TDA8922B Datasheet, PDF(9/32 Page) NXP Semiconductors

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TDA8922B Datasheet, PDF (9/32 Pages) NXP Semiconductors – 2 X 50 W class-D power amplifier

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Philips Semiconductors

TDA8922B

2 Ã 50 W class-D power ampliï¬er

In case of an impedance drop (e.g. due to dynamic behavior of the loudspeaker) the same

protection will be activated; the maximum output current is again limited to 5 A, but the

ampliï¬er will NOT switch-off completely (thus preventing audio holes from occurring).

Result will be a clipping output signal without any artefacts.

See also Section 13.6 for more information on this maximum output current limiting

feature.

8.3.3 Window Protection (WP)

During the start-up sequence, when pin MODE is switched from standby to mute, the

conditions at the output terminals of the power stage are checked. In the event of a

short-circuit at one of the output terminals to VDD or VSS the start-up procedure is

interrupted and the system waits for open-circuit outputs. Because the test is done before

enabling the power stages, no large currents will ï¬ow in the event of a short-circuit. This

system is called Window Protection (WP) and protects for short-circuits at both sides of

the output ï¬lter to both supply lines. When there is a short-circuit from the power PWM

output of the power stage to one of the supply lines (before the demodulation ï¬lter) it will

also be detected by the start-up safety test. Practical use of this test feature can be found

in detection of short-circuits on the printed-circuit board.

Remark: This test is operational during (every) start-up sequence at a transition between

Standby and Mute mode. However when the ampliï¬er is completely shut-down due to

activation of the OverCurrent Protection (OCP) because a short to one of the supply lines

is made, then during restart (after 100 ms) the window protection will be activated. As a

result the ampliï¬er will not start-up until the short to the supply lines is removed.

8.3.4 Supply voltage protections

If the supply voltage drops below Â±12.5 V, the UnderVoltage Protection (UVP) circuit is

activated and the system will shut-down correctly. If the internal clock is used, this

switch-off will be silent and without pop noise. When the supply voltage rises above the

threshold level, the system is restarted again after 100 ms. If the supply voltage exceeds

Â±33 V the OverVoltage Protection (OVP) circuit is activated and the power stages will

shut-down. It is re-enabled as soon as the supply voltage drops below the threshold level.

So in this case no timer of 100 ms is started.

An additional UnBalance Protection (UBP) circuit compares the positive analog (VDDA)

and the negative analog (VSSA) supply voltages and is triggered if the voltage difference

between them exceeds a certain level. This level depends on the sum of both supply

voltages. An expression for the unbalanced threshold level is as follows:

Vth(ub) â 0.15 Ã (VDDA + VSSA).

When the supply voltage difference drops below the threshold level, the system is

restarted again after 100 ms.

Example: With a symmetrical supply of Â±30 V, the protection circuit will be triggered if the

unbalance exceeds approximately 9 V; see also Section 13.7.

In Table 4 an overview is given of all protections and the effect on the output signal.

9397 750 13357

Preliminary data sheet

Rev. 01 â 1 October 2004

9 of 32

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