Datasheet

TLE42694
Block Description and Electrical Characteristics
Data Sheet 11 Rev. 1.2, 2010-11-26
5 Block Description and Electrical Characteristics
5.1 Voltage Regulator
The output voltage V
Q
is controlled by comparing a portion of it to an internal reference and driving a PNP pass
transistor accordingly. The control loop stability depends on the output capacitor
C
Q
, the load current, the chip
temperature and the poles/zeros introduced by the integrated circuit. To ensure stable operation, the output
capacitor’s capacitance and its equivalent series resistor ESR requirements given in the table “Functional
Range” on Page 9 have to be maintained. For details see also the typical performance graph “Output Capacitor
Series Resistor ESR(C
Q
) versus Output Current I
Q
” on Page 14. As the output capacitor also has to buffer load
steps it should be sized according to the application’s needs.
An input capacitor
C
I
is strongly recommended to compensate line influences. Connect the capacitors close to the
component’s terminals.
A protection circuitry prevents the IC as we
ll as the application from destruction in case of catastrophic events.
These safeguards contain an output current limitation, a reverse polarity protection as well as a thermal shutdown
in case of overtemperature.
In order to avoid excessive power dissipation that could n
ever be handled by the pass element and the package,
the maximum output current is decreased at input voltages above
V
I
= 22 V.
The thermal shutdown circuit prevents the IC from immed
iate destruction under fault conditions (e.g. output
continuously short-circuited) by switching off the power stage. After the chip has cooled down, the regulator
restarts. This leads to an oscillatory behaviour of the output voltage until the fault is removed. However, junction
temperatures above 150 °C are outside the maximum ratings and therefor
e significantly reduce the IC’s lifetime.
The TLE 42694 allows a negative supply voltage. In this fault co
ndition, small currents are flowing into the IC,
increasing its junction temperature. This has to be considered for the thermal design, respecting that the thermal
protection circuit is not operating during reverse polarity conditions.
Bandgap
Refer ence
GND
QI
BlockDiagram_VoltageRegulator.vsd
Saturation Control
Curr ent Limi tation
Tem peratur e
Shutdown
C
Q
LOAD
Supply
C
I
Regulated
Output Voltage
I
Q
I
I
Figure 5 Voltage Regulator