STA321 datasheet(62/157 Pages) STMICROELECTRONICS

62 / 157 page

CMOS power stage

STA321

62/157

Doc ID 15351 Rev 3

At the appropriate time the two pop-free resistors allow the bypass capacitor to be charged

to VCCx / 2. The STA321 generates automatically the bridge start-up and switch-off

sequence to provide the correct charging. The time TT in Figure 38 below is set using

registers CBTTF0-1 and CBTTP0-1. TT must be chosen for the specific application

depending on the decoupling capacitor, load and power supply.

After powerdown is applied again the decoupling capacitor discharges slowly due to

capacitor leakage.

The analog pop-free implementation cannot be used with the digital pfStart implementation

Both analog and digital pop-free features must be disabled if binary headphone modulation

is used.

Figure 38.

Analog pop-free start-up and switch-off sequence

The CMOS bridge circuit includes over-current protection. The FAULT signal indicates to the

output the status of the over-current condition due to a short circuit. The over-current

thresholds detected by the CMOS bridge are fixed at 1.8 A.

Table 26.

Logic circuit at bridge input

Powerdown

Tristate

PopFree

Pop-free resistors

Bridge status

000Disconnected

3-state

001Disconnected

3-state

101Connected

3-state

111Disconnected

110Disconnected

Powerdown

PFE

Tristate

V(capacitor)

Vcc / 2

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