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How can a low-noise power supply be created using an LDO regulator?

If input voltage (VIN) has noise such as ripples, it is advisable to select an LDO regulator with a high ripple rejection ratio (R.R.).

R.R. is a figure of merit that represents the capability of an LDO regulator to filter out the ripples superimposed on VIN from the output.

Use R.R. as a guide when using an LDO regulator in analog and other highly noise-sensitive circuits. In cases where an LDO regulator is preceded by a DC-DC converter, an LDO regulator with a higher R.R. is more suitable for CMOS sensor and other high-precision analog circuits because a high-R.R. LDO regulator provides an excellent noise suppression capability. The ripple rejection ratio is calculated as follows:

Ripple rejection ratio

R.R. varies with ripple frequency. R.R. decreases as ripple frequency increases.

The R.R. curve shown in Figure 2 indicates that 200-Hz ripples can be suppressed to roughly 1/30000th whereas 100,000-Hz ripples can be suppressed to only roughly 1/800th.

The ripple rejection ratio is also called the power supply rejection ratio (PSRR) or the supply voltage rejection ratio (SVRR).

Figure 1 Ripple rejection
Figure 1 Ripple rejection

Figure 2 Ripple rejection ratio (R.R.) vs. frequency
Figure 2 Ripple rejection ratio (R.R.) vs. frequency

For LDO’s ripple rejection ratio, please refer to
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