TLE 4271-2
Data Sheet 11 Rev. 2.7, 2007-06-25
Application Description
The IC regulates an input voltage in the range of 6 V <
V
I
< 40 V to V
Qnom
= 5.0 V. Up to
26 V it produces a regulated output current of more than 550 mA. Above 26 V the save-
operating-area protection allows operation up to 36 V with a regulated output current of
more than 300 mA. Overvoltage protection limits operation at 42 V. The overvoltage
protection hysteresis restores operation if the input voltage has dropped below 36 V. The
IC can be switched off via the inhibit input, which causes the quiescent current to drop
below 10 µA. A reset signal is generated for an output voltage of
V
Q
< 4.5 V. The
watchdog circuit monitors a connected controller. If there is no positive-going edge at the
watchdog input within a fixed time, the reset output is set to low. The delay for power-on
reset and the maximum permitted watchdog-pulse period can be set externally with a
capacitor.
Design Notes for External Components
An input capacitor
C
I
is necessary for compensation of line influences. The resonant
circuit consisting of lead inductance and input capacitance can be damped by a resistor
of approx. 1 Ω in series with
C
I
. An output capacitor C
Q
is necessary for the stability of
the regulating circuit. Stability is guaranteed at values of
C
Q
≥ 22 µF and an ESR of
<3Ω.
Reset Circuitry
If the output voltage decreases below 4.5 V, an external capacitor
C
D
on pin D will be
discharged by the reset generator. If the voltage on this capacitor drops below
V
DRL
, a
reset signal is generated on pin RO, i.e. reset output is set low. If the output voltage rises
above the reset threshold,
C
D
will be charged with constant current. After the power-on-
reset time the voltage on the capacitor reaches
V
DU
and the reset output will be set high
again. The value of the power-on-reset time can be set within a wide range depending
of the capacitance of
C
D
.
Reset Timing
The power-on reset delay time is defined by the charging time of an external capacitor
C
d
which can be calculated as follows:
t
D
= C
D
× ∆V/I
D
(1)
Definitions:
•
C
D
= delay capacitor
•
t
D
= reset delay time
•
I
D
= charge current, typical 14 µA
• ∆
V = V
UD
, typical 1.8 V
•
V
UD
= upper delay timing threshold at C
D
for reset delay time
