S-81211SG View Datasheet(PDF) - Seiko Instruments Inc

Part Name

Description

Manufacturer

S-81211SG

HIGH-PRECISION VOLTAGE REGULATOR

Seiko Instruments Inc 

HIGH-PRECISION VOLTAGE REGULATOR

S-812XXSG Series

Operation

1 Basic operation

Figure 4 shows the block diagram of the S-812XXSG Series.

The error amplifier compares a reference voltage VREF with a

part of the output voltage fed back by the feedback resistors

RA and RB. It supplies the control transistor with the gate

current, necessary to keep a stable output voltage range not

influenced by input voltage or temperature fluctuation.

VIN

Current

source

Reference

voltage

circuit

-

*

+

Error amplifier

RA

VOUT

RB

2 Internal circuit

2.1 Reference voltage circuit

In a voltage regulator, the reference voltage circuit plays

a very important role because any change will show up

directly at an output.

The S-812XXSG Series has 0.8 V typical stable voltage

circuit as a highly stable reference voltage source.

Features:

 Low power consumption

 Good temperature characteristic

2.2 Error amplifier

The error amplifier consumes very low current because it

is a differential amplifier in a stable current circuit.

Features:

 Good matching characteristics

 Wide operating voltage range

 Low offset voltage

2.3 Control transistor

The S-812XXSG Series has a Pch MOS transistor as a

current control transistor shown in Figure 6. Therefore

an output current IOUT is expressed by the following

formula where is only a small difference between input

and output voltages:

IOUT=KP{2(VGS-VTP) (VIN-VOUT)-(VIN-VOUT)2 }

* KP : Conductive coefficiency

VTP : Threshold voltage of a control transistor

Setting KP to the large value results in a voltage

regulator with 160 mV typical I/O voltage difference.

NOTE: A parasitic diode is generated between VIN and VOUT.

If the electric potential of VIN is higher than that of

VOUT, IC may break because of a reverse current.

Keep VOUT less than VIN+0.3 V.

GND

* Parasitic diode

Figure 4 Reference block diagram

VIN

VIN+

VOUT

VIN-

Bias

GND

Figure 5 Error amplifier

VIN

VREF

VGS

-

+

*

VOUT

GND

* Parasitic diode

Figure 6 Control transistor

Seiko Instruments Inc.

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