Datasheet

Application information TS4990
22/33 Doc ID 9309 Rev 13
mode, the bypass pin and V
in
pin are short-circuited to ground by internal switches. This
allows a quick discharge of 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,
τ
in
= (R
in
+ 2kΩ)xC
in
(s) with R
in
≥ 5kΩ
must not reach the τ
in
maximum value as indicated in Figure 63 below.
Figure 63. τ
in
max. versus bypass capacitor
By following the previous rules, the TS4990 can reach near zero pop and click even with
high gains such as 20 dB.
Example:
With R
in
=22kΩ and a 20 Hz, -3 dB low cut-off frequency, C
in
=361nF. So, C
in
=390nF
with standard value which gives a lower cut-off frequency equal to 18.5 Hz. In this case,
(R
in
+2kΩ)xC
in
= 9.36ms. By referring to the previous graph, if C
b
= 1 µF 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 phenomenon, and the cost and size
of the application.
1234
0
40
80
120
160
Vcc=5V
Vcc=3.3V
Vcc=2.6V
Tamb=25 ° C
in max. (ms)
Bypass Capacitor Cb ( F)