LM2907,LM2917 LM2907/LM2917 Frequency to Voltage Converter Literature Number: SNAS555B LM2907/LM2917 Frequency to Voltage Converter General Description The LM2907, LM2917 series are monolithic frequency to voltage converters with a high gain op amp/comparator designed to operate a relay, lamp, or other load when the input frequency reaches or exceeds a selected rate. The tachometer uses a charge pump technique and offers frequency doubling for low ripple, full input protection in two versions (LM2907-8, LM2917-8) and its output swings to ground for a zero frequency input. The op amp/comparator is fully compatible with the tachometer and has a floating transistor as its output. This feature allows either a ground or supply referred load of up to 50 mA. The collector may be taken above VCC up to a maximum VCE of 28V. The two basic configurations offered include an 8-pin device with a ground referenced tachometer input and an internal connection between the tachometer output and the op amp non-inverting input. This version is well suited for single speed or frequency switching or fully buffered frequency to voltage conversion applications. The more versatile configurations provide differential tachometer input and uncommitted op amp inputs. With this version the tachometer input may be floated and the op amp becomes suitable for active filter conditioning of the tachometer output. Both of these configurations are available with an active shunt regulator connected across the power leads. The regulator clamps the supply such that stable frequency to voltage and frequency to current operations are possible with any supply voltage and a suitable resistor. Advantages ■ Output swings to ground for zero frequency input ■ Easy to use; VOUT = fIN × VCC × R1 × C1 ■ Only one RC network provides frequency doubling ■ Zener regulator on chip allows accurate and stable frequency to voltage or current conversion (LM2917) Features ■ Ground referenced tachometer input interfaces directly with variable reluctance magnetic pickups ■ Op amp/comparator has floating transistor output ■ 50 mA sink or source to operate relays, solenoids, meters, or LEDs ■ Frequency doubling for low ripple ■ Tachometer has built-in hysteresis with either differential input or ground referenced input ■ Built-in zener on LM2917 ■ ±0.3% linearity typical ■ Ground referenced tachometer is fully protected from damage due to swings above VCC and below ground Applications ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Over/under speed sensing Frequency to voltage conversion (tachometer) Speedometers Breaker point dwell meters Hand-held tachometer Speed governors Cruise control Automotive door lock control Clutch control Horn control Touch or sound switches Connection Diagrams Dual-In-Line and Small Outline Packages, Top Views 794201 Order Number LM2907M-8 or LM2907N-8 See NS Package Number M08A or N08E © 2008 National Semiconductor Corporation 7942 794202 Order Number LM2917M-8 or LM2917N-8 See NS Package Number M08A or N08E www.national.com LM2907/LM2917 Frequency to Voltage Converter December 9, 2008 LM2907/LM2917 794203 794204 Order Number LM2907M or LM2907N See NS Package Number M14A or N14A Order Number LM2917M or LM2917N See NS Package Number M14A or N14A Ordering Information Order Number Package Type Package Number Package Marking Supplied As LM2907M-8 8-Pin SOIC Narrow M08A LM2907M-8 Rail of 95 LM2907MX-8 8-Pin SOIC Narrow M08A LM2907M-8 Reel of 2500 LM2907M 14-Pin SOIC Narrow M14A LM2907M Rail of 55 LM2907MX 14-Pin SOIC Narrow M14A LM2907M Reel of 2500 LM2907N-8 8-Pin Molded DIP N08E LM2907N-8 Rail of 40 LM2907N 14-Pin Molded DIP N14A LM2907N Rail of 25 LM2917M-8 8-Pin SOIC Narrow M08A LM2917M-8 Rail of 95 LM2917MX-8 8-Pin SOIC Narrow M08A LM2917M-8 Reel of 2500 LM2917M 14-Pin SOIC Narrow M14A LM2917M Rail of 55 LM2917MX 14-Pin SOIC Narrow M14A LM2917M Reel of 2500 LM2917N-8 8-Pin Molded DIP N08E LM2917N-8 Rail of 40 LM2917N 14-Pin Molded DIP N14A LM2917N Rail of 25 www.national.com 2 If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage Supply Current (Zener Options) Collector Voltage Differential Input Voltage Tachometer Op Amp/Comparator Input Voltage Range Tachometer LM2907-8, LM2917-8 LM2907, LM2917 28V 25 mA 28V 28V 28V ±28V 0.0V to +28V 0.0V to +28V 1200 mW 1580 mW −40°C to +85°C −65°C to +150°C 260°C 215°C 220°C Electrical Characteristics VCC = 12 VDC, TA = 25°C, see test circuit Symbol Parameter Conditions Min Typ Max Units ±10 ±25 ±40 mV TACHOMETER Input Thresholds VIN = 250 mVp-p @ 1 kHz (Note 2) Hysteresis VIN = 250 mVp-p @ 1 kHz (Note 2) Offset Voltage VIN = 250 mVp-p @ 1 kHz (Note 2) 30 LM2907/LM2917 LM2907-8/LM2917-8 