9 Power Supply Recommendations

The device requires two different power-supply voltages. 1.9-V DC is required for the VA19 power bus and 1.1-V DC is required for the VA11 and VD11 power buses.

The power-supply voltages must be low noise and provide the needed current to achieve rated device performance.

There are two recommended power supply architectures:

1. Step down using high-efficiency switching converters, followed by a second stage of regulation to provide switching noise reduction and improved voltage accuracy.
2. Directly step down the final ADC supply voltage using high-efficiency switching converters. This approach provides the best efficiency, but care must be taken for switching noise to be minimized to prevent degraded ADC performance.

TI WEBENCH® Power Designer can be used to select and design the individual power supply elements needed: see the WEBENCH® Power Designer

Recommended switching regulators for the first stage include LMS3635-Q1, LMS3655-Q1, TPSM84424 and similar devices.

Recommended low drop-out (LDO), low-noise linear regulators include the TPS7A84, TPS7A83A, TPS7A47 and similar devices.

For the switcher only approach, the ripple filter must be designed to provide sufficient filtering at the switching frequency of the DC-DC converter and harmonics of the switching frequency. Make a note of the switching frequency reported from WEBENCH® and design the EMI filter and capacitor combination to have the notch frequency centered as needed. Each application will have different tolerances for noise on the supply voltage so strict ripple requirements are not provided. Figure 9-1 and Figure 9-2 illustrate the two approaches.

FB = ferrite bead filter.

Figure 9-1 LDO Linear Regulator Approach Example

Ripple filter notch frequency to match the fs of the buck converter.

FB = ferrite bead filter.

Figure 9-2 Switcher-Only Approach Example