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TS4984FC Datasheet, PDF (22/30 Pages) STMicroelectronics – 1.2W Stereo Audio Power Amplifier with Active Low Standby Mode
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Application Information
TS4984FC
Note:
● If Cb is higher than 1µF, the benefit on THD+N at lower frequencies is small, but the benefit
to PSRR is substantial.
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
in Figure 65.
Figure 64. Typical wake-up time vs. Cb
Figure 65. Maximum wake-up time vs. Cb
600
Tamb=25°C
500
Vcc=3.3V
400
Vcc=2.6V
300
200
Vcc=5V
100
0
0.1
1
2
3
4
4.7
Bypass Capacitor Cb ( F)
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)
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
Note:
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.
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.
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