TS488IQT datasheet(25/32 Pages) STMICROELECTRONICS

25 / 32 page

TS488-TS489

Application information

25/32

4.5

Gain setting

In the flat frequency response region (with no effect from Cin, Cout, Cfeed), the output voltage

is:

The gain AV is:

4.6

Decoupling of the circuit

Two capacitors are needed to properly bypass the TS488 (TS489), a power supply capacitor

Cs and a bias voltage bypass capacitor Cb.

Cs 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 Cs 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 Cs is higher than 1µF, the disturbances on the power supply rail

are more filtered.

Cb 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 Cb is lower than 1µF, the THD+N improves and the PSRR worsens.

■ If Cb is higher than 1µF, the benefit on the THD+N and PSRR is small.

Note:

The input capacitor Cin also has a significant effect on the PSRR at lower frequencies. The

lower the value of Cin, the higher the PSRR.

4.7

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

OUT

feed

--------------

–

⎝⎠

⎛⎞

⋅

feed

--------------

–

25K

600K

Vin1

BYPASS

Vin2

Vout1

Vout2

GND

TS488/9

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