TS488 Datasheet, PDF (25/32 Pages) STMicroelectronics – Pop-free 120mW stereo headphone amplifier

TS488-TS489
Application information
4.5
Gain setting
In the flat frequency response region (with no effect from C_in, C_out, C_feed), the output voltage
is:
V_OUT = V_IN ⋅
⎛
⎝
–
R_{----R-f--e-i--ne---d-⎠⎞}
= V_IN ⋅
A_V
The gain A_V is:
A_V
=
–^R-----^f--^e---^e---^d-
R_in
4.6
Note:
4.7
Decoupling of the circuit
Two capacitors are needed to properly bypass the TS488 (TS489), a power supply capacitor
C_s and a bias voltage bypass capacitor C_b.
C_s has a strong influence on the THD+N in the high frequency range (above 7kHz) and
indirectly on the power supply disturbances. With 1µF, you can expect THD+N performance
to be similar to the one shown in the datasheet. If C_s is lower than 1µF, the THD+N
increases in the higher frequencies and disturbances on the power supply rail are less
filtered. On the contrary, if C_s is higher than 1µF, the disturbances on the power supply rail
are more filtered.
C_b has an influence on the THD+N in the low frequency range. Its value is critical on the
PSRR with grounded inputs in the lower frequencies:
■ If C_b is lower than 1µF, the THD+N improves and the PSRR worsens.
■ If C_b is higher than 1µF, the benefit on the THD+N and PSRR is small.
The input capacitor C_in also has a significant effect on the PSRR at lower frequencies. The
lower the value of C_in, the higher the PSRR.
Standby mode
When the standby mode is activated an internal circuit of the TS488 (TS489) is charged
(see Figure 82). A time required to change the internal circuit is a few microseconds.
Figure 82. Internal equivalent schematic of the TS488 (TS489) in standby mode
TS488/9
Vin1
Vout1
25K
600K
BYPASS
GND
Vin2
25K
600K
Vout2
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