
TLE 4269
Semiconductor Group 5 1998-11-01
Circuit Description
The control amplifier compares a reference voltage, made highly accurate by resistance
balancing, with a voltage proportional to the output voltage and drives the base of the
series PNP transistor via a buffer. Saturation control as a function of the load current
prevents any over-saturation of the power element.
In the reset generator block a comparator compares a reference voltage independent of
the input voltage with the scaled-down output voltage. If the output voltage reaches 4.6 V
the reset delay capacitor is discharged and the reset output is set to low. This low is
guaranteed down to an output voltage of 1 V. As the output voltage increases again,
from 4.6 V onward the reset delay capacitor is charged with constant current. When the
capacitor voltage reaches the upper switching threshold VdT, the reset returns to high. By
choosing the value of this capacitor, the reset delay time can be selected over a wide
range. With the rese t t hresh old in put RE it is po ss ible to lo we r the reset thres hol d Vrt. If
pin RE is connected to pin Q via a voltage divider, for example, the reset condition is
reached when this voltage is decreased below the switching threshold Vre of 1.35 V.
Another comparator compares the signal of the pin SI, normally fed by a voltage divider
from the input voltage, with the reference and gives an early warning on the pin SO. It is
also possible to superwise an other voltage e.g. of a second regulator, or to build a
watchdog circuit with few external components.
Application Description
The input capacitor CI is necessary for compensating line influences. Using a resistor of
approx. 1 Ω in series with CI, the oscillating circuit consisting of input inductivity and input
ca pacita nce c an be damp ed. Th e out put c apac itor CQ is necessary for the stability of the
regulating circuit. Stability is guaranteed at values ≥10 µF and an ESR ≤10 Ω within the
operating te mperature range. Fo r small toleranc es of the rese t delay the spread of the
capacitance of the delay capacitor and its temperature coefficient should be noted.