www.austriamicrosystems.com

Revision 1.03

8 - 13

AS1353/AS1356

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

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 0.5

Ω (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.

SHDNM

AS1353/AS1356

IN

+

–

GND

Reverse-

Battery

Protection

OUT

+

-

POK

2

Error

Amplifier

Thermal

Overload

Protection

Bandgap Voltage

&

Current Reference

95%

Shutdown/

Power-On

Control Logic

Trimmable

Reference

Voltage

BP

1

1

AS1353 only

2

AS1356 only

AS1356 only