������������������� Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller FLT DRAIN POK SHDN DRV DIM SHORT-LED DETECTOR FLAG LOGIC CS DRIVER GATE PWM LOGIC NDRV OPEN-LED DETECTOR PWM COMP PGND 1.8V COMP RT MINIMUM STRING VOLTAGE RT OSCILLATOR GM 120mV ARRAY = 2 0 ILIM 1 1 0.3V 0 SLOPE COMPENSATION CS OUT_ OV SOFTSTART DAC CS BLANKING LOGIC DIM DUTY TOO LOW 1.0V 1.17V OV COMPARATOR IN DIM UVLO DRV 5V LDO BANDGAP VBG VCC VCC 1 THERMAL SHUTDOWN UVLO POK IN EN 0 SHDN MAX16838 VBG VBG SGND LEDGND OV CFB ISET ______________________________________________________________________________________ 11 MAX16838 Simplified Functional Diagram MAX16838 Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller Detailed Description The MAX16838 high-efficiency, HB LED driver integrates all the necessary features to implement a highperformance backlight driver to power LEDs in small-tomedium-sized displays for automotive as well as general applications. The device provides load-dump voltage protection up to 40V in automotive applications. The MAX16838 incorporates a DC-DC controller with peak current-mode control to implement a boost, coupled inductor boost-buck, or SEPIC-type switched-mode power supply and a 2-channel LED driver with 20mA to 150mA constant-current-sink capability per channel. The MAX16838 can be combined with the MAX15054 to achieve boost-buck topology without a coupled inductor (see Figure 5). The MAX16838 features a constant-frequency peak current-mode control with internal slope compensation to control the duty cycle of the PWM controller. The DC-DC converter generates the required supply voltage for the LED strings from a wide input supply range. Connect LED strings from the DC-DC converter output to the 2-channel constant current sinks that control the current through the LED strings. A single resistor connected from ISET to ground sets the forward current through both LED strings. The MAX16838 features adaptive LED voltage control that adjusts the converter output voltage depending on the forward voltage of the LED strings. This feature minimizes the voltage drops across the constant-current sinks and reduces power dissipation in the device. The MAX16838 provides a very wide PWM dimming range where a dimming pulse as narrow as 1Fs is possible at a 200Hz dimming frequency. A logic input (EN) shuts down the device when pulled low. The device includes an internal 5V LDO to power up the internal circuitry and drive the internal switching MOSFET. The MAX16838 includes output overvoltage protection that limits the converter output voltage to the programmed OV threshold in the event of an open-LED condition. The device also features an overtemperature protection that shuts down the controller if the die temperature exceeds +165°C. In addition, the MAX16838 has a shorted LED string detection and an open-drain FLT signal to indicate open LED, shorted LED, and overtemperature conditions. Current-Mode DC-DC Controller The MAX16838 uses current-mode control to provide the required supply voltage for the LED strings. The internal MOSFET is turned on at the beginning of every switching cycle. The inductor current ramps up linearly until it is turned off at the peak current level set by the feedback loop. The peak inductor current is sensedfrom the voltage across the current-sense resistor (RCS) connected from the source of the internal MOSFET to PGND. A PWM comparator compares the current-sense voltage plus the internal slope compensation signal with the output of the transconductance error amplifier. The controller turns off the internal MOSFET when the voltage at CS exceeds the error amplifier’s output voltage. This process repeats every switching cycle to achieve peak current-mode control. Error Amplifier The internal error amplifier compares an internal feedback (FB) signal with an internal reference voltage (VREF) and regulates its output to adjust the inductor current. An internal minimum string detector measures the minimum LED string cathode voltage with respect to SGND. During normal operation, this minimum VOUT_ voltage is regulated to 1V through feedback. The resulting DC-DC converter output voltage is 1V above the maximum required total LED voltage. The converter stops switching when LED strings are turned off during PWM dimming. The error amplifier is disconnected from the COMP output to retain the compensation capacitor charge. This allows the converter to settle to a steady-state level immediately when the LED strings are turned on again. This unique feature provides fast dimming response without having to use large output capacitors. If the PWM dimming on-pulse is less than five switching cycles, the feedback controls the voltage on OV such that the converter output voltage is regulated at 95% of the OV threshold. This mode ensures that narrow PWM dimming pulses are not affected by the response time of the converter. During this mode, the error amplifier remains continuously connected to the COMP output. Adaptive LED Voltage Control The MAX16838 reduces power dissipation using an adaptive LED voltage control scheme. The adaptive LED voltage control regulates the DC-DC converter output based on the operating voltage of the LED strings. 12 ������������������������������������������������������������������������������������� Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller Current Limit The MAX16838 includes a fast current-limit comparator to terminate the on-cycle during an overload or a fault condition. The current-sense resistor (RCS) connected between the source of the internal MOSFET and ground sets the current limit. The CS input has a 0.3V voltage trip level (VCS). Use the following equation to calculate RCS: as the oscillator frequency. The oscillator frequency is determined using the following formula: fSW = (7.342X109/RRT)(Hz) where RRT is in ω. Synchronize the oscillator with an external clock by AC-coupling the external clock to the RRT input. The capacitor used for the AC-coupling should satisfy the following relation: 9.862 CSYNC ≤ − 0.144 × 10−3 (µF) R T where RRT is in I. The pulse width for the synchronization signal should satisfy the following relations: tPW VS < 0.8 tCLK RCS = (VCS)/IPEAK tPW VS + VS > 3.4 0.8 − tCLK where IPEAK is the peak current that flows through the MOSFET. Undervoltage Lockout The MAX16838 features two undervoltage lockouts: UVLOIN and UVLOVCC. The undervoltage lockout threshold for VIN is 4.3V (typ) and the undervoltage lockout threshold for VCC is 4V (typ). Soft-Start The MAX16838 features a soft-start that activates during power-up. The soft-start ramps up the output of the converter in 64 steps in a period of 100ms (typ), unless both strings reach regulation point, in which case the soft-start would terminate to resume normal operation immediately. Once the soft-start is over, the internal soft-start circuitry is disabled and the normal operation begins. Oscillator Frequency/External Synchronization The MAX16838 oscillator frequency is programmable between 200kHz and 2MHz using one external resistor (RRT) connected between RT and SGND. The PWM MOSFET driver output switching frequency is the same where tPW is the synchronization source pulse width, tCLK is the synchronization clock time period, and VS is the synchronization pulse voltage level. See Figure 1. 5V LDO Regulator (DRV) The internal LDO regulator converts the input voltage at IN to a 5V output voltage at DRV. The LDO regulator output supports up to 30mA current, enough to provide power to the internal control circuitry and the gate driver. VS tPW tCLK Figure 1. Synchronizing External Clock Signal ______________________________________________________________________________________ 13 MAX16838 The voltage at each of the current-sink outputs (OUT_) is the difference between the DC-DC regulator output voltage (VLED) and the total forward voltage of the LED string connected to the output (OUT_). The DC-DC converter then adjusts VLED until the output channel with the lowest voltage at OUT_ is 1V relative to LEDGND. As a result, the device minimizes power dissipation in the current sinks and still maintains LED current regulation. For efficient adaptive control functionality, use an equal number of HB LEDs of the same forward voltage rating in each string. MAX16838 Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller Connect a 4.7I resistor from VCC to DRV to power the rest of the chip from the VCC pin with the 5V internal regulator. Bypass DRV to PGND with a minimum of 1FF ceramic capacitor as close as possible to the device. For input voltage range of 4.5V to 5.5V, connect IN to VCC. LED Current Control (ISET) The MAX16838 features two identical constant-current sources used to drive multiple HB LED strings. The current through each of the channels is adjustable between 20mA and 150mA using an external resistor (RISET) connected between ISET and SGND. Select RISET using the following formula: RISET = 1512 IOUT _ (Ω) where IOUT_ is the desired output current for both channels in amps. For single-channel operation, connect channel 1 and channel 2 together. See Figure 2. LED Dimming Control The MAX16838 features LED brightness control using an external PWM signal applied at DIM. The device accepts a minimum pulse width of 