TS4995 Datasheet, PDF (20/26 Pages) STMicroelectronics – 1.2 W fully differential audio power amplifier with selectable standby and 6 dB fixed gain

Application information
TS4995
4.5
Decoupling of the circuit
Two capacitors are needed to correctly bypass the TS4995: a power supply bypass
capacitor C_S and a bias voltage bypass capacitor C_b.
The C_S capacitor has particular influence on the THD+N at high frequencies (above 7 kHz)
and an indirect influence on power supply disturbances. With a value for C_S of 1 µF, one can
expect THD+N performance similar to that shown in the datasheet.
In the high frequency region, if C_S is lower than 1 µF, then THD+N increases and
disturbances on the power supply rail are less filtered.
On the other hand, if C_S is greater than 1 µF, then those disturbances on the power supply
rail are more filtered.
The C_b 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).
4.6
Wake-up time t_WU
When the standby is released to put the device ON, the bypass capacitor C_b is not charged
immediately. Because C_b is directly linked to the bias of the amplifier, the bias will not work
properly until the C_b voltage is correct. The time to reach this voltage is called the wake-up
time or t_WU and is specified in Table 4 on page 5, with C_b=1 µF. During the wake-up phase,
the TS4995 gain is close to zero. After the wake-up time, the gain is released and set to its
nominal value.
If C_b has a value different from 1 µF, then refer to the graph in Figure 57 to establish the
corresponding wake-up time.
Figure 57. Startup time vs. bypass capacitor
15
Tamb=25°C
Vcc=5V
10
5
Vcc=2.6V
Vcc=3.3V
0
0.0
0.4
0.8
1.2
1.6
2.0
Bypass Capacitor Cb (μF)
20/26