TDF8544
NXP Semiconductors
I2C-bus controlled 4 50 W power amplifier
PMOS
IRF5305
3
V
pulse
(1)
5
7
2200 μF
9
C
17
19
21
23
buffer
116 mF
V
P
R
S
Loss-of-V tester
DUT in application
P
001aao146
(1) Amplifier output stage.
Fig 8. Test circuit for loss-of-VP test
7.4.3 Speaker fault detection
There are two protection features available to prevent damage to the speaker if one side
of the speaker is connected to ground.
• A check for a speaker fault operates during start-up. This is included in the check for a
short to ground; the channel that has the speaker fault is switched off. If the short to
ground bit is set, it can mean either a short to ground or a speaker fault. At start-up it
is difficult to distinguish between a speaker fault and a short to ground. The amplifier
is protected against both, but the speaker fault bit is not always set.
• A check for a speaker fault operates continuously. If a speaker fault is detected, bit D6
in registers DB1 to DB4 are set but the amplifier is not switched off and pin DIAG is
not pulled LOW.
7.4.4 Overvoltage warning and load dump protection
If the battery voltage VP exceeds the maximum value of Vth(ovp), the device switches off
the output stages of the amplifier to protect the output transistors. The overvoltage
pre-warning bit is set when the supply voltage level exceeds the value of VP(ovp)pwarn
.
The functionality of the diagnostic output can be chosen in I2C-bus mode. In this mode the
pre-warning information can become visible at the diagnostic output. In legacy mode, pin
DIAG will not be activated under pre-warning conditions.
Although the amplifier switches off the output stages, the device remains operational
during load dump conditions (maximum value of VP at load dump protection; duration
50 ms, rise time > 2.5 ms). The occurrence of the load dump situation can last for a longer
period of time without damaging the device. Provided that the I2C-bus supply is within the
levels specified, communication with the I2C-bus bus during load dump situations remains
possible and the status of the channel outputs can be read.
TDF8544
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2011. All rights reserved.
Product data sheet
Rev. 2 — 29 August 2011
12 of 54
NXP [ NXP ]
