TS4997 datasheet(26/34 Pages) STMICROELECTRONICS

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Application information

TS4997

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

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

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

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

disturbances on the power supply rail are less filtered.

On the other hand, if CS is greater than 1µF, 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).

4.10

Standby control and wake-up time tWU

The TS4997 has two dedicated standby pins (STBYL, STBYR). These pins allow to put

each channel in standby mode or active mode independently. The amplifier is designed to

reach close to zero pop when switching from one mode to the other.

When both channels are in standby (VSTBYL = VSTBYR = GND), the circuit is in shutdown

mode. When at least one of the two standby pins is released to put the device ON, the

bypass capacitor Cb starts to be charged. 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=1µF.

During the wake-up phase, the TS4997 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 1µF, then refer

to the graph in Figure 66 to establish the corresponding wake-up time.

When a channel is set to standby mode, the outputs of this channel are in high impedance

state.

Figure 66.

Typical startup time vs. bypass capacitor

0.00.5

1.01.5

2.02.5

3.03.5

4.04.5

100

Tamb=25

°C

Vcc=2.7V

Vcc=3.3V

Vcc=5V

Bypass Capacitor Cb (

μF)

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