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Chapter 4 Theory of Operation
D-to-A Converter
84
D-to-A Converter
Referring to the schematic shown on page 123, all reference voltages of power
circuits are derived from the internal voltage reference of system DAC U21.
The system DAC track/hold amplifier outputs are used to provide controllable
reference voltages to three power circuits. The system DAC is programmed
and responds to the main controller via internal 3-wire serial data bus SERCLK,
SERRBK, and SERSTB. The system DAC is mutiplexed to 6 track/hold
amplifiers through U27. Each track/hold amplifier is refreshed approximately
every 1 msec to maintain its output setting. Changes to track/hold amplifier
outputs are accomplished by dwelling on that position for an extended period.