TS4990 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TS4990' PDF : 33 Pages View PDF
Application information
TS4990
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,
τ in = (Rin + 2kΩ) x Cin (s) with Rin ≥ 5kΩ
must not reach the τ in maximum value as indicated in Figure 63 below.
Figure 63. 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 TS4990 can reach near zero pop and click even with
high gains such as 20 dB.
Example:
With Rin = 22 kΩ 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 + 2kΩ) x Cin = 9.36ms. By 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 phenomenon, and the cost and size
of the application.
4.9
Application example: differential input, BTL power amplifier
The schematics in Figure 64 show how to configure the TS4990 to work in differential input
mode. The gain of the amplifier is:
GVDIFF
=
2
R-----2-
R1
In order to reach the best performance of the differential function, R1 and R2 should be
matched at 1% max.
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