TS4984 Datasheet, PDF (23/29 Pages) STMicroelectronics – 2 x 1W Stereo audio power amplifier with active low standby mode

Application Information
TS4984
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 C_b and C_in capacitors.
4.8 Pop performance
Pop performance is intimately linked with the size of the input capacitor C_in and the bias voltage bypass
capacitor C_b.
The size of C_in is dependent on the lower cut-off frequency and PSRR values requested. The size of C_b
is dependent on THD+N and PSRR values requested at lower frequencies.
Moreover, C_b determines the speed with which the amplifier turns ON. In order to reach near zero pop
and click, the equivalent input constant time is:
t_in = (Rin + 2 kΩ) x C_in (s) with R_in ≥ 5 kΩ
must not reach the τ_in maximum value as indicated in the graph below in Figure 68.
Figure 68: τ_in max. versus bypass capacitor
160 ^Tamb=25°C
Vcc=3.3V
120
Vcc=2.6V
80
40
Vcc=5V
0
1
2
3
4
Bypass Capacitor Cb ( F)
By following previous rules, the TS4984 can reach near zero pop and click even with high gains such as
20 dB.
Example calculation
With R_in = 22 kΩ and a 20 Hz, -3 db low cut-off frequency, C_in = 361 nF. So, C_in =390 nF with standard
value which gives a lower cut-off frequency equal to 18.5 Hz. In this case, (R_in + 2 kΩ) x C_in = 9.36 ms.
When referring to the previous graph, if C_b =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 C_in and the gain benefits both the pop phenomena, and the cost and size of the
application.
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