Application information

TS4909

28/35

Doc ID 11972 Rev 9

4.6

Wake-up time

When the standby is released to turn the device ON, the bypass capacitor C

b

is charged

immediately. As C

b

is directly linked to the bias of the amplifier, the bias will not work

properly until the C

b

voltage is correct. The time to reach this voltage plus a time delay of

40 ms (pop precaution) is called the wake-up time or t

WU

. It is specified in the electrical

characteristics tables with C

b

=1 μF (see

Section 3: Electrical characteristics on page 7).

If C

b

has a value other than 1 μF, you can calculate t

WU

by using the following formulas, or

read it directly from the graph in

Figure 82.

Single-ended configuration:

Phantom ground configuration:

Figure 82. Typical wake-up time vs. bypass capacitance

Note:

It is assumed that the C

b voltage is equal to 0 V. If the

C

b voltage is not equal to 0 V, the

wake-up time is lower.

4.7

Pop performance

Pop performance in the phantom ground configuration is closely linked with the size of the

input capacitor C

in

. The size of C

in

is dependent on the lower cut-off frequency and PSRR

values requested.

In order to reach low pop, C

in

must be charged to V

CC

/2 in less than 40 ms. To follow this

rule, the equivalent input constant time (R

in

C

in

) should be less then 8 ms.

τ

in =

R

in

xC

in

<0.008 s

By following the previous rules, the TS4909 can reach low pop even with a high gain such

as 20 dB.

t

WU

Cb

2.5

⋅

0.042

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

40

[ms;

μF ]

+

=

t

WU

Cb

2.5

⋅

0.417

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

40

[ms;

μF ]

+

=

012

345

0

50

100

150

200

250

300

350

T

AMB

=2 5° C

P hantom G round

Cb (μF)

S ingle E nded