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
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