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Preliminary data sheet

Rev. 01 — 1 October 2004

10 of 34

Philips Semiconductors

TDA8920B

2

× 100 W class-D power amplifier

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

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

enabling the power stages, no large currents will flow 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 filter 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 filter) 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 amplifier 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 amplifier 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

±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

±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.

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:

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

restarted again after 100 ms.

Example: With a symmetrical supply of

±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.

[1]

Hysteresis of 20 degrees will influence restart timing depending on heatsink size.

Table 4:

Overview protections TDA8920B

Protection name

Complete shut-down

Restart directly

Restart every 100 ms

OTP

Y

Y [1]

N [1]

OCP

N [2]

Y [2]

N [2]

WP

Y [3]

YN

UVP

Y

N

Y

OVP

YYN

UBP

Y

N

Y