TS4909IQT datasheet(27/32 Pages) STMICROELECTRONICS

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TS4909

Application information

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4.6

Wake-up time

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

immediately. As Cb is directly linked to the bias of the amplifier, the bias will not work

properly until the Cb voltage is correct. The time to reach this voltage plus a time delay of

40ms (pop precaution) is called the wake-up time or tWU. It is specified in the electrical

characteristics tables with Cb=1µF (see Section 3: Electrical characteristics on page 5).

If Cb has a value other than 1µF, you can calculate tWU 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 the Cb voltage is equal to 0 V. If the Cb voltage is not equal 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 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 40ms. To follow this

rule, the equivalent input constant time (RinCin) should be less then 8ms:

τ in = Rin xCin <0.008 s

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

20dB.

2.5

⋅

0.042

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

[ms;

μF ]

2.5

⋅

0.417

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

[ms;

μF ]

012

345

100

150

200

250

300

350

AMB

=25°C

Phantom Ground

(

μF)

Single Ended

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