Power Supplies; Dc/Dc Converter Circuit; Figure 4-1. Dc/Dc Converter And Transformer Driver Circuit (Schematic) - Texas Instruments ADS131B26Q1EVM-PDK User Manual

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4 Power Supplies

This section details the EVM power supplies, ADC analog and digital supply options, and the PCB layout and
decoupling guidelines.

4.1 DC/DC Converter Circuit

As mentioned previously in
connector J9. For information about the PHI pins and power connections, see
A 3.3-V LDO output on the PHI (ISO_3V3) is used to power the controller side of the isolation barrier, including
the digital isolators, onboard 8.192-MHz oscillator, and D flip-flop clock divider circuit. ISO_3V3 is also the
default option to power the transformer driver (SN6505B-Q1, U6) and generate the supplies used on the ADC
side of the isolation barrier. U6 can also be powered by the raw USB supply (EVM_RAW_5V) by uninstalling
R96 and installing R97.
By default, the SN6505B-Q1 uses an internal 420-kHz clock to set the transformer switching frequency. This
clock operates asynchronously to the ADS131B26-Q1 internal clock (CLK = 8.192 MHz). However, the EVM
also supports an external ADC clock, which can be provided either by enabling the onboard oscillator (Y1) or by
connecting a clock from an external source to the onboard SMA connector (J10). When an external clock is used
for the ADC, this signal is divided by a factor of 16 using the dual D-type flip-flops (U7 and U8) and shared with
the SN6505B-Q1 CLK input. The SN6505B-Q1 internally divides this clock input by another factor of 2, resulting
in a transformer switching frequency that is synchronous with the ADC clock. Any remaining switching noise at
the transformer output detected by the ADS131B26-Q1 aligns with a null in the ADC sinc3 digital filter response
and be significantly attenuated.

Figure 4-1. DC/DC Converter and Transformer Driver Circuit (Schematic)

SBAU413 – OCTOBER 2022
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Section 1, power to the EVM can be supplied entirely by the PHI controller through
Figure 4-1 shows the DC/DC converter and transformer driver circuits.
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Power Supplies
Table 3-1.
ADS131B26Q1EVM-PDK Evaluation Module 11