S-817B13AMC-CWC-T2 datasheet(14/50 Pages) SII

14 / 50 page

SUPER-SMALL PACKAGE CMOS VOLTAGE REGULATOR

S-817 Series

Rev.3.0_00

Seiko Instruments Inc.

Operation

1. Basic Operation

Figure 13 shows the block diagram of the S-817 Series.

The error amplifier compares the reference voltage (Vref) with Vfb, which is the output voltage resistance-

divided by feedback resistors Rs and Rf. It supplies the output transistor with the gate voltage necessary

to ensure a certain output voltage free of any fluctuations of input voltage and temperature.

Reference voltage

circuit

VOUT

VSS

VIN

Error

amplifier

Current

supply

Vref

−

Vfb

*1. Parasitic diode

Figure 13

2. Output Transistor

The S-817 series uses a P-channel MOS FET as the output transistor.

Be sure that VOUT does not exceed VIN

+0.3 V to prevent the voltage regulator from being damaged due to

inverse current flowing from VOUT pin through a parastic diode to VIN pin.

3. Short Circuit Protection

The S-817A series incorporates a short circuit protection to protect the output transistor against short

circuit between VOUT pin and VSS pin. Installation of the short-circuit protection which protects the

output transistor against short-circuit between VOUT and VSS can be selected in the S-817A series. The

short-circuit protection controls output current as shown in the “Typical Characteristics 1.”. Output

Voltage versus Output Current, and suppresses output current at about 40 mA even if VOUT and VSS

pins are short-circuited.

The short-circuit protection can not be a thermal protection at the same time. Attention should be paid to

the Input voltage and the load current under the actual condition so as not to exceed the power

dissipation of the package including the case for short-circuit.

When the output current is large and the difference between input and output voltage is large even if not

shorted, the short-circuit protection may work and the output current is suppressed to the specified value.

In addition, S-817B series is removing a short-circuit protection, and is the product which enabled it to

pass large current.

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