TS4990IQT datasheet(21/33 Pages) STMICROELECTRONICS

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TS4990

Application information

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 wake-up time

or tWU and specified in the electrical characteristics tables with Cb =1 µF.

If Cb has a value other than 1 µF, refer to the graph in Figure 61 to establish the wake-up

time.

Figure 61. Typical wake-up time vs. Cb

Due to process tolerances, the maximum value of wake-up time is shown in Figure 62.

Figure 62. Maximum wake-up time vs. Cb

Note:

The bypass capacitor Cb also has a typical tolerance of +/-20%. To calculate the wake-up

time with this tolerance, refer to the graph above (considering for example for Cb=1 µF in

the range of 0.8 µF

 C

b 1.2 µF).

4.7

Standby time

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

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

mode, the bypass pin and Vin pin are short-circuited to ground by internal switches. This

allows a quick discharge of Cb and Cin capacitors.

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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