TS4984FC datasheet(22/30 Pages) STMICROELECTRONICS

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Application Information

TS4984FC

22/30

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If Cb is higher than 1µF, the benefit on THD+N at lower frequencies is small, but the benefit

to PSRR is substantial.

Note:

The TS4984FC has two BYPASS pins. Cb can be connected equally to pin C5 or to pin C1.

These pins are internally connected. Connecting pin C5 and pin C1 together by an external

wire is optional.

Cin has a non-negligible effect on PSRR at lower frequencies. The lower the value of Cin, the

higher the PSRR.

4.6

Wake-up time, twu

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

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

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

or twu and specified in the tables in Chapter 3: Electrical Characteristics with Cb = 1µF.

If Cb has a value other than 1µF, please refer to the graph in Figure 64 to establish the wake-up

time value.

Due to process tolerances, the maximum value of wake-up time could be establish by the graph

Figure 65.

Note:

Bypass capacitor Cb as also a tolerance of typically +/-20%. To calculate the wake-up time with

this tolerance, refer to the previous graph (considering for example for Cb = 1µF in the range of

0.8µF

≤ 1µF ≤ 1.2µF).

4.7

Shutdown time

When the standby command is set, the time required to put the two output stages in high

impedance and the internal circuitry in shutdown mode is a few microseconds.

Note:

In shutdown mode, Bypass pin and Vin- pin are short-circuited to ground by internal switches.

This allows for the quick discharge of the Cb and Cin capacitors.

Figure 64. Typical wake-up time vs. Cb

Figure 65. Maximum wake-up time vs. Cb

100

200

300

400

500

600

4.7

0.1

Tamb=25

°C

Vcc=2.6V

Vcc=3.3V

Vcc=5V

Bypass Capacitor Cb ( F)

100

200

300

400

500

600

Tamb=25

°C

4.7

0.1

Vcc=5V

Vcc=3.3V

Vcc=2.6V

Bypass Capacitor Cb ( F)

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