TA8276H

2002-02-13

6

5.3

Prevention of speaker burning accident (In Case of Rare Short Circuit of Speaker)

When the direct current resistance between OUT + and OUT - terminal becomes 1 W or less and output

current over 4 A flows, this IC makes a protection circuit operate and suppresses the current into a speaker.

This system makes the burning accident of the speaker prevent as below mechanism.

<The guess mechanism of a burning accident of the speaker>

Abnormal output offset voltage (voltage between OUT + and OUT -) over 4 V is made by the external

circuit failure.(Note 1)

¯

The speaker impedance becomes 1 W or less as it is in a rare short circuit condition.

¯

The current more than 4 A flows into the speaker and the speaker is burned.

Note 1: It is appeared by biased input DC voltage

(for example, large leakage of the input capacitor, short-circuit between copper patterns of PCB.)

5.4

Applications

And when shorting OUT + to OUT -, “L” and “H” are switched according to an input signal.

Therefore, it is possible to judge how the power IC condition is if a micro-controller detects the

25pin voltage that is smoothed out with LPF.

It is recommend that the threshold voltage (Vth) is set up as higher as possible because output level

of LPF is changed according to an input signal.

(for example, Vth is set up to 4 V if 25pin is pulled up to 5 V line.)

Current into a speaker

Speaker impedance

Less than 4

W

Figure 9

About 1

W

4

W

Operating point of protector

Output voltage of L.P.F.

Output power

5 V

Figure 10

Operating point of protector