S-816 Datasheet, PDF (9/24 Pages) Seiko Instruments Inc – EXTERNAL TRANSISTOR TYPE CMOS VOLTAGE REGULATOR

Rev.5.1_00
EXTERNAL TRANSISTOR TYPE CMOS VOLTAGE REGULATOR
S-816 Series
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 (I_MAX) 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:
I_{OUT_MAX} = I_MAX × h_FE
In this case, h_FE is the DC amplification factor of the external PNP transistor.
I_{OUT_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 I_{OUT_MAX} × V_IN,
or to add an external overcurrent protection circuit. With regard to this external overcurrent protection
circuit, refer to "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 (C_L) 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".
Seiko Instruments Inc.
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