TS4909

Application information

Doc ID 11972 Rev 9

29/35

Sample calculation

With R

in

=20k

Ω and F

CL

= 20 Hz and a -3 db low cut-off frequency, C

in

=398 nF.

Therefore, C

in

= 390 nF with standard values which gives a lower cut-off frequency equal to

20.4 Hz.

In this case:

τ

in =

R

in

xC

in

=7.8 ms

This value is sufficient with regard to the previous formula, so we can state that the pop will

be imperceptible.

Connecting the headphones

In general, the headphones are connected using a jack connector. To prevent pop in the

headphones while plugging in the jack, a pulldown resistor should be connected in parallel

with each headphone output. This allows the capacitors C

out

to be charged even when no

headphones are plugged in.

A resistor of 1 k

Ω is high enough to be a negligible load, and low enough to charge the

capacitors C

out

in less than one second.

4.8

Standby mode

When the TS4909 is in standby mode, the time required to put the output stages

(V

out1

, V

out2

and V

out3

) into a high impedance state with reference to ground, and the

internal circuitry in standby mode, is a few microseconds.

Figure 83. Internal equivalent circuit schematics of the TS4909 in standby mode

25K

25K

1M

1M

Vin1

BYPASS

Vin2

Vout1

Vout2

GND

Vout3