LM1815 LM1815 Adaptive Variable Reluctance Sensor Amplifier Literature Number: SNOSBU8E 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. Adaptive hysteresis Single supply operation Ground referenced input True zero crossing timing reference Operates from 2V to 12V supply voltage Handles inputs from 100 mVP-P to over 120VP-P with external resistor n CMOS compatible logic 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 150mVP-P. n n n n n n Applications n n n n n Position sensing with notched wheels Zero crossing switch Motor speed control Tachometer Engine testing Connection Diagram 00789301 Top View Order Number LM1815M or LM1815N See NS Package Number M14A or N14A (c) 2005 National Semiconductor Corporation DS007893 www.national.com LM1815 Adaptive Variable Reluctance Sensor Amplifier March 2005 LM1815 Absolute Maximum Ratings (Note 1) Storage Temperature Range If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Junction Temperature Supply Voltage Operating Temperature Range +150C 30 mA Input Current Lead Temperature (Soldering, 10 sec.) 12V Power Dissipation (Note 2) -65C TJ +150C 260C 1250 mW -40C TA +125C Electrical Characteristics Parameter (TA = 25C, VCC = 10V, unless otherwise specified, see Figure 1) Conditions Operating Supply Voltage Supply Current Pin 3 = -0.1V, Pin 9 = 2V, Pin 11 = 0.8V Reference Pulse Width fIN = 1Hz to 2kHz, R = 150k, C = 0.001F Logic Input Bias Current VIN = 2V, (Pin 9 and Pin 11) Min Typ Max Units 2.5 10 12 V 3.6 6 mA 70 100 130 s 5 A Signal Input Bias Current VIN = 0V dc, (Pin 3) Logic Threshold (Pin 9 and Pin 11) 0.8 1.1 VOUT High RL = 1k, (Pin 10) 7.5 8.6 VOUT Low ISINK = 0.1mA, (Pin 10) 0.3 -200 nA 2.0 V 0.4 V A V Output Leakage Pin 12 V12 = 11V 0.01 10 Saturation Voltage P12 I12 = 2mA 0.2 0.4 V Input Zero Crossing Threshold All Modes, VSIGNAL = 1V pk-pk 0 25 mV (Note 4) Minimum Input Arming Threshold Adaptive Input Arming Threshold -25 Mode 1, Pin 5 = Open 30 45 60 mV (Note 4) Mode 2, Pin 5 = VCC 200 300 450 mV (Note 4) Mode 3, Pin 5 = Gnd -25 0 25 mV (Note 4) Mode 1, Pin 5 = Open VSIGNAL 230mV pk-pk (Note 3) 40 80 90 % (Note 4) Mode 2, Pin 5 = VCC VSIGNAL 1.0V pk-pk (Note 3) 80 % (Note 4) Mode 3, Pin 5 = Gnd VSIGNAL 150mV pk-pk (Note 3) 80 % (Note 4) Note 1: "Absolute Maximum Ratings" are those values beyond which the safety of the device cannot be guaranteed. They are not meant to imply that the devices should be operated at these limits. The table of "Electrical Characteristics" specifies conditions of device operation. Note 2: For operation at elevated temperatures, the device must be derated based on a 150C maximum junction temperature and a thermal resistance of 80C/W (DIP), 120C/W (SO-14) junction to ambient. Note 3: Tested per Figure 1, VSIGNAL is a Sine Wave; FSIGNAL is 1000Hz. Note 4: The Min/Typ Max limits are relative to the positive voltage peak seen at VIN Pin 3. www.national.com 2 LM1815 Typical Performance Characteristics Mode 1 Minimum Arming Threshold vs Temperature Mode 2 Minimum Arming Threshold vs Temperature 00789305 00789306 Mode 3 Minimum Arming Threshold vs Temperature Mode 1 Minimum Arming Threshold vs VCC 00789307 00789308 Mode 2 Minimum Arming Threshold vs VCC Pin 3 VIN vs VSIGNAL 00789309 00789310 3 www.national.com LM1815 Typical Performance Characteristics (Continued) Pin 3 VIN vs VSIGNAL, RIN = 10k Pin 3 VIN vs VSIGNAL, RIN = 20k 00789311 00789312 Pin 3 Bias Current vs Temperature Pin 3 VIN vs VSIGNAL, RIN = 50k 00789313 00789314 Peak Detector Charge Current vs Temperature Peak Detector Charge Current vs VCC 00789315 www.national.com 00789316 4 LM1815 Typical Performance Characteristics (Continued) Peak Detector Voltage vs Pin 3 VIN, Mode 1 Peak Detector Voltage vs Pin 3 VIN, Mode 2 00789317 00789318 Peak Detector Voltage vs Pin 3 VIN, Mode 3 00789319 5 www.national.com LM1815 Truth Table Signal Input Pin 3 RC Timing Pin 14 Pulses RC X X X X H L L Pulses L L L Zero Crossing Input Select Pin 11 Timing Input Pin 9 Gated Output Pin 10 L X Pulses = RC H H H 00789302 FIGURE 1. LM1815 Adaptive Sense Amplifier www.national.com 6 Schematic Diagram 00789304 LM1815 7 www.national.com LM1815 Application Hints 00789303 FIGURE 2. LM1815 Oscillograms detectors, the LM1815 cannot be triggered until the input signal has crossed an "arming" threshold on the positivegoing 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: INPUT VOLTAGE CLAMP The signal input voltage at pin 3 is internally clamped. Current limit for the Input pin 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 1k resistor and series diode (see R4 and Q12 in the internal schematic diagram), while an active clamp limits pin 3 to typically 350mV below Ground for negative inputs (see R2, R3, Q10, and Q11 in the internal schematic diagram). Thus for input signal transitions that are more than 350mV below Ground, the