TS4995 datasheet(20/26 Pages) STMICROELECTRONICS

20 / 26 page

Application information

TS4995

20/26

4.5

Decoupling of the circuit

Two capacitors are needed to correctly bypass the TS4995: a power supply bypass

capacitor CS and a bias voltage bypass capacitor Cb.

The CS capacitor has particular influence on the THD+N at high frequencies (above 7 kHz)

and an indirect influence on power supply disturbances. With a value for CS of 1 µF, one can

expect THD+N performance similar to that shown in the datasheet.

In the high frequency region, if CS is lower than 1 µF, then THD+N increases and

disturbances on the power supply rail are less filtered.

On the other hand, if CS is greater than 1 µF, then those disturbances on the power supply

rail are more filtered.

The Cb capacitor has an influence on the THD+N at lower frequencies, but also impacts

PSRR performance (with grounded input and in the lower frequency region).

4.6

Wake-up time tWU

When the standby is released to put the device ON, the bypass capacitor Cb is not charged

immediately. Because Cb is directly linked to the bias of the amplifier, the bias will not work

properly until the Cb voltage is correct. The time to reach this voltage is called the wake-up

time or tWU and is specified in Table 4 on page 5, with Cb=1 µF. During the wake-up phase,

the TS4995 gain is close to zero. After the wake-up time, the gain is released and set to its

nominal value.

If Cb has a value different from 1 µF, then refer to the graph in Figure 57 to establish the

corresponding wake-up time.

Figure 57.

Startup time vs. bypass capacitor

0.00.4

0.81.2

1.62.0

Tamb=25

°C

Vcc=2.6V

Vcc=3.3V

Vcc=5V

Bypass Capacitor Cb (

μF)

TS4995 Datasheet(PDF) 20 Page - STMicroelectronics