EVALUATION KIT AVAILABLE MAX8790A Six-String White LED Driver with Active Current Balancing for LCD Panel Applications General Description Features The MAX8790A is a high-efficiency driver for white light- Drives Six Parallel Strings with Multiple Series- emitting diodes (LEDs). It is designed for large liquidcrys- Connected LEDs per String tal displays (LCDs) that employ an array of LEDs as the 1.5% Current Regulation Accuracy Between Strings light source. A current-mode step-up controller drives up Low 450mV Feedback Voltage at Full Current to six parallel strings of multiple series-connected LEDs. Improves Efficiency Each string is terminated with ballast that achieves 1.5% Step-Up Controller Regulates the Output Just Above current regulation accuracy, ensuring even brightness for the Highest LED String Voltage all LEDs. The MAX8790A has a wide input-voltage range from 4.5V to 26V, and provides a fixed 20mA or adjustable Full-Scale LED Current Adjustable from 15mA to 15mA to 27mA full-scale LED current. 27mA, or Preset 20mA Wide 100:1 Dimming Range The MAX8790A has two dimming control modes to enable a wide variety of applications. In direct DPWM mode, the Programmable Dimming Control: Direct DPWM or LED current is directly turned on and off by a PWM signal. Analog Dimming In analog dimming mode, an internal phase-locked loop Built-In PLL for Synchronized Dimming Control (PLL) circuit translates the PWM signal into an analog sig- Open and Short LED Protections nal and linearly controls the LED current down to 12.5%. Output Overvoltage Protection Below 12.5%, digital dimming is added to allow lower average LED current down to 1%. Both control methods Wide Input Voltage Range from 4.5V to 26V provide 100:1 dimming range. External MOSFET Allows a Large Number of LEDs The MAX8790A has multiple features to protect the con- per String troller from fault conditions. Separate feedback loops limit 500kHz/750kHz/1MHz Switching Frequency the output voltage if one or more LEDs fail open or short. Small, 20-Pin, 4mm x 4mm Thin QFN Package The controller features cycle-by-cycle current limit to pro- vide consistent operation and soft-start capability. A ther- Simplified Operating Circuit mal-shutdown circuit provides another level of protection. L1 D1 VOUT The step-up controller uses an external MOSFET, which VIN provides good efficiency and allows for scalable output C IN power and maximum operating voltage. Low feedback 0.1F voltage at each LED string (450mV) helps reduce power loss. The MAX8790A features selectable switching fre- IN SHDN EXT N1 quency (500kHz, 750kHz, or 1MHz), which allows trade-offs V CC CS FSET between external component size and ope-rating efficiency. ISET R The MAX8790A is available in a thermally enhanced, S MAX8790A lead-free, 20-pin, 4mm x 4mm, thin QFN package. GND BRT Applications R1 OV N.C. OSC Notebook, Subnotebook, and Tablet Computer Displays R2 N.C. CPLL Handy Terminals CCV FB1 FB2 Ordering Information FB3 ENA FB4 PART TEMP RANGE PIN-PACKAGE EP FB5 MAX8790AETP+ -40C to +85C 20 TQFN-EP* FB6 +Denotes a lead(Pb)-free/RoHS-compliant package. Pin Configuration appears at end of data sheet. *EP = Exposed pad. 19-0989 Rev 1 10/14MAX8790A Six-String White LED Driver with Active Current Balancing for LCD Panel Applications Absolute Maximum Ratings IN, SHDN, to GND..................................................-0.3V to +28V Operating Temperature Range.............................-40C to +85C FB to GND............................................................-0.3V to +28V Junction Temperature.......................................................+150C V , BRT, ENA, OSC, OV to GND...........................-0.3V to +6V Storage Temperature Range..............................-60C to +150C CC ISET, CCV, CS, FSET, CPLL, EXT to GND .-0.3V to (V + 0.3V) Lead Temperature (soldering, 10s)...................................+300C CC Continuous Power Dissipation (T = +70C) A TQFN (derate 16.9mW/C above +70C) ...................1349mW Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Electrical Characteristics (Circuit of Figure 1. V = 12V, V = V , CCV = 0.1F, T = 0C to +85C, unless otherwise noted. Typical values are at T = +25C.) IN SHDN IN A A PARAMETER CONDITIONS MIN TYP MAX UNITS V = V 4.5 5.5 IN CC IN Input Voltage Range V V = bypassed to GND through 1F capacitor 5.5 26.0 CC V = 26V 1 2 V = high, IN SHDN mA BRT = GND IN Quiescent Current V = V = 5V 1 2 IN CC SHDN = GND 10 A V Output voltage V = 5V, 6V < V < 26V, 0 < I < 10mA 4.7 5.0 5.3 V CC SHDN IN VCC V Short-Circuit Current 15 56 130 mA CC V UVLO Threshold Rising edge, hysteresis = 20mV 4.00 4.25 4.45 V CC STEP-UP CONVERTER V - CC EXT High Level 10mA from EXT to GND V V CC 0.1 EXT Low Level -10mA from EXT to V 0 0.1 V CC EXT On-Resistance EXT high or low 2 5 EXT Sink/Source Current EXT forced to 2V 1 A V - CC OSC High-Level Threshold V 0.4 V - CC OSC Midlevel Threshold 1.5 V 2.0 OSC Low-Level Threshold 0.4 V V = V 0.9 1.0 1.1 MHz OSC CC Operating Frequency V = open 675 750 825 OSC kHz V = GND 450 500 550 OSC PWM mode 10 Minimum Duty Cycle % Pulse skipping, no load 0 Maximum Duty Cycle 94 95 % CS Trip Voltage Duty cycle = 75% 85 100 115 mV CONTROL INPUT SHDN Logic-Input High Level 2.1 V SHDN Logic-Input Low Level 0.8 V BRT, ENA Logic-Input High Level 2.1 V BRT, ENA Logic-Input Low Level 0.8 V Maxim Integrated 2 www.maximintegrated.com