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AS1369

Datasheet - Application In form atio n

8 Application Information

Figure 46. Typical Application Diagram

Figure 46 shows the block diagram of the AS1369. It identifies the basics of a series linear regulator employing a P-Channel MOSFET as the

control element. A stable voltage reference (REF in Figure 46) 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.

8.1 Dropout Voltage

Dropout is the input to output voltage difference, below which the linear regulator ceases to regulate. At this point, the output voltage change

follows the input voltage change. Dropout voltage may be measured at different load currents, but is usually specified at maximum output. As a

result, the MOSFET maximum series resistance over temperature is obtained. More generally:

(EQ 2)

Dropout is probably the most important specification when the regulator is used in a battery application. The dropout performance of the

regulator defines the useful “end of life” of the battery before replacement or re-charge is required.

On/Off

Control

Thermal &

Over Current

Protection

_

+

GND

C2

EN

C1