TLE 4270
Application Description
The IC regulates an input voltage in the range of 5.5 V
<
V
I
<
36 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. A reset signal is generated for an output voltage of
V
Q
<
4.5 V. The delay for
power-on reset 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
<
3
Ω.
Circuit Description
The control amplifier compares a reference voltage, which is kept highly accurate by
resistance adjustment, to a voltage that is proportional to the output voltage and drives
the base of a series transistor via a buffer. Saturation control as a function of the load
current prevents any over-saturation of the power element.
If the output voltage decreases below 4.5 V, an external capacitor
C
D
on pin 4 (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 2 (RO), i.e. reset output is set low. If the output voltage
rises above 4.5 V,
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
.
The IC also incorporates a number of internal circuits for protection against:
•
•
•
•
Overload
Overvoltage
Overtemperature
Reverse polarity
Semiconductor Group
3
1998-11-01
INFINEON [ INFINEON TECHNOLOGIES AG ]
