TDA8922C
NXP Semiconductors
2 × 75 W class-D power amplifier
TFB is specified at the thermal foldback activation temperature Tact(th_fold) where the
closed-loop voltage gain is reduced by 6 dB. The TFB range is:
T
act(th_fold) − 5 °C < Tact(th_fold) < Tact(th_prot)
The value of Tact(th_fold) for the TDA8922C is approximately 153 °C; see Table 8 for more
details.
8.3.1.2 OverTemperature Protection (OTP)
If TFB fails to stabilize the temperature and the junction temperature continues to rise, the
amplifier will shut down as soon as the temperature reaches the thermal protection
activation threshold, Tact(th_prot). The amplifier will resume switching approximately 100 ms
after the temperature drops below Tact(th_prot)
.
The thermal behavior is illustrated in Figure 6.
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
001aah656
(1) Duty cycle of PWM output modulated according to the 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)
In order to guarantee the robustness of the TDA8922C, the maximum output current
delivered at the output stages is limited. OCP is built in for each output power switch.
OCP is activated when the current in one of the power transistors exceeds the OCP
threshold (IORM = 6 A) due, for example, to a short-circuit to a supply line or across the
load.
The TDA8922C amplifier distinguishes between low-ohmic short-circuit conditions and
other overcurrent conditions such as a dynamic impedance drop at the loudspeakers. The
impedance threshold (Zth) depends on the supply voltage.
How the amplifier reacts to a short circuit depends on the short-circuit impedance:
• Short-circuit impedance > Zth: the amplifier limits the maximum output current to IORM
but the amplifier does not shut down the PWM outputs. Effectively, this results in a
clipped output signal across the load (behavior very similar to voltage clipping).
TDA8922C_1
© NXP B.V. 2009. All rights reserved.
Product data sheet
Rev. 01 — 7 September 2009
9 of 40
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