TLE4678 Datasheet, PDF (11/31 Pages) Infineon Technologies AG – Low Drop Out Linear Voltage Regulator 5 V Fixed Output Voltage

TLE4678
Voltage Regulator
5
Voltage Regulator
5.1
Description 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. Saturation control as a function of the load current prevents any oversaturation of the pass
element. 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_CQ vs.
Output Current I_Q”. Also, the output capacitor shall be sized to buffer load transients.
An input capacitor C_I is not needed for the control loop stability, but recommended to buffer line influences.
Connect the capacitors close to the IC terminals.
Protection circuitry prevent the IC as well as the application from destruction in case of catastrophic events. These
safeguards contain output current limitation, reverse polarity protection as well as thermal shutdown in case of
overtemperature.
In order to avoid excessive power dissipation that could never 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 immediate 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, a junction
temperature above 150 °C is outside the maximum rating and therefore reduces the IC lifetime.
The TLE4678 allows a negative supply voltage. However, several 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 condition.
Supply
I_I
I
+
Saturation Control
Current Limitation
VI
C_I
Temperature
Shutdown
BlockDiagram _VoltageRegulator .vsd
Bandgap
Reference
GND
Figure 4 Block Diagram Voltage Regulator Circuit
Regulated
Q
IQ
Output Voltage
+
CQ
VQ
LOAD
9
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9,
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Figure 5 Output Voltage vs. Input Voltage
Datasheet
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Rev. 1.1, 2009-08-27