LM1815 Adaptive Variable Reluctance Sensor Amplifier General Description Features 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. Y Connection Diagram Truth Table 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 Signal Input Input Select Timing Input Gated Output Pulses L X Pulses X H Pulses Pulses TL/H/7893 – 1 Top View Order Number LM1815M or LM1815N See NS Package Number M14A or N14A C1995 National Semiconductor Corporation TL/H/7893 RRD-B30M115/Printed in U. S. A. LM1815 Adaptive Variable Reluctance Sensor Amplifier February 1995 Absolute Maximum Ratings Storage Temperature Range If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. Supply Voltage Power Dissipation (Note 1) Operating Temperature Range 12V 1250 mW b 65§ C to a 150§ C Junction Temperature (Note 2) a 125§ C Input Current Lead Temperature (Soldering, 10 sec.) g 30 mA 260§ C b 40§ C to a 125§ C Electrical Characteristics (TA e 25§ C, VCC e 10V, unless otherwise specified, see Figure 1 ) Parameter Conditions Operating Supply Voltage Supply Current fIN e 500 Hz, Pin 9 e 2V, Pin 11 e 0.8V Reference Pulse Width fIN e 1 Hz to 2 kHz Input Bias Current VIN e 2V, (Pin 9 and Pin 11) Input Bias Current VIN e 0V dc, (Pin 3) Input Impedance VIN e 5 Vrms, (Note 3) Zero Crossing Threshold VIN e 100 mVp-p, (Pin 3) Min Typ Max Units 2.5 10 12 V 3.6 6 mA 100 130 ms 5 mA 28 kX 25 mV 70 200 12 20 Logic Threshold (Pin 9 and Pin 11) 0.8 1.1 VOUT High RL e 1 kX, (Pin 10) 7.5 8.6 VOUT Low ISINK e 0.1 mA, (Pin 10) Input Arming Threshold Pin 5 Open, VIN s 135 mVp-p nA 2.0 V V 0.3 0.4 V 30 45 60 mV Pin 5 Open, VIN t 230 mVp-p 40 80 90 % of V3 Pk Pin 5 to V a 200 Pin 5 to Gnd b 25 mV 25 mV Output Leakage Pin 12 V12 e 11V 0.01 10 mA Saturation Voltage P12 I12 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 kX 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 Schematic Diagram TL/H/7893 – 4 3 TL/H/7893 – 3 FIGURE 2. LM1815 Oscillograms Application Hints idly as the input signal amplitude increases, and decays by virtue of the resistor connected externally at pin 7 to track decreases in the input signal. Note that since the input is clamped, the waveform observed at pin 3 is not identical to the waveform observed at the variable reluctance sensor. Similarly, the voltage stored at pin 7 is not identical to the peak voltage appearing at pin 3. MODE 2, Pin 5 connected to V a . The input arming threshold is fixed at 200 mV minimum when pin 5 is connected to the positive supply. The chip has no output for signals of less than 200 mV peak, and triggers on the next negativegoing zero crossing when the threshold is exceeded. MODE 3, Pin 5 grounded. With pin 5 grounded, the input arming threshold is set to 0V ( g 25 mV maximum). Positivegoing zero crossings arm the chip, and the next negative zero crossing triggers it. The one shot timing is set by a resistor and capacitor connected to pin 14. The output pulse width is pulse width e 0.673 RC (1) Input Clamp The signal input at pin 3 is internally clamped. Current limit is provided by an external resistor which should be selected to allow a peak current of 3 mA in normal operation. Positive inputs are clamped by a 1 kX resistor and series diode, while an active clamp limits pin 3 to b350 mV for negative inputs (see R4, Q12, Q11 in internal schematic diagram). Operation of Zero Crossing Detector The LM1815 is designed to operate as a zero crossing detector, triggering an internal one shot on the negative-going edge of the input signal. Unlike other zero crossing detectors, the LM1815 cannot be triggered until the input signal has crossed an ‘‘arming’’ threshold on the positive-going portion of the waveform. The arming circuit is reset when the chip is triggered, and subsequent zero crossings are ignored until the arming threshold is exceeded again. This threshold varies depending on the connection at pin 5. Three different modes of operation are possible: MODE 1, Pin 5 open. The adaptive mode is selected by leaving pin 5 open circuit. For input signals of less than 135 mVp-p, the input arming threshold is typically 45 mV. Under these conditions the input signal must first cross the 45 mV threshold in the positive direction to arm the zero crossing detector, and then cross zero in the negative direction to trigger it. If the signal is less than 30 mV peak (minimum rating in Electrical Characteristics), the one shot is guaranteed to not trigger. Input signals of greater than 230 mVp-p cause the arming threshold to track at 80% of the peak input voltage. A peak detector (pin 7) stores a value relative to the positive input peaks to establish the arming threshold. Input signals must exceed this threshold in the positive direction to arm the zero crossing detector, which can then be triggered by a negative-going zero crossing. The peak detector tracks rap- In some systems it is necessary to externally generate pulses, such as during stall conditions when the variable reluctance sensor has no output. External pulse inputs at pin 9 are gated through to pin 10 when Input Select (pin 11) is pulled high. Pin 12 is a direct output for the one shot and is unaffected by the status of pin 11. Input/output pins 9, 11, 10 and 12 are all CMOS logic compatible. In addition, pins 9, 11 and 12 are TTL compatible. Pin 10 is not guaranteed to drive a TTL load. Pins 1, 4, 6 and 13 have no internal connections and can be grounded. 4 Physical Dimensions inches (millimeters) 14-Lead Small Outline Integrated Circuit (M) Order Number LM1815M NS Package Number M14A 5 LM1815 Adaptive Variable Reluctance Sensor Amplifier Physical Dimensions inches (millimeters) (Continued) Molded Dual-In-Line Package (N) Order Number LM1815N NS Package Number N14A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. 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