EXTERNAL TRANSISTOR TYPE CMOS VOLTAGE REGULATOR

S-816 Series

10

Seiko Instruments Inc.

Selection of Associated External Components

1. External PNP Transistor

Select an external transistor according to the conditions of input voltage, output voltage, and output

IC.

The parameters for selection of the external PNP transistor include the maximum collector-base voltage,

and the collector dissipation.

The maximum collector-base voltage and the maximum collector-emitter voltage are determined by the

input voltage range in each specific application to be employed. You may select a transistor with an input

voltage at least several volts higher than the expected maximum input voltage.

With an internal overcurrent protection circuit of this IC, the base current is clamped, and will not exceed

output current to the intended application, with hfe and maximum collector current. (Refer to

" Overcurrent Protection Circuit")

Likewise, select a transistor, based on the maximum output current and the difference between the input

and output voltages, with due attention to the collector dissipation.

The S-816 Series performs phase compensation by an internal phase compensation circuit of IC, and the

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

µF or more between

VOUT and VSS.

For stable operation of the S-816 Series, it is essential to employ a capacitor with an ESR having

optimum range. Whether an ESR is larger or smaller than that optimum range (approximately 0.1

Ω to

5

Ω), this could produce an unstable output, and cause a possibility of oscillations. For this reason, a

tantalum electrolytic capacitor is recommended.

When a ceramic capacitor or an OS capacitor having a low ESR is selected, it will be necessary to

connect an additional resistance that serves for the ESR in series with the output capacitor, as illustrated

in Figure 9. The resistance value that needs to be added will be from 0.1

Ω to 5 Ω, but this value may

vary depends on the service conditions, and should be defined through careful evaluation in advance. In

general, our recommendation is 0.3

Ω or so.

An aluminum electrolytic capacitor tends to produce oscillations as its ESR increases at a low

temperature. Beware of this case. When this type of capacitor is employed, make thorough evaluation of

it, including its temperature characteristics.

OUT

IN

R

≅ 0.3 Ω

S-816 Series

EXT

VOUT

VSS

OFF

ON/

VIN

Figure 9

Caution The above connection diagram and constant will not guarantee successful operation.

Perform through evaluation using the actual application to set the constant.