hysteresis means that very slow moving or noisy

signals can be accommodated by the ELM409

without needing the signal to be preconditioned by

any external circuitry. (A standard CMOS input

should never have a slowly varying signal applied,

as it may cause excessive currents to flow internally,

but a Schmitt input circuit does not have this

limitation.)

Out (pin 7) and Out (pin 6)

The ‘debounced’ and processed signal is output on

pin 7, while the complement of this signal is output

on pin 6. These are high current CMOS drivers, so

will interface to virtually all of the common digital

logic families.

Circuit common is connected to this pin. This should

be the most negative point in the circuit.

ELM409

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Pin Descriptions

These integrated circuits are available in either the 300 mil plastic DIP format, or in the 208 mil SOIC surface

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

300 mil Plastic DIP............................... ELM409P

208 mil SOIC..................................... ELM409SM

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All rights reserved. Copyright 2009 by Elm Electronics Inc.

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 not required. Refer to the Electrical

Characteristics section for further information.

A, B, and C (pins 2, 3, and 4)

These three pins modify the behaviour of the

ELM409, providing eight different configurations.

They determine whether the output should follow the

input, be a momentary pulse, or toggle the output on

each input transition. As well, they can select either

a standard 25 msec debounce period, or a longer

500 msec one. The longer period may be useful for

some very noisy interfaces, or for situations that

need a slight delay. See the “ELM409 Operation”

section for more details on these options.

In (pin 5)

The signal that is to be processed is applied to this

pin. Before the signal is ‘debounced’, it is passed

through a Schmitt trigger - a special buffer circuit that

has hysteresis in its gain function. The use of

ELM409DSA

Ordering Information