www.austriamicrosystems.com/LDOs/AS1371 Revision 1.6 9 - 17
AS1371
Datasheet - Detailed Description
8.2 Power-OK and Low-Battery-Detect Functionality
The AS1371’s power-ok or low-battery-detect circuitry is built around an N-channel MOSFET. The circuitry monitors the voltage on pin SENSE
and if the voltage goes out of regulation (e.g. during dropout, current limit or thermal shutdown) the pin POK goes low. The pin SENSE can be
connected to a resistive-divider to monitor a particular definable voltage and compare it with an internal voltage reference. If the SENSE pin is
connected to GND an internal resistive-divider is activated and connected to the output. Therefore, the Power-OK functionality can be realized
with no additional external components.
The Power-OK feature is not active during shutdown and provides a power-on-reset function that can operate down to VIN = 1.2V. A capacitor to
GND may be added to generate a power-on-reset delay. To obtain a logic-level output, connect a pull-up resistor from pin POK to pin OUT.
Larger values for this resistor will help to minimize current consumption; a 100k
resistor is perfect for most applications (see Figure 1 on page
1).
For the circuit shown in the left of Figure 14 on page 9, the input bias current into SENSE is very low, permitting large-value resistor-divider
networks while maintaining accuracy. Place the resistor-divider network as close to the device as possible. Use a defined resistor for R2 and then
calculate R
1 as:
(EQ 1)
Where:
VSENSE = 800mV ± 150mV.
In case of the SENSE pin is connected to GND, an internal resistor-divider network is activated and compares the output voltage with a 94%
(typ.) voltage threshold. For this particular Power-OK application, no external resistive components are necessary.
Figure 14. Application Diagrams
8.3 Current Limiting
The AS1371 include current limiting circuitry to protect against short-circuit conditions. The circuitry monitors and controls the gate voltage of the
P-channel MOSFET, limiting the output current to 400mA. The P-channel MOSFET output can be shorted to ground for an indefinite period of
time without damaging the device.
8.4 Thermal-Overload Protection
The devices are protected against thermal runaway conditions by the integrated thermal sensor circuitry. Thermal shutdown is an effective
instrument to prevent die overheating since the power transistor is the principle heat source in the device.
If the junction temperature exceeds 150ºC with 15ºC hysteresis, the thermal sensor starts the shutdown logic, at which point the P-channel
MOSFET is switched off. After the device temperature has dropped by approximately 15ºC, the thermal sensor will turn the P-channel MOSFET
on again. Note that this will be exhibited as a pulsed output under continuous thermal-overload conditions.
R
1
R
2
V
IN
V
SENSE
------------------
1–
=
Input
1.2V to 3.6V
C
IN
1µF
ON /
OFF
C
OUT
1µF
Output
0.6V to 3.3V
IN
EN
GND
SENSE
OUT
AS1371
POK
R
2
R
1
Input
1.2V to 3.6V
C
IN
1µF
ON /
OFF
C
OUT
1µF
Output
0.6V to 3.3V
IN
EN
GND
SENSE
OUT
AS1371
POK
External Voltage Level Detection
(Input Monitoring)
Internal Voltage Level Detection
(Output Monitoring)
R
PU
100k
R
PU
100k
