TLE4270 Datasheet, PDF (3/19 Pages) Siemens Semiconductor Group – 5-V Low-Drop Fixed Voltage Regulator

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