TS4984 datasheet(23/29 Pages) STMICROELECTRONICS

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Application Information

TS4984

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4.7 Shutdown time

When the standby command is set, the time required to put the two output stages in high impedance and

the internal circuitry in shutdown mode is a few microseconds.

Note:

In shutdown mode, Bypass pin and Vin- pin are short-circuited to ground by internal switches. This allows for

the quick discharge of the Cb and Cin capacitors.

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 is:

tin =(Rin+2 kΩ)x Cin (s) with Rin ≥ 5kΩ

must not reach the

τin maximum value as indicated in the graph below in Figure 68.

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

20 dB.

Example calculation

With Rin =22kΩ and a 20 Hz, -3 db low cut-off frequency, Cin = 361 nF. So, Cin =390 nF with standard

value which gives a lower cut-off frequency equal to 18.5 Hz. In this case, (Rin +2 kΩ)x Cin =9.36ms.

When referring to the previous graph, if Cb =1 µF and Vcc = 5 V, 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 68:

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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