10.2.1.1 Design Requirements

A detailed design procedure is based on a design example. For this design example, use the parameters listed

in Table 10-1 as the input parameters.

Table 10-1. Design Example Parameters

DESIGN PARAMETER

VALUE

5.5 V

2.5 V

REF7025 input capacitor

10-µF

REF7025 output capacitor

10-µF

10.2.1.2 Detailed Design Procedure

10.2.1.2.1 Input and Output Capacitors

A 1 μF to 10 μF bypass capacitor should be connected to the input to improve transient response in applications

where the supply voltage may fluctuate. Connect an additional 0.1 μF capacitor in parallel to reduce high

frequency supply noise.

A low ESR capacitor of 1 μF to 100 μF must be connected to the output to improve stability and help filter

out high frequency noise. Best performance and stability is attained with low-ESR output capacitors with an

ESR from 10 mΩ to 400 mΩ. For very low noise applications, special care must be taken with X7R and

other MLCC capacitors due to their piezoelectric effect. Mechanical vibration can transduce to voltage via the

piezoelectric effect which appears as noise in the μV range, potentially dominating the noise of the REF70. More

information on how the piezoelectric effect can be explored in systems can be found in Stress-induced outbursts:

Microphonics in ceramic capacitors (Part 1) and Stress-induced outbursts: Microphonics in ceramic capacitors

(Part 2). It is recommended that to use film capacitors for noise sensitive applications.

The transient startup response of the REF70 is shown in Figure 10-2. The startup response of the REF70 family

is dependent on the output capacitor. While larger capacitors will decrease the output noise, they will increase

the startup response.

REF70

SNAS781D – OCTOBER 2020 – REVISED DECEMBER 2021

www.ti.com

26

Submit Document Feedback

Copyright © 2021 Texas Instruments Incorporated

Product Folder Links: REF70