TDF8553J NXP Semiconductors, TDF8553J Datasheet - Page 11

• Manufacturer Part Number: TDF8553J
• Description: I2C-bus controlled 4 X 50 Watt power amplifier and multiple voltage regulator
• Manufacturer: NXP Semiconductors

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TDF8553J_1
Objective data sheet
8.5.7.3 Load detection procedure
8.5.8 Low headroom protection
The normal DC output voltage of the amplifier is set to half the supply voltage and is
related to the voltage on pin SVR. An external capacitor is connected to pin SVR to
suppress power supply ripple. If the supply voltage drops (at vehicle engine start), the DC
output voltage will follow slowly due to the affect of the SVR capacitor.
The headroom voltage is the voltage required for correct operation of the amplifier and is
defined as the voltage difference between the level of the DC output voltage before the V
voltage drop and the level of V
At a certain supply voltage drop, the headroom voltage will be insufficient for correct
operation of the amplifier. To prevent unwanted audible noises at the output, the
headroom protection mode will be activated (see
capacitors connected to pins SVR and ACGND to increase the headroom voltage.
1. At start-up, enable the AC or DC-load detection by setting D1 of instruction byte IB1 to
2. After 250 ms the DC load is detected and the mute is released. This is inaudible and
3. When the amplifier start-up cycle is completed (after 1.5 s), apply an AC signal to the
4. After at least 3 periods of the input signal, the load status can be checked by reading
Fig 3.
logic 1.
can be implemented each time the IC is powered on.
input, and DC-load bits D5 of each data byte should be read and stored by the
microcontroller.
AC-detect bits D4 of each data byte.
The AC-load peak current counter can be reset by setting bit D1 of instruction
byte IB1 to logic 0 and then to logic 1. Note that this will also reset the DC-load
detection bits D5 in each data byte.
(1) I
(2) I
Tolerance of AC-load detection as a function of output voltage
oM
oM
= < 150 mA.
= > 550 mA.
Rev. 01 — 3 December 2008
( )
Z
L
10
10
1
2
0
4
P
50 Watt power amplifier and multiple voltage regulator
after the voltage drop (see
no load present
2.5
undefined
5
load present
Figure
(1)
(2)
7.5
V
4). This protection discharges the
001aai691
oM
(V)
Figure
10
4).
TDF8553J
© NXP B.V. 2008. All rights reserved.
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