AND9129D datasheet(2/7 Pages) ONSEMI

2 / 7 page

December, 2013 − Rev. 1

Publication Order Number:

AND9129/D

Understanding a Digital

Transistor Datasheet

Introduction

This application note will describe the common

specifications of a Digital Transistor. It will also show how

to use these specifications to successfully design with a

Digital Transistor. Parameters from the DTC114E/D

datasheet will be used to help with explanations. This

datasheet describes a Digital Transistor that has an input

resistor, R1, equal to 10 k

W and a base−emitter resistor, R2,

equal to 10 k

W. Figure 1 gives a labeled schematic of a

Digital Transistor. These labels will be used throughout this

application note.

Figure 1. Labeled Schematic

For Digital Transistors it is important to realize that the

transistor and resistor network is considered as one unit. An

example of this is the ICBO parameter. Looking at this

parameter one would think that it is not possible. How could

the emitter be open when R2 connects the emitter and base

of the transistor? Shouldn’t it be ICER? The answer is yes R2

connects the emitter and base of the transistor, but this

connection is built into the device. What is considered the

emitter and base of the Digital Transistor is left open. In the

case of a Digital Transistor ICER would mean that there is an

additional resistor placed between the emitter and base of the

digital transistor. Figure 2 shows the difference between

ICBO and ICER when referring to Digital Transistors.

Figure 2. ICBO vs. ICER

Maximum Ratings

Below is the maximum ratings table that can be found in

every Digital Transistor datasheet.

Table 1. MAXIMUM RATINGS

Rating

Symbol

Max

Unit

Collector−Base Voltage

VCBO

Vdc

Collector−Emitter Voltage

VCEO

Vdc

Collector Current – Continuous

100

mAdc

Input Forward Voltage

VIN(fwd)

Vdc

Input Reverse Voltage

VIN(rev)

Vdc

Stresses exceeding those listed in the Maximum Ratings table

may damage the device. If any of these limits are exceeded,

device functionality should not be assumed, damage may occur

and reliability may be affected.

The first spec, VCBO, states that the maximum voltage that

can be applied from the collector to the base is 50 V. The

Collector−Emitter Voltage, VCEO, spec states the maximum

voltage that can be applied from the collector to emitter is

50 V. In addition, the table specifies that the maximum DC

collector current (IC) that the device can conduct is 100 mA.

There are two maximum ratings for the input voltage,

forward and reverse. The input voltage is defined as the

voltage applied from the base and the emitter. The maximum

input forward voltage is determined from the power

capabilities of the input resistor, R1. Figure 3 and Equations

1 and 2 describe how the maximum input forward voltage is

calculated when the maximum power capability of R1 is

220 mW. It is important to use the minimum value of R1

because it will cause the greatest power to be dissipated on the

die. The minimum value of R1 can be found in the Electrical

Characteristics Table of every Digital Transistor datasheet. In

this case R1(min) = 7 k

W. The resulting maximum input

forward voltage is 40 V. For this particular device a voltage

greater than this would result in the resistor failing.

APPLICATION NOTE

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