The LM1815 is an adaptive sense amplifier and default gat-
ing circuit for motor control applications. The sense amplifi-
er 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 process-
ed (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 var-
ies 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 100 mVp-p.