Toshiba TA8266HQ Description And Application Manual page 6

6. Prevention of speaker burning accident
When the direct current resistance between OUT + and OUT − terminal becomes 1 Ω 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 4)
The speaker impedance becomes 1 Ω 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.
Current into a speaker
Less than 4 Ω
Note 4: It is appeared by biased input DC voltage
(for example, large leakage of the input capacitor, short-circuit between copper patterns of PCB.)
(In Case of Rare Short Circuit of Speaker)
↓
↓
Operating point of protector
About 1 Ω
Figure 9
6
Speaker impedance
4 Ω
TA8266HQ
2006-04-28