TLE4261 Datasheet, PDF (2/18 Pages) Siemens Semiconductor Group – 5-V Low-Drop Voltage Regulator

TLE 4261
Application Description
The IC regulates an input voltage V_I in the range V_I = 6 V to 40 V to V_Qrated = 5.0 V. A
reset signal is generated for a maximum output voltage of V_Q less than 4.75 V. The reset
delay can be set externally with a capacitor. A connected microprocessor is monitored
by the integrated watchdog circuit. Connecting this input to the input voltage makes the
watchdog function inactive. The presence of a voltage less than 2 V on inhibit input
disables the regulator. The current consumption drops to max. 50 µA.
Design Notes for External Components
The input capacitor C_I causes a low-resistant powerline and limits the rise times of the
input voltage. The IC is protected against rise times up to 100 V/µs. It is possible to damp
the tuned circuit consisting of supply inductance and input capacitance with a resistor of
approx. 1 Ω in series to C_I.
The output capacitor maintains the stability of the regulating loop. Stability is guaranteed
with a rating of 22 µF at an ESR of 3 Ω max. in the operating temperature range.
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 controls
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. If the output voltage
drops below 95.5 % of its typical value for more than 2 µs, a reset signal is triggered on
pin 3 and an external capacitor is discharged on pin 5. The reset signal is not cancelled
until the voltage on the capacitor has exceeded the upper switching threshold V_DT. A
positive-edge-triggered watchdog circuit monitors the connected microprocessor and
will likewise trigger a reset if pulses are missing. The IC can be disabled by a low level
on the inhibit input and the current consumption drops to < 50 µA.
The IC also incorporates a number of circuits for protection against:
q Overload
q Overvoltage
q Overtemperature
q Reverse polarity
Semiconductor Group
2
1998-11-01