Figure 86. PSRR changes with Cb

10

100

1000

10000

100000

-70

-60

-50

-40

-30

Cin=100nF

Cb=100µF

Cin=100nF

Cb=1µF

Vcc = 5, 3.3 & 2.6V

Rfeed = 22k, Rin = 22k

Rg = 100Ω, RL = 8Ω

Tamb = 25°C

Frequency (Hz)

What is the PSRR?

The PSRR is the power supply rejection ratio. It is a kind of SVR in a determined frequency range.

The PSRR of a device, is the ratio between a power supply disturbance and the result on the output. We can say

that the PSRR is the ability of a device to minimize the impact of power supply disturbances to the output.

How do we measure the PSRR?

Figure 87. PSRR measurement schematic

Vripple

Vcc

Rin

Cin

Rg

100 Ohms

Cb

Rfeed

4

3

2

1

5

8

Vin-

Vin+

-

+

-

+

Bypass

Standby

Bias

6

Vout1

Vout2

Av=-1

TS4871

Vs-

Vs+

RL

7

5.13

Principle of operation

We fixed the DC voltage supply (Vcc), the AC sinusoidal ripple voltage (Vripple) and no supply capacitor Cs is

used.

The PSRR value for each frequency is:

PSRR(dB)=20xLog10 RmsVripple

Rms(Vs+−Vs−

TS4871

Application information

DS2547 - Rev 10

page 32/42