1FEATURES

2• Adaptive Hysteresis

• Single Supply Operation

• Ground Referenced Input

• True Zero Crossing Timing Reference

• Operates from 2V to 12V Supply Voltage

• Handles Inputs from 100 mVP-P to over 120VP-P with External Resistor

• CMOS Compatible Logic

APPLICATIONS

• Position Sensing with Notched Wheels positive•

Zero Crossing Switch

• Motor Speed Control

• Tachometer

• Engine Testing

DESCRIPTION

The LM1815 is an adaptive sense amplifier and

default gating circuit for motor control applications.

The sense amplifier provides a one-shot pulse output

whose leading edge coincides with the negative-

going zero crossing of a ground referenced input

signal such as from a variable reluctance magnetic pick-up coil.

In normal operation, this timing reference signal is

processed (delayed) externally and returned to the

LM1815. A Logic input is then able to select either

the timing reference or the processed signal for

transmission to the output driver stage.

The adaptive sense amplifier operates with a positive•

going threshold which is derived by peak detecting

the incoming signal and dividing this down. Thus the

input hysteresis varies with input signal amplitude.

This enables the circuit to sense in situations where

the high speed noise is greater than the low speed

signal amplitude. Minimum input signal is 150mVP-P.