TS4990 datasheet(22/32 Pages) STMICROELECTRONICS

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Application information

TS4990

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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)xCin (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

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 =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 +2kΩ)xCin = 9.36ms. By referring to the previous graph, if Cb = 1 µF and VCC =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 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:

In order to reach the best performance of the differential function, R1 and R2 should be

matched at 1% max.

120

160

Vcc=5V

Vcc=3.3V

Vcc=2.6V

Tamb=25

°C

Bypass Capacitor Cb ( F)

VDIFF

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