Rev.1.0

HIGH OPERATING VOLTAGE CMOS VOLTAGE REGULATOR

S-812C Series

Seiko Instruments Inc.

7

5. Dropout voltage (Vdrop)

6. Temperature coefficient of output voltage [

∆V

The output voltage lies in the shaded area in the whole operating temperature shown in figure 8 when the

temperature coefficient of the output voltage is

±100 ppm/°C.

-40

25

+0.30mV/

°C

[V]

output voltage at 25

°C.

85

Ta [

°C]

-0.30mV/

°C

Figure 8 Example for the S-812C30A

Temperature change ratio for output voltage [mV/°C] is calculated by using the following equation.

[]

[ ]

[]

∆

∆

∆

∆

V

Ta

mV/ C

V

(S) V

V

Ta V

ppm/ C

1000

OUT

OUT

OUT

OUT

°=

×

•

°÷

„ Description of Operation

1. Basic operation

Figure 9 shows the block diagram of the S-812C

series.

The error amplifier compares a reference voltage

feedback resistors Rs and Rf, and supplies the gate

voltage to the output transistor, necessary to ensure

certain output voltage independent from change of

input voltage and temperature.

2. Output transistor

The S-812C Series uses a Pch MOS transistor as the output transistor.

The voltage at VOUT must not exceed VIN+0.3V. When the VOUT voltage becomes higher than that of VIN,

reverse current flows and may break the regulator since a parasitic diode between VOUT and VIN exists

inevitably.

Reference

voltage

VOUT

*

* : Parasitic diode

VSS

VIN

Rs

Rf

Figure 9 Block Diagram

Error amplifier

Current

source

Vref

Specified output voltage

Output voltage temperature coefficient

Temperatures change ratio for output voltage