S-817B13AMC-CWC-T2 datasheet(15/50 Pages) SII

15 / 50 page

SUPER-SMALL PACKAGE CMOS VOLTAGE REGULATOR

Rev.3.0_00

S-817 Series

Seiko Instruments Inc.

Selection of Output Capacitor (CL)

To stabilize operation against variation in output load, a capacitor (CL) must be mounted between VOUT

and VSS in the S-817 series because the phase is compensated with the help of the internal phase

compensation circuit and the ESR of the output capacitor.

When selecting a ceramic or an OS capacitor, capacitance should be 0.1

µF or more, and when selecting a

tantalum or an aluminum electrolytic capacitor, capacitance should be 0.1

µF or more and ESR 30 Ω or

less.

When an aluminum electrolytic capacitor is used attention should be especially paid to since the ESR of the

aluminum electrolytic capacitor increases at low temperature and possibility of oscillation becomes large.

Sufficient evaluation including temperature characteristics is indispensable.

Overshoot and undershoot

characteristics differ depending upon the type of the output capacitor.

Refer to CL dependencies in “

Reference Data 1. Transient Response Characteristics”.

Application Circuits

1. Output Current Boosting Circuit

Tr1

GND

VOUT

VIN

VSS

VIN

VOUT

S-817

series

CIN

Figure 14

As shown in Figure 14, the output current can be boosted by externally attaching a PNP transistor. The

base current of the PNP transistor is controlled so that output voltage (VOUT) goes the voltage specified

in the S-817 Series when base-emitter voltage (VBE) necessary to turn on the PNP transistor is obtained

between input voltage (VIN) and S-817 Series power source pin (VIN).

The following are tips and hints for selecting and ensuring optimum use of external parts

• PNP transistor (Tr1):

1. Set hFE to approx. 100 to 400.

2. Confirm that no problem occurs due to power dissipation under normal operation conditions.

• Resistor (R1):

Generally set R1 to 1 k

Ω ÷ VOUT (S) (the voltage specified in the S-817 Series) or more.

• Output capacitor (CL):

Output capacitor (CL) is effective in minimizing output fluctuation at powering on or due to power

or load fluctuation, but oscillation might occur. Always connect resistor R2 in series to output

capacitor CL.

• Resistor (R2): Set R2 to 2 Ω × VOUT(S) or more.

• DO NOT attach a capacitor between the S-817 Series power source (VIN) and GND pins or

between base and emitter of the PNP transistor to avoid oscillation.

• To improve transient response characteristics of the output current boosting circuit shown in

Figure 14, check that no problem occurs due to output fluctuation at powering on or due to

power or load fluctuation under normal operating conditions.

• Pay attention to the short current limit circuit incorporated into the S-817 Series because it does

not function as a shortcircuiting protection circuit for this boosting circuit.

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