TLE4678-2_15 Datasheet, PDF (9/33 Pages) Infineon Technologies AG – Low Drop Out Linear Voltage Regulator

5
Voltage Regulator
TLE4678-2
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 chapter Chapter 4.2 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 behavior 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 TLE4678-2 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
II
I
Regulated
Q
I_Q
Output Voltage
Saturation Control
Current Limitation
VI
CI
Temperature
Shutdown
Bandgap
Reference
BlockDiagram_VoltageRegulator.vsd
GND
Figure 3 Block Diagram Voltage Regulator Circuit
C
VQ
ESR
CQ
LOAD
V
VQ,nom
VI(ext),min
VI
Vdr
VQ
Diagram_Output-InputVoltage.svg
Figure 4 Output Voltage vs. Input Voltage
Data Sheet
dVQ
dt
≈
Iload
CQ
9
dVQ
dt
≈
I I Q,max - load
CQ
t
Rev. 1.0, 2014-03-03