TS4984FC datasheet(23/30 Pages) STMICROELECTRONICS

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TS4984FC

Application Information

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4.8

Pop performance

Pop performance is intimately linked with the size of the input capacitor Cin and the bias voltage

bypass capacitor Cb.

The size of Cin is dependent on the lower cut-off frequency and PSRR values requested. The

size of Cb is dependent on THD+N and PSRR values requested at lower frequencies.

Moreover, Cb determines the speed with which the amplifier turns ON. In order to reach near

zero pop and click, the equivalent input constant time,

τin =(Rin +2kΩ)xCin (s) with Rin ≥ 5kΩ

must not reach the

τin maximum value as indicated in the graph below in Figure 66.

By following the previous rules, the TS4984 can reach near zero pop and click even with high

gains such as 20dB.

Example calculation:

With Rin =22kΩ and a 20Hz, -3dB lower cut-off frequency, Cin = 361nF.

So, Cin =390nF with standard value which gives a lower cut-off frequency equal to 18.5Hz.

In this case, (Rin +2kΩ)x Cin =9.36ms.

When referring to the previous graph, if Cb =1µF and VCC = 5V, we read 20 ms max.

This value is twice as high as our current value, thus we can state that pop and click will be

reduced to its lowest value. Minimizing both Cin and the gain benefits both the pop phenomena,

and the cost and size of the application.

Figure 66.

τin max. versus bypass capacitor

120

160

Vcc=5V

Vcc=3.3V

Vcc=2.6V

Tamb=25

°C

Bypass Capacitor Cb ( F)

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