NSC LM1815M, LM1815N Datasheet
TL/H/7893
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 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 100 mVp-p.
Features
Y
Adaptive hysteresis
Y
Single supply operation
Y
Ground referenced input
Y
True zero crossing timing reference
Y
Operates from 2V to 12V supply voltage
Y
Handles inputs from 100 mV to over 120V with external
resistor
Y
CMOS compatible logic
Applications
Y
Position sensing with notched wheels
Y
Zero crossing switch
Y
Motor speed control
Y
Tachometer
Y
Engine testing
Connection Diagram
TL/H/7893– 1
Top View
Order Number LM1815M or LM1815N
See NS Package Number M14A or N14A
Truth Table
Signal Input Timing Gated
Input Select Input Output
Pulses L X Pulses
X H Pulses Pulses
C
1995 National Semiconductor Corporation RRD-B30M115/Printed in U. S. A.
Absolute Maximum Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Supply Voltage 12V
Power Dissipation (Note 1) 1250 mW
Operating Temperature Range
b
40§Ctoa125§C
Storage Temperature Range
b
65§Ctoa150§C
Junction Temperature (Note 2)
a
125§C
Input Current
g
30 mA
Lead Temperature (Soldering, 10 sec.) 260
§
C
Electrical Characteristics (T
A
e
25§C, V
CC
e
10V, unless otherwise specified, see
Figure 1
)
Parameter Conditions Min Typ Max Units
Operating Supply Voltage 2.5 10 12 V
Supply Current f
IN
e
500 Hz, Pin 9e2V,
3.6 6 mA
Pin 11
e
0.8V
Reference Pulse Width f
IN
e
1 Hz to 2 kHz 70 100 130 ms
Input Bias Current V
IN
e
2V, (Pin 9 and Pin 11) 5 mA
Input Bias Current V
IN
e
0V dc, (Pin 3) 200 nA
Input Impedance V
IN
e
5 Vrms, (Note 3) 12 20 28 kX
Zero Crossing Threshold V
IN
e
100 mVp-p, (Pin 3) 25 mV
Logic Threshold (Pin 9 and Pin 11) 0.8 1.1 2.0 V
V
OUT
High R
L
e
1kX, (Pin 10) 7.5 8.6 V
V
OUT
Low I
SINK
e
0.1 mA, (Pin 10) 0.3 0.4 V
Input Arming Threshold Pin 5 Open, V
IN
s
135 mVp-p 30 45 60 mV
Pin 5 Open, V
IN
t
230 mVp-p 40 80 90 % of V3Pk
Pin5toV
a
200 mV
Pin 5 to Gnd
b
25 25 mV
Output Leakage Pin 12 V
12
e
11V 0.01 10 mA
Saturation Voltage P12 I
12
e
2 mA 0.2 0.4 V
Note 1: For operation at elevated temperatures, the device must be derated based on a 125§C maximum junction temperature and a thermal resistance of 80§C/W
(DIP), 120
§
C/W (SO-14) junction to ambient.
Note 2: Temporary excursions to 150
§
C can be tolerated.
Note 3: Measured at input to external 18 k X resistor. IC contains 1 kX in series with a diode to attenuate the input signal.
TL/H/7893– 2
FIGURE 1. LM1815 Adaptive Sense Amplifier
2
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