EVALUATION KIT AVAILABLE MAX8790 Six-String White LED Driver with Active Current Balancing for LCD Panel Applications General Description Features Drives Six Parallel Strings with Multiple Series- The MAX8790 is a high-efficiency driver for white light- Connected LEDs per String emitting diodes (LEDs). It is designed for large liquid- crystal displays (LCDs) that employ an array of LEDs as 1.5% Current Regulation Accuracy Between Strings the light source. A current-mode step-up controller drives Low 450mV Feedback Voltage at Full Current up to six parallel strings of multiple series-connected Improves Efficiency LEDs. Each string is terminated with ballast that achieves Step-Up Controller Regulates the Output Just Above 1.5% current regulation accuracy, ensuring even bright- the Highest LED String Voltage ness for all LEDs. The MAX8790 has a wide input voltage Full-Scale LED Current Adjustable from 15mA to range from 4.5V to 26V, and provides a fixed 20mA or 25mA, or Preset 20mA adjustable 15mA to 25mA full-scale LED current. Wide 100:1 Dimming Range The MAX8790 has two dimming-control modes to enable Programmable Dimming Control: Direct DPWM or a wide variety of applications. In direct DPWM mode, the Analog Dimming LED current is directly turned on and off by a PWM signal. 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 Open and Short LED Protections signal and linearly controls the LED current down to Output-Overvoltage Protection 12.5%. Below 12.5%, digital dimming is added to allow Wide Input Voltage Range from 4.5V to 26V lower average LED current down to 1%. Both control methods provide 100:1 dimming range. External MOSFET Allows a Large Number of LEDs per String The MAX8790 has multiple features to protect the control- ler from fault conditions. Separate feedback loops limit the 500kHz/750kHz/1MHz Switching Frequency output voltage if one or more LEDs fail open or short. The Small, 20-Pin, 4mm x 4mm TQFN Package controller features cycle-by-cycle current limit to provide Simplified Operating Circuit consistent operation and soft-start capability. A thermal- shutdown circuit provides another level of protection. L1 D1 V OUT V IN The step-up controller uses an external MOSFET, which C IN provides good efficiency and allows for scalable output 0.1F power and maximum operating voltage. Low feedback voltage at each LED string (450mV) helps reduce power IN SHDN N1 EXT loss. The MAX8790 features selectable switching frequen- V CC CS cy (500kHz, 750kHz, or 1MHz), which allows trade-offs FSET ISET between external component size and operating efficiency. Rs MAX8790 The MAX8790 is available in a thermally enhanced, GND BRT lead(Pb)-free, 20-pin, 4mm x 4mm, TQFN package. R1 OV N.C. OSC Applications Notebook, Subnotebook, and Tablet Computer Displays R2 N.C. CPLL Handy Terminals CCV FB1 Ordering Information FB2 FB3 ENA PKG FB4 PART TEMP RANGE PIN-PACKAGE EP CODE FB5 FB6 20 Thin QFN MAX8790ETP+ -40C to +85C T2044-3 (4mm x 4mm) Pin Configuration appears at end of data sheet. +Denotes a lead(Pb)-free/RoHS-compliant package. 19-0658 Rev 1 5/14MAX8790 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 20-Pin Thin QFN (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 IN V = high mA SHDN 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