ELM331

Elm Electronics – Circuits for the Hobbyist

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Pin Descriptions

Ordering Information

These integrated circuits are available in either the 300 mil plastic DIP format, or in the 200 mil SOIC surface

mount type of package. To order, add the appropriate suffix to the part number:

300 mil Plastic DIP............................... ELM331P

200 mil SOIC..................................... ELM331SM

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All rights reserved. Copyright ©1999 Elm Electronics.

Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be

given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information

described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these

products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or

systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve

reliability, function, or design.

This pin is the positive supply pin, and should

always be the most positive point in the circuit.

Internal circuitry connected to this pin is used to

provide power on reset of the microprocessor, so

an external reset signal is normally not required.

Refer to the Electrical Characteristics section for

further information.

One

of

the

two

resistance

input

pins.

A

temperature dependent resistance is usually

connected to this input for heating or under-

temperature alarm type applications. When the

value of this resistor is greater than the value of

the resistance connected to pin 3

(for three

successive measurements) the output will be

driven high.

The reference resistance is connected to this pin

for heating applications, and the temperature

dependent resistance is connected here for

cooling applications. The other end of this resistor

is connected to the integrating capacitor.

reset (pin 4)

The active low reset input. An internal pullup

resistor is provided for convenience. If unused,

Cap (pin 5)

Temperature

measurements

are

made

by

determining the time to charge and discharge this

integrating capacitor. Pin 5 forces the capacitor to

a known voltage for these measurements though,

resulting in large current flows. To limit these

capacitor currents, and protect the ELM331, a

series resistor must be connected to this pin. The

value of the resistance, and of the capacitance, is

not critical to the measurements.

MIP (pin 6)

This pin provides a logic high level output while

the ELM331 is busy (measurements are in

progress). It is suitable for directly driving an LED

through a current limiting resistor. As a warning,

this output pulses rapidly if either resistor input is

found to be open circuited.

Out (pin 7)

The output pin assumes a logic high state once

successive measurement cycles. The output is

hysteresis amount for an additional three counts.

Circuit common is connected to this pin. This is

the most negative point in the circuit.

ELM331DSB