Datasheet

TLF80511
Block Description and Electrical Characteristics
Data Sheet 1 Rev. 1.0, 2012-06-15
5 Block Description and Electrical Characteristics
5.1 Voltage Regulation
The output voltage V
Q
is divided by a resistor network. This fractional voltage is compared to an internal voltage
reference and drives the pass transistor accordingly.
The control loop stability depends on the output capacitor
C
Q
, the load current, the chip temperature and the
internal circuit design. To ensure stable operation, the output capacitor’s capacitance and its equivalent series
resistor ESR requirements given in Table 4.2 “Functional Range” on Page 2 must be maintained. For details
see the typical performance graph “Stability Region: Equivalent Serial Resistor ESR versus Output Current
I
Q
” on Page 6. Since the output capacitor is used to buffer load steps, it should be sized according to the
application’s needs.
An input capacitor
C
I
is not required for stability, but is recommended to compensate line fluctuations. An
additional reverse polarity protection diode and a combination of several capacitors for filtering should be used.
Connect the capacitors close to the regulator terminals.
Whenever the load current exceeds the specified limit, e.g. in case of a short circuit, the output current is limited
and the output voltage decreases.
The overtemperature 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, the regulator
restarts. This oscillatory thermal behaviour causes the junction temperature to exceed the 150° C maximum and
significantly reducing the IC’s life.
Figure 3 Block Diagram Voltage Regulation
LOAD
Supply
C
I
Regulated
Output Voltage
I
Q
I
I
V
I
V
Q
C
ESR
C
Q
Bandgap
Reference
GND
Q
I
ApplicationDiagram.vsd
Current
Limitation
Temperature
Shutdown