S816 datasheet(9/24 Pages) SII

9 / 24 page

EXTERNAL TRANSISTOR TYPE CMOS VOLTAGE REGULATOR

Rev.6.1_00

S-816 Series

Seiko Instruments Inc.

2.2. Overcurrent Protection Circuit

The overcurrent protection function of the S-816 Series monitors the EXT pin sink current (base current of

the external PNP transistor) with an overcurrent protection circuit incorporated in the IC, and limits that

current (EXT pin sink current).

As the load current increases, the EXT pin sink current (base current of the external PNP transistor) also

grows larger to maintain the output voltage. The overcurrent protection circuit clamps and limits the EXT

pin sink current to the EXT output sink overcurrent set value (IMAX) in order to prevent it from increasing

beyond that value.

The load current at which the overcurrent protection function works is represented by the following

equation:

IOUT_MAX

= IMAX × hFE

In this case, hFE is the DC amplification factor of the external PNP transistor.

IOUT_MAX represents the maximum output current of this regulator. If it is attempted to obtain a higher load

current, the output voltage will fall.

Note that within the overcurrent protection function of this IC, the external PNP transistor may not be able

to be protected from collector overcurrents produced by an EXT-GND short-circuiting or other

phenomenon occurring outside the IC. To protect the external PNP transistor from such collector

overcurrents, it will be necessary to choose a transistor with a larger power dissipation than IOUT_MAX

× VIN,

or to add an external overcurrent protection circuit. With regard to this external overcurrent protection

circuit, refer to "1. Overcurrent Protection Circuit" in " Application Circuits".

2.3. Phase Compensation Circuit

The S-816 Series performs phase compensation with a phase compensation circuit, incorporated in the

IC, and the ESR (Equivalent Series Resistance) of an output capacitor, to secure stable operation even in

the presence of output load variation. A uniquely devised phase compensation circuit has resulted in

improved transient response characteristics of the IC, while preserving the same feature of low current

consumption. This feature allows the IC to be used in applications where the input variation or load

variation is heavy.

Because the S-816 Series is designed to perform the phase compensation, utilizing the ESR of an output

capacitor, such output capacitor (CL) should always be placed between VOUT and VSS. Since each

capacitor to be employed has an optimum range of their own characteristics, be sure to choose

components for the IC with your all attention. For details, refer to " Selection of Associated External

Components".

S816 Datasheet(PDF) 9 Page - Seiko Instruments Inc