Agilent Technologies 34970A, Service Manual, Page: 156 / 273

Analog Output
Components in this discussion are located on the A1 circuit assembly
(34907-66501). The schematics are included in Chapter 8 starting on
page 261.
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.
Chapter 5 Theory of Operation
Multifunction Module
154