STMicroelectronics 1.2 W fully differential audio power amplifier DEMOTS4995J DEMOTS4995J Data Sheet

20/26

  

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).

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 

, 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 

 to establish the 

corresponding wake-up time.

0.0

0.4

0.8

1.2

1.6

2.0

0

5

10

15

Tamb=25

°

C

Vcc=2.6V

Vcc=3.3V

Vcc=5V

μ