TS4890IST datasheet(40/46 Pages) STMICROELECTRONICS

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Application information

TS4890

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DocID8396 Rev 7

How to use the PSRR curves

We have finished a design and we have chosen for the components:

•

Rin = Rfeed = 22 k

Ω

•

Cin=100 nF

•

Cb=1 µF

Now, in Figure 16, we can see the PSRR (input grounded) vs frequenc y curves. At 217 Hz,

we have a PSRR value of -36 dB. In reality we want a value about -70dB. So, we need a

gain of 34 dB. Now, in Figure 15 we can see the effect of Cb on the PSRR (input grounded)

vs frequency. With Cb=100 µF, we can reach the -70 dB value. The process to obtain the

final curve (Cb=100 µF, Cin=100 nF, Rin=Rfeed=22 k

Ω) is a simple transfer point by point

on each frequency of the curve on Figure 16 to the curve on Figure 15. The measurement

result is shown on the next figure.

Figure 109. PSRR changes with Cb

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.

C12

1 µF

Led 3 mm

S1, S2, S6, S7

2 mm insulated plug

10.16 mm pitch

3 connector 2.54 mm

pitch

P1, P2

PCB phono jack

TS4890ID or TS4890IS

Table 12. Components 4

Designator

Part type

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