1Fs. Therefore, a 5000:1 dimming ratio is achieved when using a PWM frequency of 200Hz. Drive DIM high to enable both LED current sinks and drive DIM low to disable both LED current sinks. BOOST CONVERTER OUTPUT Fault Protections The MAX16838 fault protections include cycle-by-cycle current limiting, DC-DC converter output overvoltage protection, open-LED detection, short-LED detection, and overtemperature detection. An open-drain LED fault flag output (FLT) goes low when an open-LED/short-LED or overtemperature condition is detected. Open-LED Management and Overvoltage Protection The MAX16838 monitors the drains of the current sinks (OUT_) to detect any open string. If the voltage at any output falls below 300mV and the OV threshold is triggered (i.e., even with OUT_ at the OV voltage the string is not able to regulate above 300mV), then the MAX16838 interprets that string to be open, asserts FLT, and disconnects that string from the operation loop. The MAX16838 features an adjustable overvoltage threshold input (OV). Connect a resistor-divider from the switching converter output to OV and SGND to set the overvoltage threshold level. Use the following formula to program the overvoltage threshold: R2 VOV = 1.23V × 1 + OV R1OV 40mA TO 300mA OUT1 MAX16838 The duty cycle of the PWM signal applied to DIM also controls the DC-DC converter’s output voltage. If the turn-on duration of the PWM signal is less than five oscillator clock cycles, then the boost converter regulates its output based on feedback from the OV input. During this mode, the converter output voltage is regulated to 95% of the OV threshold voltage. If the turn-on duration of the PWM signal is greater than or equal to six oscillator clock cycles, then the converter regulates its output such that the minimum voltage at OUT_ is 1V. OUT2 Figure 2. Configuration for Higher LED String Current Short-LED Detection The MAX16838 features a two-level short-LED detection circuitry. If a level 1 short is detected on any one of the strings, FLT is asserted. A level 1 short is detected if the difference between the total forward LED voltages of the two strings exceeds 4.2V (typ). If a level 2 short is detected on any one of the strings, the particular LED string with the short is turned off after 6Fs and FLT is asserted. A level 2 short is detected if the difference between the total forward LED voltages of the two strings exceeds 7.8V (typ). The strings are reevaluated on each DIM rising edge and FLT is deasserted if the short is removed. 14 ������������������������������������������������������������������������������������� Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller VON R1EN = − 1 × R2EN V UVLOIN where VUVLOIN is the EN rising threshold (1.24V) and VON is the desired input startup voltage. Choose an R2EN between 10kI and 50kI. Connect EN to IN if not used. VIN MAX16838 R1EN EN R2EN 1.24V Figure 3. Setting the MAX16838 Undervoltage Lockout Threshold Inductor Selection in Boost Configuration Select the maximum peak-to-peak ripple on the inductor current (ILP-P). Use the following equations to calculate the maximum average inductor current (ILAVG) and peak inductor current (ILPEAK): ILAVG = ILED/(1 - DMAX) Current Foldback The MAX16838 includes a current-foldback feature to limit the input current at low VIN. Connect a resistordivider between IN, CFB, and SGND to set the currentfoldback threshold. When the voltage at CFB goes below 1.23V, then the LED current starts reducing proportionally to VCFB. Assuming ILP-P is 40% of the average inductor current: This feature can also be used for analog dimming of the LEDs. Connect CFB to VCC to disable this feature. Choose an inductor that has a minimum inductance greater than the calculated LMIN and current rating greater than ILPEAK. The recommended saturation current limit of the selected inductor is 10% higher than the inductor peak current. The ILP-P can be chosen to have a higher ripple than 40%. Adjust the minimum value of the inductance according to the chosen ripple. One fact that must be noted is that the slope compensation is fixed and has a 120mV peak per switching cycle. The dv/dt of the slope compensation ramp is 120fSWV/ Fs, where fSW is in kHz. After selecting the inductance it is necessary to verify that the slope compensation is adequate to prevent subharmonic oscillations. In the case of the boost, the following criteria must be satisfied: Applications Information Boost-Circuit Design First, determine the required input supply voltage range, the maximum voltage needed to drive the LED strings including the minimum 1V across the constant LED current sink (VLED), and the total output current needed to drive the LED strings (ILED). Calculate the maximum duty cycle (DMAX) using the following equation: DMAX = (VLED + VD – VIN_MIN)/(VLED + VD) where VD is the forward drop of the rectifier diode, VIN_MIN is the minimum input supply voltage, and VLED is the output voltage. Select the switching frequency (fSW) depending on the space, noise, dynamic response, and efficiency constraints. ILP-P = ILAVG x 0.4 ILPEAK = ILAVG + ILP-P/2 Calculate the minimum inductance value LMIN with the inductor current ripple set to the maximum value: LMIN = VIN_MIN x DMAX/(fSW x ILP-P) 120fSW > RCS (VLED - 2VIN_MIN)/2L where L is the inductance value in FH, RCS is the current-sense resistor value in ω, VIN_MIN is the minimum input voltage in V, VLED is the output voltage, and fSW is the switching frequency in kHz. If the inductance value is chosen to keep the inductor in discontinuous conduction mode, the equation above does not need to be satisfied. ______________________________________________________________________________________ 15 MAX16838 Enable (EN) EN is a logic input that completely shuts down the device when connected to logic-low, reducing the current consumption of the device to less than 15FA (typ). The logic threshold at EN is 1.24V (typ). The voltage at EN must exceed 1.24V before any operation can commence. There is a 71mV hysteresis on EN. The EN input also allows programming the supply input UVLO threshold using an external voltage-divider to sense the input voltage, as shown in Figure 3. Use the following equation to calculate the value of R1EN and R2EN in Figure 3: MAX16838 Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller Output Capacitor Selection in Boost Configuration For the boost converter, the output capacitor supplies the load current when the main switch is on. The required output capacitance is high, especially at higher duty cycles. Calculate the output capacitor (COUT) using the following equation: COUT > (DMAX x ILED)/(VLED_P-P x fSW) where VLED_P-P is the peak-to-peak ripple in the LED supply voltage. Use a combination of low-ESR and highcapacitance ceramic capacitors for lower output ripple and noise. Input Capacitor Selection in Boost Configuration The input current for the boost converter is continuous and the RMS ripple current at the input capacitor is low. Calculate the minimum input capacitor CIN using the following equation: CIN = ILP-P/(8 x fSW x VIN_P-P) where VIN_P-P is the peak-to-peak input ripple voltage. This equation assumes that input capacitors supply most of the input ripple current. Rectifier Diode Selection Using a Schottky rectifier diode produces less forward drop and puts the least burden on the MOSFET during reverse recovery. A diode with considerable reverse-recovery time increases the MOSFET switching loss. Select a Schottky diode with a voltage rating 20% higher than the maximum boost-converter output voltage and current rating greater than that calculated in the following equation: IL AVG ID = 1.2 × 1- D MAX (A) Feedback Compensation The voltage feedback loop needs proper compensation for stable operation. This is done by connecting a resistor (RCOMP) and capacitor (CCOMP) in series from COMP to SGND. RCOMP is chosen to set the highfrequency integrator gain for fast transient response, while CCOMP is chosen to set the integrator zero to maintain loop stability. For optimum performance, choose the components using the following equations: RCOMP = fZRHP × RCS × ILED 5 × FP1× GMCOMP × VLED × (1 − DMAX ) where fZRHP = VLED (1 − DMAX )2 2π × L × ILED is the right-half plane zero for the boost regulator. RCS is the current-sense resistor in series with the source of the internal switching MOSFET. ILED is the total LED current that is the sum of the LED currents in both the channels. VLED is the output voltage of the boost regulator. DMAX is the maximum duty cycle that occurs at minimum input voltage. GMCOMP is the transconductance of the error amplifier. FP1 = ILED 2 × π × VLED × COUT is the output pole formed by the boost regulator. Set the zero formed by RCOMP and CCOMP a decade below the crossover frequency. Using the value of RCOMP from above, the crossover frequency is at fZRHP/5. 