TLE4269 Datasheet, PDF (5/19 Pages) Siemens Semiconductor Group – 5-V Low-Drop Fixed Voltage Regulator

TLE 4269
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 V_dT, 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 reset threshold input RE it is possible to lower the reset threshold V_rt. 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 V_re 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 C_I is necessary for compensating line influences. Using a resistor of
approx. 1 Ω in series with C_I, the oscillating circuit consisting of input inductivity and input
capacitance can be damped. The output capacitor C_Q is necessary for the stability of the
regulating circuit. Stability is guaranteed at values ≥ 10 µF and an ESR ≤ 10 Ω within the
operating temperature range. For small tolerances of the reset delay the spread of the
capacitance of the delay capacitor and its temperature coefficient should be noted.
Semiconductor Group
5
1998-11-01