Overtemperature Protection (Otp); Overcurrent Protection (Ocp) - Philips TDA8950 Product Data Sheet

NXP Semiconductors

8.3.1.2 OverTemperature Protection (OTP)

8.3.2 OverCurrent Protection (OCP)

TDA8950_2
Product data sheet
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, T
after the temperature drops below T
The thermal behavior is illustrated in
30 dB
24 dB
(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
In order to guarantee the robustness of the TDA8950, the maximum output current that
can be 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 (I = 9.2 A) due, for example, to a short-circuit to a supply line or across the
ORM
load.
The TDA8950 amplifier distinguishes between low-ohmic short-circuit conditions and
other overcurrent conditions such as a dynamic impedance drop at the loudspeaker. The
impedance threshold (Z
How the amplifier reacts to a short circuit depends on the short-circuit impedance:
•
Short-circuit impedance > Z
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).
•
Short-circuit impedance < Z
and at the same time discharges the capacitor on pin PROT. When C
discharged, the amplifier shuts down completely and an internal timer is started.
The value of the protection capacitor (C
10 pF and 220 pF (typically 47 pF). While OCP is activated, an internal current source is
enabled that will discharge C
. The amplifier will resume switching approximately 100 ms
act(th_prot)
act(th_prot)
Figure
Gain
(dB)
0 dB
(T 5 C)
act(th_fold)
1
) depends on the supply voltage.
th
: the amplifier limits the maximum output current to I
th
: the amplifier limits the maximum output current to I
th
PROT
.
PROT
Rev. 02 — 11 June 2009
2 150 W class-D power amplifier
.
6.
T T ( C)
act(th_prot) j
T
act(th_fold)
2 3
001aah656
) connected to pin PROT can be between
TDA8950
ORM
ORM
is fully
PROT
© NXP B.V. 2009. All rights reserved.
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