TS4984FC Datasheet, PDF (23/30 Pages) STMicroelectronics – 1.2W Stereo Audio Power Amplifier with Active Low Standby Mode

TS4984FC
Application Information
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,
τ_in = (R_in + 2kΩ) x C_in (s) with R_in ≥ 5kΩ
must not reach the τ_in maximum value as indicated in the graph below in Figure 66.
Figure 66. 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 the previous rules, the TS4984 can reach near zero pop and click even with high
gains such as 20dB.
Example calculation:
With R_in = 22kΩ and a 20Hz, -3dB lower cut-off frequency, C_in = 361nF.
So, C_in =390nF with standard value which gives a lower cut-off frequency equal to 18.5Hz.
In this case, (R_in + 2kΩ) x C_in = 9.36ms.
When referring to the previous graph, if C_b =1µF and V_CC = 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 C_in and the gain benefits both the pop phenomena,
and the cost and size of the application.
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