TDA8920C
NXP Semiconductors
2 × 110 W class-D power amplifier
When OCP is activated, the power transistors are turned off. They are turned on again
during the next switching cycle. If the output current is still greater than the OCP threshold,
they will be immediately switched off again. This switching will continue until CPROT is fully
discharged. The amplifier will then be switched off completely and a restart sequence
initiated.
After a fixed period of 100 ms, the amplifier will attempt to switch on again, but will fail if
the output current still exceeds the OCP threshold. The amplifier will continue trying to
switch on every 100 ms. The average power dissipation will be low in this situation
because the duty cycle is low.
Switching the amplifier on and off in this way will generate unwanted ‘audio holes’. This
can be avoided by increasing the value of CPROT (up to 220 pF) to delay amplifier
switch-off. CPROT will also prevent the amplifier switching off due to transient
frequency-dependent impedance drops at the speakers.
The amplifier will switch on, and remain in Operating mode, once the overcurrent
condition has been removed. OCP ensures the TDA8920C amplifier is fully protected
against short-circuit conditions while avoiding audio holes.
Table 4.
Type
Current limiting behavior during low output impedance conditions at different
values of CPROT
VP
(V)
VI (mV, p-p) f (Hz) CPROT PWM output stops
(pF)
Short
Short
Short
(Zth = 0 Ω) (Zth = 0.5 Ω)
(Zth = 1 Ω)
TDA8920C
29.5 500
20
1000 10
20 15
10
yes
yes
yes
yes
no
yes
yes
yes
no
OVP[1]
no
OVP[1]
no
1000 15
1000 220
no
no
[1] OVP can be triggered by supply pumping; see Section 13.6.
8.3.3 Window Protection (WP)
Window Protection (WP) checks the conditions at the output terminals of the power stage
and is activated:
• During the start-up sequence, when the TDA8920C is switching from Standby to
Mute.
Start-up will be interrupted If a short-circuit is detected between one of the output
terminals and pin VDDP1/VDDP2 or VSSP1/VSSP2. The TDA8920C will wait until the
short-circuit to the supply lines has been removed before resuming start-up. The short
circuit will not generate large currents because the short-circuit check is carried out
before the power stages are enabled.
• When the amplifier is shut down completely because the OCP circuit has detected a
short circuit to one of the supply lines.
WP will be activated when the amplifier attempts to restart after 100 ms (see
Section 8.3.2). The amplifier will not start-up again until the short circuit to the supply
lines has been removed.
TDA8920C_2
© NXP B.V. 2009. All rights reserved.
Product data sheet
Rev. 02 — 11 June 2009
10 of 39
NXP [ NXP ]
