TDA8950
NXP Semiconductors
2 × 150 W class-D power amplifier
TFB is specified at the temperature value Tact(th_fold) where the closed loop voltage gain is
reduced with 6 dB. The range of the TFB is:
T
act(th_fold) − 5 °C < Tact(th_fold) < Tact(th_prot).
For the TDA8950 the value of Tact(th_fold) is about +153 °C. For more details see: Table 7.
8.3.1.2 OverTemperature Protection (OTP)
If, despite the TFB function, the junction temperature Tj of the TDA8950 continues rising
and exceeds the threshold Tact(th_prot) the amplifier will shutdown immediately. The
amplifier resumes switching approximately 100 ms after the temperature drops below
Tact(th_prot)
.
In Figure 6 the thermal behavior is visualized.
Gain
(dB)
30 dB
24 dB
0 dB
T
T (°C)
j
(T
− 5°C)
act(th_prot)
act(th_fold)
T
act(th_fold)
1
2
3
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(1) Duty cycle of PWM output modulated according audio input signal.
(2) Duty cycle of PWM output reduced due to TFB.
(3) Amplifier is switched off due to OTP.
Fig 6. Behavior of TFB and OTP
8.3.2 OverCurrent Protection (OCP)
If a short-circuit is applied to one of the demodulated outputs of the amplifier, the OCP will
detect this. If the output current exceeds the maximum of 9.2 A, it is automatically limited
to its maximum value by the OCP protection circuit. The amplifier outputs remain
switching (the amplifier is NOT shut-down completely). If the active current limiting
continues longer than time τ, the TDA8950 shuts down. Activation of current limiting and
the triggering of the OCP are observed at pin PROT.
The amplifier can distinguish between an impedance drop of the loudspeaker and a
low-ohmic short-circuit across the load. In the TDA8950 the impedance threshold (Zth)
depends on the supply voltage used.
When a short-circuit is made across the load, causing the impedance to drop below the
threshold level (<Zth), the amplifier is switched off completely and, after a time of 100 ms,
it will try to restart. If the short-circuit condition is still present after this time, the cycle will
be repeated. The average dissipation will be low because of this low duty cycle.
TDA8950_1
© NXP B.V. 2008. All rights reserved.
Preliminary data sheet
Rev. 01 — 9 September 2008
9 of 39
NXP [ NXP ]
