TS489IQT datasheet(26/32 Pages) STMICROELECTRONICS

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Application information

TS488-TS489

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4.8

Wake-up time

When the standby is released to put 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

20ms (pop precaution) is called the wake-up time or tWU; it is specified in the electrical

characteristics table with Cb = 1µF.

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

can be read directly from Figure 83.

Figure 83.

Typical wake-up time vs. bypass capacitance

Note:

It is assumed that the Cb voltage is equal to 0V. If the Cb voltage is not equal to 0V, the

wake-up time is shorter.

4.9

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 20ms. To follow this

rule, the equivalent input constant time (RinCin) should be less then 6.7ms:

τ in = Rin xCin < 0.0067 (s)

Example calculation:

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

(-3db attenuation) is given by the following formula:

2.5

⋅

0.03125

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

[ms;

μF ]

012

345

100

150

200

250

300

350

400

AMB

=25°C

Cb (

μF)

π R

⋅⋅

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