TS487-1 datasheet(28/31 Pages) STMICROELECTRONICS

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TS486-TS487

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and for various values of the input resistor RIN .

The input resistance of the fixed gain version is

typically 20k

Ω.

The following curve shows the limits of the roll off

frequency depending on the min. and max. values

of Rin:

LOW FREQUENCY ROLL OFF WITH OUTPUT

CAPACITORS

The DC voltage on the outputs of the TS486/487

is blocked by the output capacitors COUT1 and

COUT2 . Each output capacitor COUT in series with

the resistance of the load RL is equivalent to a first

order high pass filter.

Assuming that Fmin is the lowest frequency to be

amplified (with a 3dB attenuation), the minimum

value of COUT is:

COUT > 1 / (2*π*Fmin*RL)

The following curve gives directly the low roll-off

frequency versus the output capacitor COUT in µF

and for the two typical 16

Ω and 32Ω impedances:

DECOUPLING CAPACITOR CB

The internal bias voltage at Vcc/2 is decoupled

with the external capacitor CB.

The TS486 and TS487 have a specified Power

Supply Rejection Ratio parameter with CB = 1µF.

A higher value of CB improves the PSRR, for

example, a 4.7µF improves the PSRR by 15dB at

200Hz (please, refer to fig. 76 "PSRR vs Bypass

Capacitor").

POP PRECAUTIONS

Generally headphones are connected using a

connector as a jack. To prevent a pop in the

headphones when plugged in the jack, a resistor

should be

connected in

parallel with

each

headphone output. This allows the capacitors

Cout to be charged even when no headphone is

plugged.

A resistor of 1 k

Ω is high enough to be a negligible

load, and low enough to charge the capacitors

Cout in less than one second.

0.01

0.1

100

1000

Rin = 100k

Ω

Rin = 20k

Ω and

fixed gain versions

Rin = 10k

Ω

Rin = 1k

Ω

Cin (µF)

Ω

100

1000

10000

100

1000

RL = 16

Ω

RL = 32

Ω

OUT

( F)

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