Agilent 34970A/34972A Data Acquisition / Switch Unit

Chapter 5 Theory of Operation
Multifunction Module
Analog Output
Components in this discussion are located on the A1 circuit assembly
(34907-66501).
A simplified block diagram of the analog output channels is shown below.
Communication with each DAC (U503 and U504) is via three lines:
SERSTB, DACCLK, and SERDAT. Each DAC has a voltage output of ±3
V. U505 and U506 amplify this voltage to the ±12V output.
A DC/DC converter is used to provide the ± 15V supplies to U505 and
U506. The ± 15V supplies also are used at the input of the totalizer.
U502 provides the –5 V supply used by the DACs.
A line from U101 P0.4 is used to control the output of U510. After a reset
or power-up, U510 is held in the shutdown state. U101 turns on the DC/
DC converter in response to commands from the main controller. The
main controller paces the turn on of the DC/DC converters to ensure that
if multiple modules are installed, the backplane power supply is not
pulled down by the in-rush current of the DC/DC converters.
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