LP395

Ultra Reliable Power Transistor

General Description

The LP395 is a fast monolithic transistor with complete over-

load protection. This very high gain transistor has included

on the chip, current limiting, power limiting, and thermal

overload protection, making it difficult to destroy from almost

any type of overload. Available in an epoxy TO-92 transistor

package this device is guaranteed to deliver 100 mA.

Thermal limiting at the chip level, a feature not available in

discrete designs, provides comprehensive protection against

overload. Excessive power dissipation or inadequate heat

sinking causes the thermal limiting circuitry to turn off the de-

vice preventing excessive die temperature.

The LP395 offers a significant increase in reliability while

simplifying protection circuitry. It is especially attractive as a

small incandescent lamp or solenoid driver because of its

low drive requirements and blowout-proof design.

The LP395 is easy to use and only a few precautions need

be observed. Excessive collector to emitter voltage can de-

stroy the LP395 as with any transistor. When the device is

used as an emitter follower with a low source impedance, it

is necessary to insert a 4.7 k

Ω resistor in series with the

base lead to prevent possible emitter follower oscillations.

Also since it has good high frequency response, supply

by-passing is recommended.

Areas where the LP395 differs from a standard NPN transis-

tor are in saturation voltage, leakage (quiescent) current and

in base current. Since the internal protection circuitry re-

quires voltage and current to function, the minimum voltage

across the device in the on condition (saturated) is typically

1.6 Volts, while in the off condition the quiescent (leakage)

current is typically 200 µA. Base current in this device flows

out of the base lead, rather than into the base as is the case

with conventional NPN transistors. Also the base can be

driven positive up to 36 Volts without damage, but will draw

current if driven negative more than 0.6 Volts. Additionally, if

the base lead is left open, the LP395 will turn on.

The LP395 is a low-power version of the 1-Amp LM195/

LM295/LM395 Ultra Reliable Power Transistor.

The LP395 is rated for operation over a −40˚C to +125˚C

range.

Features

n Internal thermal limiting

n Internal current and power limiting

n Guaranteed 100 mA output current

n 0.5 µA typical base current

n Directly interfaces with TTL or CMOS

n +36 Volts on base causes no damage

n 2 µs switching time

Connection Diagram

Typical Applications

TO-92 Package

DS005525-1

Order Number LP395Z

See NS Package Z03A

Fully Protected Lamp Driver

DS005525-3

April 1998

© 1999 National Semiconductor Corporation

DS005525

www.national.com