LM1815 Adaptive Variable Reluctance Sensor Amplifier
February 1995
LM1815 Adaptive Variable Reluctance Sensor Amplifier
General Description
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
Features
Y
Y
Y
Y
Y
Y
Y
Adaptive hysteresis
Single supply operation
Ground referenced input
True zero crossing timing reference
Operates from 2V to 12V supply voltage
Handles inputs from 100 mV to over 120V with external
resistor
CMOS compatible logic
Applications
Y
Y
Y
Y
Y
Position sensing with notched wheels
Zero crossing switch
Motor speed control
Tachometer
Engine testing
Connection Diagram
Truth Table
Signal
Input
Pulses
X
Input
Select
L
H
Timing
Input
X
Pulses
Gated
Output
Pulses
Pulses
TL H 7893 鈥?1
Top View
Order Number LM1815M or LM1815N
See NS Package Number M14A or N14A
C
1995 National Semiconductor Corporation
TL H 7893
RRD-B30M115 Printed in U S A
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