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OM183SC

7.5A, 5A, 3A, 1.5A LOW DROPOUT POSITIVE ADJUSTABLE REGULATORS

Omnirel Corp => IRF 

OM183SC - OM186ST - OM186SR

APPLICATION NOTES

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

Input

Output

Adjustment

10µF 10µF Tantalum, 50µF Aluminum

None

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 IADJ is very small and constant when

compared with the current through R1, it represents a

small error and can usually be ignored.

VIN

IN OM183SC OUT

ADJ

VREF

IADJ

50 µA

( ) VOUT

=

VREF

1+

R2

R1

+ IADJ R2

VOUT

R1

R2

10µF 22µF Tantalum, 150µF Aluminum

20µF

Basic Adjustable Regulator

MECHANICAL SPECIFICATIONS

P/N OM183SC and OM184SC JEDEC TO-258AA

.695

.165

.685

.155

.270

.240

.045

.035

.707

.697

.750

.500

.200 TYP.

.835

.815

.550

.530

.065

.055

.140 TYP.

.092 MAX.

.005

12 3

Pin 1 - Adjust

Pin 2 - VOUT

Pin 3 - VIN

P/N OM185ST and OM186ST JEDEC TO-257AA

3.3

.200

.420

.190

.410

.045

.035

.665

.150

.645

.140

.537

.527

.430

.410

.038 MAX.

.750

.500

.005

.035

.100 TYP.

.025

.120 TYP.

1 23

Pin 1 - Adjust

Pin 2 - VOUT

Pin 3 - VIN

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

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