TS4990 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TS4990' PDF : 33 Pages View PDF
TS4990
Application information
4.6
Note:
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
600
Tamb=25°C
500
400
Vcc=2.6V
300
Vcc=3.3V
200
Vcc=5V
100
0
0.1
1
2
3
4
4.7
Bypass Capacitor Cb ( F)
Due to process tolerances, the maximum value of wake-up time is shown in Figure 62.
Figure 62. Maximum wake-up time vs. Cb
600 Tamb=25°C
500
400
Vcc=2.6V
Vcc=3.3V
300
200
Vcc=5V
100
0
0.1
1
2
3
4
4.7
Bypass Capacitor Cb ( F)
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≤Cb≤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.
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