50 CCOMP = 2π × RCOMP × fZRHP 16 ������������������������������������������������������������������������������������� Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller L1 Cs D CIN COUT L2 R2OV LED STRINGS R1OV R2EN IN EN R1EN CVCC DRAIN OV NDRV CFB GATE VCC OUT1 OUT2 RDRV RISET MAX16838 DRV ISET CDRV FLT RCOMP CCOMP DIM CS COMP RT SGND PGND LEDGND RRT RCS Figure 4. SEPIC Configuration SEPIC Operation Figure 4 shows a SEPIC application circuit using the MAX16838. The SEPIC topology is necessary to keep the output voltage of the DC-DC converter regulated when the input voltage can rise above and drop below the output voltage. Boost-Buck Configuration Figure 5 shows a boost-buck configuration with the MAX16838 and MAX15054. PCB Layout Considerations LED driver circuits based on the MAX16838 device use a high-frequency switching converter to generate the voltage for LED strings. Take proper care while laying out the circuit to ensure proper operation. The switchingconverter part of the circuit has nodes with very fast voltage changes that could lead to undesirable effects on the sensitive parts of the circuit. Follow these guidelines to reduce noise as much as possible: 1) Connect the bypass capacitor on VCC and DRV as close as possible to the device, and connect the capacitor ground to the analog ground plane using vias close to the capacitor terminal. Connect SGND of the device to the analog ground plane using a via close to SGND. Lay the analog ground plane on the inner layer, preferably next to the top layer. Use the analog ground plane to cover the entire area under critical signal components for the power converter. 2) Have a power ground plane for the switchingconverter power circuit under the power components (input filter capacitor, output filter capacitor, inductor, MOSFET, rectifier diode, and currentsense resistor). Connect PGND to the power ground plane as close to PGND as possible. Connect all other ground connections to the power ground plane using vias close to the terminals. ______________________________________________________________________________________ 17 MAX16838 4.75V TO 40V MAX16838 Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller 3) There are two loops in the power circuit that carry high-frequency switching currents. One loop is when the MOSFET is on—from the input filter capacitor positive terminal, through the inductor, the internal MOSFET, and the current-sense resistor, to the input capacitor negative terminal. The other loop is when the MOSFET is off—from the input capacitor positive terminal, through the inductor, the rectifier diode, output filter capacitor, to the input capacitor negative terminal. Analyze these two loops and make the loop areas as small as possible. Wherever possible, have a return path on the power ground plane for the switching currents on the top layer copper traces, or through power components. This reduces the loop area considerably and provides a low-inductance path for the switching currents. Reducing the loop area also reduces radiation during switching. 4) Connect the power ground plane for the constantcurrent LED driver part of the circuit to LEDGND as close as possible to the device. Connect SGND to PGND at the same point. D1 VDD VIN BST C1 MAX15054 GND CBST Q1 HDRV HI LX L D3 D2 COUT R1OV CIN LED STRINGS R1EN IN GATE NDRV R2EN CVCC R2OV DRAIN EN CFB OV VCC OUT1 OUT2 RDRV RISET MAX16838 DRV ISET CDRV FLT CS RT DIM COMP RCOMP SGND PGND LEDGND RRT RCS CCOMP Figure 5. Boost-Buck Configuration 18 ������������������������������������������������������������������������������������� Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller PGND GATE DRAIN CS DIM TOP VIEW 20 19 18 17 16 + + DRAIN 1 20 CS GATE 2 19 DIM PGND 3 18 COMP NDRV 1 15 COMP DRV 2 14 RT VCC 3 13 OUT1 DRV 5 16 OUT1 IN 4 12 LEDGND VCC 6 15 LEDGND 5 11 *EP 9 OUT2 MAX16838 17 RT IN 7 14 OUT2 EN 8 13 FLT SGND 9 10 12 ISET CFB 10 FLT 8 ISET 7 OV SGND 6 CFB EN MAX16838 NDRV 4 *EP 11 OV TSSOP TQFN *EXPOSED PAD Typical Operating Circuit 4.75V TO 40V L D CIN R2OV COUT LED STRINGS R1OV R2EN IN R1EN DRAIN OV EN NDRV CFB GATE VCC CVCC OUT1 OUT2 RDRV RISET MAX16838 DRV ISET CDRV FLT RCOMP CCOMP DIM CS COMP RT SGND PGND LEDGND RRT RCS ______________________________________________________________________________________ 19 MAX16838 Pin Configurations MAX16838 Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller Package Information Chip Information PROCESS: BiCMOS DMOS 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. 20 TQFN-EP T2044+3 21-0139 90-0037 20 TSSOP-EP U20E+1 21-0108 90-0114 20 ������������������������������������������������������������������������������������� Integrated, 2-Channel, High-Brightness LED Driver with High-Voltage Boost and SEPIC Controller REVISION NUMBER REVISION DATE 0 9/02 Initial release 1 12/09 Added /V part number, updated soldering temperature 2 4/11 Corrected formulas for CSYNC and OVP DESCRIPTION PAGES CHANGED — 1, 2 2, 13, 14 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. MAX16838 Revision History