The AD7849 is a 14-/16-bit serial input multiplying DAC. The DAC architecture ensures excellent differential linearity performance; Class A products guarantee 14-bit monotonicity over the rated temperature range, and all other grades guarantee 16-bit monotonicity. During power-up and shutdown (when the supply voltage changes erratically), V
OUTThe pins are clamped at 0 V through a low impedance path. To prevent the output of A3 from shorting to 0 V, the transmission gate G1 is also opened. This condition continues until the power supply settles down and a valid word is written to the DAC register, at which point G2 turns on and G1 closes. The input is controlled via the reset input (RST IN), and both transmission gates can also be controlled externally. For example, if the RST IN input is driven by a battery monitor chip, the RST IN input will go low to turn G1 on and G2 off when power down or power down. To re-enable the output, the DAC must be reloaded to bring RST IN high. Conversely, the user can control other parts of the system using the on-chip voltage detector output (RST OUT).
The AD7849 has a versatile serial interface structure that can be controlled through three lines to facilitate optoisolator applications.
SDOUT is an on-chip shiftregisteroutput, which can be daisy-chained to program devices in multichannel systems. This function is controlled by a DCEN (daisy-chained) input.
The BIN/COMP pin sets the DAC encoding method. When BIN/COMP is set to 0, the encoding method is standard binary; If set to 1, the encoding method is twos complement. This allows the user to reset the DAC to 0 V in both unipolar and bipolar output ranges.
The device is available in 20-pin DIP and 20-pin SOIC packages.