TDF8553J NXP Semiconductors, TDF8553J Datasheet - Page 13

• 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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NXP Semiconductors
TDF8553J_1
Objective data sheet
8.6.3 Backup function
8.6.4 Power switches
The backup function is implemented by a switch function, which behaves like an ideal
diode between pins V
the current flowing through it. The backup function supplies regulator 2 during brief
periods when no supply voltage is present on pin V
be connected to pin BUCAP and ground. When the supply voltage is present on pin V
this capacitor will be charged to a level of V
from pin V
calculated using the formula:
Example: V
C
When an overvoltage condition occurs, the voltage on pin BUCAP is limited to
approximately 24 V; see
There are two power switches that provide an unregulated DC voltage output for
amplifiers and an aerial motor respectively. The switches have internal protection for
over-temperature conditions and are activated by setting bits D2 and D3 of instruction
byte IB1 to logic 1.
In the ON state, the switches have a low impedance to the battery voltage. When the
battery voltage is higher than 22 V, the switches are switched off. When the battery
voltage is below 22 V the switches are set to their original condition.
The power switches have built-in surge protection to be able to absorb energy from
switching inductive or capacitive external loads. This surge protection is implemented in
such a way that in case no supply (V
a possible external source connected to a power switch output.
t
backup
Fig 5.
backup
=
= 100 F provides a t
V
Backup capacitor function
t
C
REG2
P
backup
, this charge can then be used to supply regulator 2 for a brief period (t
P
(V)
backup
V
V
P
= 14.4 V, V
=
C
R
backup
L
Rev. 01 — 3 December 2008
P
and BUCAP; the forward voltage of this ideal diode depends on
REG2
Figure
V
-----------------------------------------------
P
4
V
----------------------------------------------- -
–
backup
(voltage on pin REG2) = 3.3 V, R
P
50 Watt power amplifier and multiple voltage regulator
V
V
–
5.
REG2
REG2
V
I
of 321 ms.
REG2
load
P
) is present the supply line will not be charged from
–
0.5
–
t
0.5
backup
V
P
BUCAP
0.3 V. When the supply voltage is absent
P
. It requires an external capacitor to
out of regulation
L
= 1 k and
TDF8553J
© NXP B.V. 2008. All rights reserved.
001aai693
t (s)
backup
13 of 47
P
)