MAX749 19-0143 Rev 1 2/95 Digitally Adjustable LCD Bias Supply General Description Features The MAX749 generates negative LCD-bias contrast +2.0V to +6.0V Input Voltage Range voltages from 2V to 6V inputs. Full-scale output voltage Flexible Control of Output Voltage: can be scaled to -100V or greater, and is digitally Digital Control adjustable in 64 equal steps by an internal digital-to- analog converter (DAC). Only seven small surface- Potentiometer Adjustment mount components are required to build a complete PWM Control supply. The output voltage can also be adjusted using Output Voltage Range Set by One Resistor a PWM signal or a potentiometer. Low, 60A Max Quiescent Current A unique current-limited control scheme reduces supply current and maximizes efficiency, while a high switching 15A Max Shutdown Mode frequency (up to 500kHz) minimizes the size of external Small Size 8-Pin SO and Plastic DIP Packages components. Quiescent current is only 60A max and is reduced to under 15A in shutdown mode. While shut down, the MAX749 retains the voltage set point, simpli- fying software control. The MAX749 drives either an external P-channel MOSFET or a PNP transistor. Applications Ordering Information Notebook Computers PART TEMP. RANGE PIN-PACKAGE Laptop Computers MAX749CPA 0C to +70C 8 Plastic DIP Palmtop Computers MAX749CSA 0C to +70C 8 SO Personal Digital Assistants MAX749C/D 0C to +70C Dice* Communicating Computers MAX749EPA -40C to +85C 8 Plastic DIP Portable Data-Collection Terminals MAX749ESA -40C to +85C 8 SO * Contact factory for dice specifications. Typical Operating Circuit Pin Configuration V +5V IN TOP VIEW R SENSE 0.1F 1 8 V+ CS 1 8 V+ CS 2 7 ADJ MAX749 DHI DIGITAL 2 7 ADJ DHI ADJUST -V MAX749 3 6 OUT 3 6 CTRL DLOW DLOW ON/OFF CTRL 5 4 4 5 FB GND GND FB R DIP/SO FB C COMP Maxim Integrated Products 1 Call toll free 1-800-998-8800 for free samples or literature. EVALUATION KIT MANUAL FOLLOWS DATA SHEETDigitally Adjustable LCD Bias Supply ABSOLUTE MAXIMUM RATINGS V+................................................................................-0.3V, +7V Operating Temperature Ranges: CTRL, ADJ, FB, DLOW, DHI, CS.....................-0.3V, (V+ + 0.3V) MAX749C A........................................................0C to +70C Continuous Power Dissipation (T = +70C) A MAX749E A.....................................................-40C to +85C Plastic DIP (derate 9.09mW/C above +70C) ............727mW Storage Temperature Range .............................-65C to +160C SO (derate 5.88mW/C above +70C).........................471mW Lead Temperature (soldering, 10sec) .............................+300C Stresses beyond those listed under Absolute Maximum Rating 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 (2V < V+ < 6V, T = T to T , unless otherwise noted.) A MIN MAX PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS V+ Voltage 26V FB Source Current IFBS On power-up or reset, VFB = 0V (Note 1) 12.80 13.33 13.86 A Zero-Count FB Current V = 0V 0.45 0.55 I FB FBS Full-Count FB Current V = 0V 1.43 1.53 I FB FBS FB Offset Voltage 15 mV DAC Step Size (Note 2) Monotonicity guaranteed, V = 0V 1.00 1.56 2.12 %I FB FBS DAC Linearity (Note 2) V = 0V 1 %I FB FBS Supply Rejection V+ = 2V to 6V, full-count current 1.5 %I FBS Switching Frequency 100 to 500 kHz Logic Input Current 0V < V < V+, CTRL, ADJ 100 nA IN Logic High Threshold (Note 3) V CTRL, ADJ 1.6 V IH Logic Low Threshold (Note 3) V CTRL, ADJ 0.4 V IL Quiescent Current 60 A Shutdown Current 15 A V+ to CS Voltage Current-limit trip voltage 110 140 180 mV DHI Source Current V+ = 2V, V = 1V 24 50 mA DHI DHI Drive Level No load V+ - 50mV V+ V DLOW On Resistance V+ = 2V, V = 0.5V 510 DLOW Note 1: The device is in regulation when V = 0V (see Figures 3 - 6). FB Note 2: These tests performed at V+ = 3.3V. Operation over supply range is guaranteed by supply rejection test of full-count current. Note 3: V is guaranteed by design to be 1.8V min for V+ = 2V to 6V for T = T to T . V is guaranteed by design from IH A MIN MAX IL T = T to T . A MIN MAX TIMING CHARACTERISTICS T = +25C T = TMIN to T A A MAX PARAMETER SYMBOL CONDITIONS UNITS MIN TYP MAX MIN MAX V+ = 2V 125 300 400 Minimum Reset Pulse Width t ns R V+ = 5V 25 85 100 Minimum Reset Setup t Not tested 0 0 ns RS Minimum Reset Hold t Not tested 0 0 ns RH V+ = 2V 15 85 100 Minimum ADJ High Pulse Width t ns SH V+ = 5V 10 85 100 V+ = 2V 170 400 500 Minimum ADJ Low Pulse Width t ns SL V+ = 5V 60 150 200 V+ = 2V 70 200 250 Minimum ADJ Low to CTRL Low t ns SD V+ = 5V 20 85 100 2 MAX749