Chapter 4 Theory of Operation
D-to-A Converter
86
D-to-A Converter
Referring to the schematic shown on page 129, all reference voltages of power
circuits are derived from the internal voltage reference of system DAC U12 on
the top board. 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 U13 on the top board. Each
track/hold amplifier is refreshed approximately every 13 msec to maintain its
output setting. Changes to track/hold amplifier outputs are accomplished by
dwelling on that position for an extended period.
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