Chapter 4 Theory of Operation
D-to-A Converter
90
D-to-A Converter
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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