Regulator produces three outputs from 3V supplies

Edited by the Electronicstalk editorial team Oct 8, 2002

ADM8839/40 charge pump regulators are designed specifically for micro colour TFT LCDs used in cell phones with colour displays, PDAs, pocket PCs and other portable devices.

ADM8839/40 charge pump regulators are designed specifically for micro colour thin film transistor (TFT) liquid crystal displays (LCDs) used in cell phones with colour displays, PDAs, pocket PCs, and other portable devices.

Using high-performance charge pump technology, the ADM8839/40 generate the three voltages needed for the LCD controller and the panel transistors gate drivers: +5V 2%, +15V and -15V - all from a single 3V supply.

This multivoltage functionality makes the ADM8839/40 a cost-effective solution for a broad range of panels employing TFT technology.

The supply voltage is first doubled, and is then regulated by the ADM8839/40's low-dropout regulator (LDO) to provide a low ripple 5V output.

The 5V output then drives the charge pump section, which generates the +15 and -15V outputs.

If desired, the LDO can be shut down and an external LDO can be used in its place.

The ADM8839/40 ensures proper power sequencing for TFT panels by ramping the -15V supply before the +15V supply.

These regulators also feature a power saving shutdown mode with a Green Idle oscillator-enabling scheme.

This senses the load current that is flowing, and turns on the charge pump only when charge needs to be delivered to the 5V output.

An additional feature included with the ADM8840 is an integrated COM driver.

The COM driver helps prevent screen burn over time by alternating the polarity of the common line voltage on the display.

To accommodate this additional circuitry, the ADM8840 comes in a 32-lead lead frame chip-scale package (LFCSP), whereas the ADM8839 is available in a smaller 20-lead LFSCP.

The ADM8839/40 are manufactured using CMOS technology.

Samples are available today, with production quantities available in December 2002.

The ADM8839/40 are priced at $1.50 per unit in 1000 piece quantities.