MAX1578/MAX1579 MAX1578/MAX1579 19-3359 Rev 1 8/05 Complete Bias and White LED Power Supplies for Small TFT Displays General Description Features Four Regulators in One Package The MAX1578/MAX1579 provide four regulated outputs to meet all the voltage requirements for small active- Bias Power Using Charge Pumps matrix TFT-LCD displays in handheld devices where +5V at 25mA for Source Driver minimum external components and high efficiency are +15V at 100A for V ON required. Each device consists of three advanced -10V at 100A for V OFF charge pumps for LCD bias power and a step-up con- No External Diodes Required verter for driving up to 8 series white LEDs for back- Output Sequencing POS, NEG, and MAIN Are Autodischarged lighting. The input voltage range is from 2.7V to 5.5V. During Shutdown The charge pumps provide fixed +5V, +15V, and -10V LED Backlight Power Using Boost Converter for the LCD bias circuits. No external diodes are need- Series LED Connection for Uniform Illumination ed. A high-efficiency, fractional (1.5x/2x) charge pump Supports Up to 8 LEDs at 25mA (max) followed by a low-dropout linear regulator provides +5V 900mW (max) Power to power the source driver. Automatic mode changing PWM or Analog Dimming Control achieves the highest conversion efficiency. Two multi- Overvoltage Protection stage, high-voltage charge pumps generate +15V and Low Input/Output Ripple -10V to provide V and V , respectively. Utilizing a ON OFF Soft-Start with Zero Inrush Current unique clocking scheme and internal drivers, these Fast 1MHz PWM Operation for Small charge pumps eliminate parasitic charge-current glitch- Component Size es and reduce maximum input current, resulting in low Temperature Derating Function (MAX1579) electromagnetic emissions. The outputs are sequenced High Efficiency during startup and shutdown. In shutdown, the outputs Bias: 83% (5.0V at 25mA, 15V/-10V at 100A) are discharged to zero. LED: 84% (6 LEDs at 20mA) The high-efficiency inductor step-up converter drives Uses Only Ceramic Capacitors and Only One up to 8 white LEDs in series with a constant current to Inductor provide backlighting. The series connection allows the Independent Enable Inputs for LED and Bias LED currents to be identical for uniform brightness and Power minimizes the number of traces to the LEDs. The Thermal-Shutdown Protection MAX1578 regulates constant LED current over the entire temperature range. The MAX1579 features a tem- 1A Shutdown Current perature derating function to avoid overdriving the Tiny 4mm x 4mm Thin QFN Package white LEDs during high ambient temperatures, enabling higher drive current below +42C. Pin Configuration The MAX1578/MAX1579 are available in space-saving 24-lead 4mm x 4mm thin QFN packages. 18 17 16 15 14 13 Applications PDAs, Palmtops LCD Displays with C1N 19 12 GND White LED Backlight Smart Phones 20 11 ONBIAS C2N Internet Appliances 21 10 NEG IN 22 MAX1578 9 CD2 C2P Ordering Information MAX1579 8 CD1 C1P 23 PART TEMP RANGE PIN-PACKAGE V 24 7 PMPB DD + 24 Thin QFN 4mm x 4mm 1 2 3 4 5 6 MAX1578ETG -40C to +85C (T2444-4) 24 Thin QFN 4mm x 4mm MAX1578ETG+ -40C to +85C (T2444-4) THIN QFN 4mm x 4mm + Denotes lead-free package. See Figure 3 for Typical Application Circuit. Ordering Information continued at end of data sheet. Maxim Integrated Products 1 For pricing delivery, and ordering information please contact Maxim/Dallas Direct at 1-888-629-4642, or visit Maxims website at www.maxim-ic.com. EVALUATION KIT AVAILABLE MAIN PGND CU1 LX CU2 OUT CU3 CTRL POS CS PMP COMPComplete Bias and White LED Power Supplies for Small TFT Displays ABSOLUTE MAXIMUM RATINGS IN, CS, C1N, C2N, MAIN, ONBIAS, V to GND.....-0.3V to +6V NEG, CD2 to GND..................................................+0.3V to -12V DD CTRL to GND..................-0.3V to the lesser of +6V or (V + 2V) C1P, C2P to GND ...........................................-0.3V to (V + 6V) IN IN LX, OUT to GND.....................................................-0.3V to +37V PMP, PMPB to GND ................................-0.3V to (V + 0.3V) MAIN COMP to GND .............................................-0.3V to (V + 0.3V) GND to PGND .......................................................-0.3V to +0.3V IN CU1 to MAIN ............................................................-0.3V to +6V I ...................................................................................1.0A LX RMS CU2 to CU1 ..............................................................-0.3V to +6V Continuous Power Dissipation (T = +70C) A CU3 to CU2 ..............................................................-0.3V to +6V 24-Pin 4mm x 4mm Thin QFN CU3 to POS ............................................................-0.3V to +18V (derate 20.8mW/C above +70C) .............................1667mW CU3 to GND ...........................................................-0.3V to +18V Short-Circuit Duration (MAIN, POS, NEG)..................Continuous POS to GND ...........................................................-0.3V to +18V Operating Temperature Range ...........................-40C to +85C CD1 to MAIN ..........................................................+0.3V to -12V Junction Temperature......................................................+150C CD1 to GND .............................................................+0.3V to -6V Storage Temperature Range .............................-65C to +150C CD2 to CD1 ..............................................................+0.3V to -6V Lead Temperature (soldering, 10s) ................................ +300C NEG to CD2..............................................................+0.3V to -6V 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 3, V = 3V, CTRL = ONBIAS = IN, T = -40C to +85C, typical values are at T = +25C, unless otherwise noted. Note 1) IN A A PARAMETER CONDITIONS MIN TYP MAX UNITS IN Operating Supply Range 2.7 5.5 V IN Undervoltage-Lockout (UVLO) Rising edge, 30mV hysteresis 2.1 2.35 2.6 V Threshold IN Quiescent Current Switching 3 5 mA T = +25C 0.4 1 A IN Shutdown Current V = V = 0V A CTRL ONBIAS T = +85C 1 A Thermal Shutdown Rising temperature, 20C hysteresis (typ) +160 C MAIN CHARGE PUMP WITH LINEAR REGULATOR Main Pump Efficiency I = 25mA, V = 3.9V 83 % LOAD IN V 3.8V in 1.5x mode 9 20 V Charge-Pump Open-Loop IN DD Output Impedance V 3.0V in 2.0x mode 7.5 20 IN Operating Frequency 200 250 300 kHz V Output Voltage Charge-pump pause threshold 5.2 5.5 5.7 V DD V Fall i ng S w i tchover t o 2.0x Mod e 3.75 3.85 3.95 V IN V Ri sing S w i tchover to 1.5x Mod e 3.8 3.9 4.0 V IN Quiescent Current V = 0V, ONBIAS = IN 0.87 1.30 mA CTRL (Charge Pumps Only) V Regulation Voltage 0.1mA < I < 25mA 4.9 5.0 5.1 V MAIN LOAD Discharge Switch Resistance V = 0V 1 3 k ONBIAS at V MAIN POS, NEG CHARGE PUMPS Operating Frequency 12.0 15.6 19.5 kHz Duty Cycle 50 % POS Pump Efficiency I = 100A 97 % LOAD POS Output Voltage I = 0 to 100A 13.9 14.7 15.3 V LOAD P OS D i scharg e S w i tch Resis tance V = 0V 3 6 k ONBIAS NEG Pump Efficiency I = -100A 97 % LOAD 2 MAX1578/MAX1579