NXP Semiconductors
TFA9896
Boosted audio system with adaptive sound maximizer and speaker protection
TFA9896 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2016. All rights reserved.
Product short data sheet Rev. 1 — 22 December 2016
COMPANY PUBLIC 7 / 22
8.1 Protection mechanisms
The following protection circuits are included in the TFA9896:
• OverTemperature Protection (OTP)
• OverVoltage Protection (OVP)
• UnderVoltage Protection (UVP)
• OverCurrent Protection (OCP)
The reaction of the device to fault conditions differs depending on the protection circuit
involved. The status of these protection circuits can be monitored via the relevant status
bits in the System status register, which can be configured to generate interrupts.
8.1.1 OverTemperature Protection (OTP)
OTP prevents heat damage to the TFA9896. It is triggered when the junction temperature
exceeds T
act(th_prot)
. The output stages are set floating. OTP is cleared automatically via
an internal timer (approximately 200 ms), after which the output stages start to operate
normally again. The overtemperature status can be monitored via the I
2
C-bus.
8.1.2 Supply voltage protection (UVP and OVP)
If V
BAT
drops below the undervoltage protection threshold, V
P(uvp)
, UVP is activated,
setting the outputs floating. The system is restarted approximately 200 ms after the
supply voltage rises above V
P(uvp)
again.
If the power supply voltage (V
DDP
) rises above the overvoltage protection threshold,
V
P(ovp)
, OVP is activated, setting the booster to Follower mode. The power stages are
re-enabled as soon as the supply voltage drops below V
P(ovp)
again. The system will be
restarted after approximately 200 ms. The undervoltage and overvoltage status can be
monitored via the I
2
C-bus.
8.1.3 OverCurrent Protection (OCP)
OCP detects a short circuit across the load or between one of the amplifier outputs and
one of the supply lines. If the output current exceeds the overcurrent protection threshold
(I
O(ocp)
), it is limited to I
O(ocp)
while the amplifier outputs are switching (the amplifier is not
powered down completely). The amplifier can distinguish between an impedance drop
at the loudspeaker and a low-ohmic short circuit across the load or to one of the supply
lines. The impedance threshold depends on which supply voltage is being used:
• In the event of a short circuit across the load or a short to one of the supply lines, the
audio amplifier is switched off completely. It will try to restart again after approximately
200 ms at a sample rate, f
s
, of 48 kHz. If the short-circuit condition is still present after
this time, this cycle will be repeated. Average dissipation is low because of the short
duty cycle.
• The same protection mechanism is activated in the event of an impedance drop (e.g.
due to dynamic behavior of the loudspeaker). The maximum output current is again
limited to I
O(ocp)
, but the amplifier does not switch off completely (preventing audio
holes from occurring). The result is a clipped output signal without artifacts.
