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AS1358 / AS1359

Datasheet - Detailed Descr i pti on

8 Detailed Description

The AS1358 / AS1359 are ultra-low-noise, low-dropout, low-quiescent current linear-regulators specifically designed for space-limited

applications. The devices are available with preset output voltages from 1.5V to 4.5V in 50mV increments.

These devices can supply loads up to 150mA / 300mA. As shown in Figure 18, the AS1358 / AS1359 consist of an integrated bandgap core and

noise bypass circuitry, error amplifier, P-channel MOSFET pass transistor, and internal feedback voltage-divider.

Figure 18 shows the block diagram of the AS1358 / AS1359. It identifies the basics of a series linear regulator employing a 0.5

 (typ) P-Channel

MOSFET as the control element. A stable voltage reference (REF in Figure 18) is compared with an attenuated sample of the output voltage.

Any difference between the two voltages (reference and sample) creates an output from the error amplifier that drives the series control element

to reduce the difference to a minimum. The error amplifier incorporates additional buffering to drive the relatively large gate capacitance of the

series pass P-channel MOSFET, when additional drive current is required under transient conditions. Input supply variations are absorbed by the

series element and output voltage variations with loading are absorbed by the low output impedance of the regulator.

The AS1358 / AS1359 deliver preset output voltages from 1.5V to 4.5V, in 50mV increments (see Ordering Information on page 15).

The output voltage is fed back through an internal resistor voltage-divider connected to pin OUT. An external bypass capacitor connected to pin

include a current limiter, thermal sensor, and shutdown logic.

Figure 18. AS1358 / AS1359 Block Diagram

OUT

IN

SHDNN

BYPASS

GND

AS1358 /

AS1359

Thermal

Sensor

1.25 Reference and

Noise Bypass

Error

Amp

MOS

Driver w/

Shutdown and

Power-Down

Control