The AD8842 has eight general-purpose digitally controlled voltage regulators, and the TrimDAC® feature can replace the mechanical regulator function in the new design. It is ideal for AC or DC gain control of signals up to 50 kHz bandwidth. The four-quadrant multiplication function can be used for signal flipping and modulation, which is common in video vertical deflection circuits.
The AD8842 has eight built-in voltage output digital-to-analog converters (DACs), each with a separate voltage input. The new current transmitter amplifier design performs a four-quadrant multiplication function, with a single-ended amplifier at the current output controlling the digital-analog controller. This approach improves constant input resistance performance compared to voltage-switched DACs previously used in TrimDAC circuits, eliminating the need for an input buffer amplifier.
Each DAC has its own DAC registers to maintain its output state, which are updated by an internal serial to parallel shift register that loads data from a standard three-wire serial input digital interface. The data word composed of 12 data bits is synchronously transmitted to the serial input register, which is decoded, and the first 4 bits can determine the address of the DAC register that needs to be loaded with the last 8 bits. By using the serial data output pins on opposite ends of the serial registers, multiple DACs can be simply daisy-chained without the need for additional external decoding logic.
When powered from a ±5 V supply, the AD8842 consumes only 95 mW. For 5 V single-supply applications, refer to the DAC-8841. The AD8842 is pin-DAC8840 compatible with 1 MHz multiplication bandwidth devices. It is available in 24-pin molded DIP and surface-mount SOL-24 packages.