TS4872_05 datasheet(26/29 Pages) STMICROELECTRONICS

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Fig. 84 : PSRR changes with Cb

■ Note on PSRR measurement

What is the PSRR ?

The PSRR is the Power Supply Rejection Ratio.

It’s 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

minimize

the

impact

power

supply

disturbances to the output.

How we measure the PSRR ?

For PSRR measurement schematic see figure 85

Fig. 85 : PSRR measurement schematic

■ Principle of operation

• We fixed the DC voltage supply (Vcc)

• We fixed the AC sinusoidal ripple voltage

(Vripple)

• No bypass capacitor Cs is used

The PSRR value for each frequency is :

Remark : The measure of the Rms voltage is not a

Rms selective measure but a full range (2 Hz to

125 kHz) Rms measure. It means that we

measure the effective Rms signal + the noise.

100

1000

10000

100000

-70

-60

-50

-40

-30

Cin=100nF

Cb=100

µF

Cin=100nF

Cb=1

µF

Vcc = 5 & 2.6V

Rfeed = 22k, Rin = 22k

Rg = 100

Ω, RL = 8Ω

Tamb = 25

°C

Frequency (Hz)

Vripple

Vcc

Rin

Cin

100 Ohms

Rfeed

Vin-

Vin+

Bypass

Standby

Bias

Vout1

Vout2

Av=-1

TS4872

Vs-

Vs+

PSRR d B

() = 20 x Log

Rm s Vrippl e

()

Rm s Vs + - Vs-

()

---------------------------------------------

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