input pin current (up to 3mA) will be pulled from the V+ supply. If the V+ pin is not adequately bypassed the resulting voltage ripple at the V+ pin will disrupt normal device operation. Likewise, for input signal transitions that are more than 500mV above Ground, the input pin current will be dumped to Ground through device pin 2. Slight shifts in the Ground potential at device pin 2, due to poor grounding techniques relative to the input signal ground, can cause unreliable operation. As always, adequate device grounding, and V+ bypassing, needs to be considered across the entire input voltage and frequency range for the intended application. MODE 1, PIN 5 OPEN The adaptive mode is selected by leaving device pin 5 open circuit. For input signals of less than 135mV (i.e. 270 mVp-p) and greater than typically 75mV (i.e. 150mVp-p), the input arming threshold is typically at 45mV. Under these conditions the input signal must first cross the 45mV 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 30mV peak (minimum rating in Electrical Characteristics), the one shot is guaranteed to not trigger. Input signals of greater than 230mV (i.e. 460 mVp-p) will cause the arming threshold to track at 80% of the peak input voltage. A peak detector capacitor at device 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 rapidly as the input signal amplitude increases, and decays by virtue of the resistor connected externally at pin 7 track decreases in the input signal. If the input signal amplitude falls faster than the voltage stored on the peak detector capacitor there may be a loss of output signal until the capacitor voltage has decayed to an appropriate level. Note that since the input voltage 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. INPUT CURRENT LIMITING As stated earlier, current limiting for the Input pin is provided by a user supplied external resistor. For purposes of selecting the appropriate resistor value the Input pin should be considered to be a zero ohm connection to ground. For applications where the input voltage signal is not symmetrical with relationship to Ground the worst case voltage peak should be used. Minimum Rext = [(Vin peak)/3mA] In the application example shown in figure 1 (Rext = 18k) the recommended maximum input signal voltage is 54V (i.e. 108Vp-p). OPERATION OF ZERO CROSSING DETECTOR The LM1815 is designed to operate as a zero crossing detector, triggering an internal one shot on the negativegoing edge of the input signal. Unlike other zero crossing www.national.com 8 For a given One Shot pulse width, the recommended maximum input signal frequency is: (Continued) MODE 2, PIN 5 CONNECTED TO V+ The input arming threshold is fixed at 200mV minimum when device pin 5 is connected to the positive supply. The chip has no output for signals of less than 200 mV (i.e. 400mVp-p) and triggers on the next negative-going zero crossing when the arming threshold is has been exceeded. Fin(max) = 1/(1.346 x R x C) In the application example shown in figure 1 (R=150kohms, C=0.001F) the recommended maximum input frequency will typically be 5kHz. Operating with input frequencies above the recommended Fin (max) value may result in unreliable performance of the One Shot circuitry. For those applications where the One Shot circuit is not required, device pin 14 can be tied directly to Ground. MODE 3, PIN 5 GROUNDED With pin 5 grounded, the input arming threshold is set to 0V, 25mV maximum. Positive-going zero crossings arm the chip, and the next negative-going zero crossing triggers it. This is the very basic form of zero-crossing detection. LOGIC INPUTS 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. ONE SHOT TIMING The one shot timing is set by a resistor and capacitor connected to pin 14. The recommended maximum resistor value is 150kohms. The capacitor value can be changed as needed, as long as the capacitor type does not present any signfigant leakage that would adversely affect the RC time constant. 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. The output pulse width is: pulse width = 0.673 x R x C (2) Pins 1, 4, 6 and 13 have no internal connections and can be grounded. (1) 9 www.national.com LM1815 Application Hints LM1815 Physical Dimensions inches (millimeters) unless otherwise noted 14-Lead Small Outline Circuit (M) Order Number LM1815M NS Package Number M14A www.national.com 10 LM1815 Adaptive Variable Reluctance Sensor Amplifier Physical Dimensions inches (millimeters) unless otherwise noted (Continued) Molded Dual-In-Line Package (N) Order Number LM1815N NS Package Number N14A National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. 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 AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. 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