3.3

205 Crawford Street, Leominster, MA 01453 USA (508) 534-5776 FAX (508) 537-4246

OM183SC - OM186ST - OM186SR

.707

.697

.750

.500

.835

.815

.695

.685

.165

.155

.200 TYP.

.550

.530

.270

.240

.045

.035

.140 TYP.

.092 MAX.

.065

.055

.005

Pin 1 - Adjust

12

3

Pin 1 - Adjust

12

3

MECHANICAL SPECIFICATIONS

P/N OM183SC and OM184SC JEDEC TO-258AA

.430

.410

.200

.190

.038 MAX.

.005

.120 TYP.

.537

.527

.665

.645

.420

.410

.150

.140

.750

.500

.100 TYP.

.035

.025

.045

.035

P/N OM185ST and OM186ST JEDEC TO-257AA

Stability

The OM183-186 Series requires the use of an output

capacitor as part of the device frequency compensation.

For all operating conditions, the addition of 150µF alu-

minum electrolytic or a 22µF solid tantalum on the output

will ensure stability. Normally, capacitors much smaller

than this can be used. Many different types of capacitors

with widely varying characteristics are available. These

capacitors differ in capacitor tolerance (sometimes ranging

up to ±100%), equivalent series resistance, and capaci-

tance

temperature

coefficient.

The 150µF or 22µF values given will ensure stability.

When the adjustment terminal is bypassed to improve the

ripple rejection, the requirement for an output capacitor

increases. The values of 22µF tantalum or 150µF alu-

minum cover all cases of bypassing the adjustment termi-

nal. Without bypassing the adjustment terminal, smaller

capacitors can be used with equally good results and the

table below shows approximately what size capacitors are

needed to ensure stability.

Recommended Capacitor Values

Normally, capacitor values on the order of 100µF are used

in the output of many regulators to ensure good transient

response with heavy load current changes. Output capac-

itance can be increased without limit and larger values of

output capacitor further improve stability and transient

response of the OM183SC regulators.

Output Voltage — Adjustable Regulators

The OM183-OM186 devices develop a 1.25V reference

voltage between the output and the adjust terminal (see

below). By placing a resistor, R1, between these two ter-

minals, a constant current is caused to flow through R1

and down through R2 to set the overall output voltage.

Normally this current is the specified minimum load current

of 10mA. Because I

compared with the current through R1, it represents a

small error and can usually be ignored.

Basic Adjustable Regulator

APPLICATION NOTES

Input

Output

Adjustment

10µF

10µF Tantalum, 50µF Aluminum

None

10µF

22µF Tantalum, 150µF Aluminum

20µF

V

IN

V

OUT

IN

OUT

OM183SC

ADJ

I

ADJ

50 µA

V

REF

V

R2

R1

R2

R1