AS1353/AS1356
Data Sheet - Detailed Description
8 Detailed Description
The AS1353/AS1356 are low-dropout, low-quiescent-current linear regulators intended for LDO regulator applications
where output current load requirements range from no load to 150mA. All devices come standard with fixed output volt-
ages of 1.5 to 3.6V (see Ordering Information on page 12).
Figure 12. Block Diagram
AS1353/AS1356
AS1356 only
IN
Reverse-
Battery
Protection
SHDNM
Shutdown/
Power-On
Thermal
Overload
Protection
Control Logic
-
Error
Amplifier
OUT
+
R2
R1
Trimmable
Reference
Voltage
Bandgap Voltage
&
Current Reference
2
1
POK
1
BP
–
+
95%
GND
AS1353 only
AS1356 only
2
As illustrated in Figure 12, the devices comprise a 1.25V reference, error amplifier, P-channel MOSFET pass transis-
tor, power-OK comparator, internal feedback voltage divider, current limiter, reverse-battery protection, thermal sensor
and shutdown logic.
The 1.25V bandgap reference is connected to the inverting input of the error amplifier. The error amplifier compares
this reference with the feedback voltage and amplifies the difference. If the feedback voltage is lower than the refer-
ence voltage, the P-channel MOSFET gate is pulled lower, allowing more current to pass to the output, and increases
the output voltage. If the feedback voltage is too high, the pass-transistor gate is pulled up, allowing less current to
pass to the output. The output voltage feeds back through an internal resistor voltage divider connected to pin OUT.
Output Voltages
Standard products are factory-set with output voltages of from 1.5 to 3.6V. A two-digit suffix of the part number identi-
fies the nominal output voltage (see Ordering Information on page 12).
Non-standard devices are available. Contact austriamicrosystems AG for more information.
Internal P-Channel MOSFET Pass Transistor
The integrated 0.5Ω (typ) P-channel MOSFET pass transistor requires no base drive, which reduces quiescent current
significantly, and does not exhibit the problems associated with PNP-based regulators, such as dropout when the pass
transistor saturates or high base-drive currents under large load conditions.
The devices consume only 115µA quiescent current in dropout, light-load, or heavy-load applications (see Typical
Operating Characteristics on page 6).
Power-OK
The AS1356’s power-ok circuitry is built around an N-channel MOSFET. The circuitry monitors the voltage on pin 5
(OUT) and if the voltage goes out of regulation (e.g. during dropout, current limit, or thermal shutdown) pin POK goes
low.
www.austriamicrosystems.com
Revision 1.03
8 - 13
AMSCO [ AMS(艾迈斯) ]
