MAX1621

19-1214; Rev 1; 1/98 NUAL KIT MA ATION EET H S A EVALU T WS DA O L L O F Digitally Adjustable LCD Bias Supplies General Description The MAX1620/MAX1621 convert a 1.8V to 20V battery voltage to a positive or negative LCD backplane bias voltage. Backplane bias voltage can be automatically disabled when the display logic voltage is removed, protecting the display. These devices use very little PC board area, come in ultra-small QSOP packages, and require only small, low-profile external components. Output voltage can be set to a desired positive or negative voltage range with external resistors, and adjusted over that range with the on-board digital-to-analog converter (DAC) or with a potentiometer. The MAX1620/ MAX1621 include a 5-bit DAC, allowing digital software control of the bias voltage. The MAX1620 uses up/down digital signaling to adjust the DAC, and the MAX1621 uses the System Management Bus (SMBus™) 2-wire serial interface. These devices use a low-cost, external, N-channel MOSFET power switch or NPN transistor, and can be configured for positive or negative output voltages. Operating current is a low 150µA, typically provided from a display’s logic supply of 3.0V to 5.5V. The MAX1620/MAX1621 are available in a 16-pin QSOP package. o 1.8V to 20V Battery Input Voltage o Automatic Disable when Display Logic is Shut Down o Extremely Small QSOP Package o 32-Level Internal DAC o SMBus Serial Interface (MAX1621) o Positive or Negative Output Voltage Features MAX1620/MAX1...