If Cb has a value other than 1 µF, tWU can be calculated by applying the following formulas or can be read directly

from Figure 79. Typical wake-up time vs. bypass capacitance

tWU=Cb⋅2.5

0.03125+20ms;μF

(17)

Figure 79. Typical wake-up time vs. bypass capacitance

0

1

2

3

4

5

0

50

100

150

200

250

300

350

400

T

AMB=25°C

Cb (μF)

Note:

It is assumed that the Cb voltage is equal to 0 V. If the Cb voltage is not equal to 0 V, the wake-up time is shorter.

5.10

POP performance

Pop performance is closely related to the size of the input capacitor Cin. The size of Cin is dependent on the lower

cut-off frequency and PSRR values requested.

In order to reach low pop, Cin must be charged to VCC/2 in less than 20 ms. To follow this rule, the equivalent

input constant time (RinCin) should be less then 6.7 ms:

tin = Rin x Cin < 0.0067 (s)

Example calculation:

In the typical application schematic Rin is 20 kΩ and Cin is 330 nF. The lower cut-off frequency (-3 db attenuation)

is given by the following formula

FCL= 1

2π⋅Rin⋅Cin

(18)

With the values above, the result is FCL = 25 Hz.

In this case, tin = Rin x Cin=6.6 ms.

This value is sufficient with regard to the previous formula, thus we can state that the pop is imperceptible.

Connecting the headphones

Generally headphones are connected using jack connectors. To prevent a pop in the headphones when plugging

in the jack, a pull-down resistor should be connected in parallel with each headphone output. This allows the

capacitors Cout to be charged even when the headphones are not plugged in.

Pull-down resistors with a value of 1 kΩ are high enough to be a negligible load, and low enough to charge the

capacitors Cout in less than one second.

Note:

The pop&click reduction circuitry works properly only when both channels have the same value for the external

components Cin, Cout, Rload and Rpulldown.

TS488

POP performance

DS4579 - Rev 8

page 24/32