mV 3.5 5 10 15 mV mV 1 μA Input Bias Current VIN = ±50 mVDC 0.1 VOH Pin 2 VIN = +125 mVDC (Note 3) 8.3 V VOL Pin 2 VIN = −125 mVDC (Note 3) 2.3 V I2, I3 Output Current V2 = V3 = 6.0V (Note 4) I3 Leakage Current I2 = 0, V3 = 0 K Gain Constant (Note 3) 0.9 1.0 1.1 Linearity fIN = 1 kHz, 5 kHz, 10 kHz (Note 5) −1.0 0.3 +1.0 % 140 180 240 μA 0.1 μA OP/AMP COMPARATOR VOS VIN = 6.0V 3 10 mV IBIAS VIN = 6.0V 50 500 nA Input Common-Mode Voltage 0 Voltage Gain 40 VCC−1.5V V 200 V/mV 50 mA Output Sink Current VC = 1.0 Output Source Current VE = VCC −2.0 10 Saturation Voltage ISINK = 5 mA 0.1 ISINK = 20 mA ISINK = 50 mA 1.0 RDROP = 470Ω 7.56 mA 0.5 V 1.0 V 1.5 V ZENER REGULATOR Regulator Voltage Series Resistance 10.5 Temperature Stability +1 Total Supply Current 3.8 V 15 Ω mV/°C 6 mA Note 1: For operation in ambient temperatures above 25°C, the device must be derated based on a 150°C maximum junction temperature and a thermal resistance of 101°C/W junction to ambient for LM2907-8 and LM2917-8, and 79°C/W junction to ambient for LM2907-14 and LM2917-14. Note 2: Hysteresis is the sum +VTH − (−VTH), offset voltage is their difference. See test circuit. Note 3: VOH is equal to ¾ × VCC − 1 VBE, VOL is equal to ¼ × VCC − 1 VBE therefore VOH − VOL = VCC/2. The difference, VOH − VOL, and the mirror gain, I2/I3, are the two factors that cause the tachometer gain constant to vary from 1.0. Note 4: Be sure when choosing the time constant R1 × C1 that R1 is such that the maximum anticipated output voltage at pin 3 can be reached with I3 × R1. The maximum value for R1 is limited by the output resistance of pin 3 which is greater than 10 MΩ typically. 3 www.national.com LM2907/LM2917 Op Amp/Comparator Power Dissipation LM2907-8, LM2917-8 LM2907-14, LM2917-14 See (Note 1) Operating Temperature Range Storage Temperature Range Soldering Information Dual-In-Line Package Soldering (10 seconds) Small Outline Package Vapor Phase (60 seconds) Infrared (15 seconds) Absolute Maximum Ratings (Note 1) LM2907/LM2917 Note 5: Nonlinearity is defined as the deviation of VOUT (@ pin 3) for fIN = 5 kHz from a straight line defined by the VOUT @ 1 kHz and VOUT @ 10 kHz. C1 = 1000 pF, R1 = 68k and C2 = 0.22 mFd. Test Circuit and Waveform 794206 Tachometer Input Threshold Measurement 794207 www.national.com 4 LM2907/LM2917 Typical Performance Characteristics Tachometer Linearity vs Temperature Tachometer Linearity vs Temperature 794247 794246 Total Supply Current Zener Voltage vs Temperature 794240 794241 Normalized Tachometer Output (K) vs Temperature Normalized Tachometer Output (K) vs Temperature 794243 794242 5 www.national.com LM2907/LM2917 Tachometer Currents I2and I3 vs Supply Voltage Tachometer Currents I2and I3 vs Temperature 794244 794245 Tachometer Linearity vs R1 Tachometer Input Hysteresis vs Temperature 794248 794249 Op Amp Output Transistor Characteristics Op Amp Output Transistor Characteristics 794251 794250 www.national.com 6 The LM2907 series of tachometer circuits is designed for minimum external part count applications and maximum versatility. In order to fully exploit its features and advantages let's examine its theory of operation. The first stage of operation is a differential amplifier driving a positive feedback flipflop circuit. The input threshold voltage is the amount of differential input voltage at which the output of this stage changes state. Two options (LM2907-8, LM2917-8) have one input internally grounded so that an input signal must swing above and below ground and exceed the input thresholds to produce an output. This is offered specifically for magnetic variable reluctance pickups which typically provide a singleended ac output. This single input is also fully protected against voltage swings to ±28V, which are easily attained with these types of pickups. The differential input options (LM2907, LM2917) give the user the option of setting his own input switching level and still have the hysteresis around that level for excellent noise rejection in any application. Of course in order to allow the inputs to attain common-mode voltages above ground, input protection is removed and neither input should be taken outside the limits of the supply voltage being used. It is very important that an input not go below ground without some resistance in its lead to limit the current that will then flow in the epi-substrate diode. Following the input stage is the charge pump where the input frequency is converted to a dc voltage. To do this requires one timing capacitor, one output resistor, and an integrating or filter capacitor. When the input stage changes state (due to a suitable zero crossing or differential voltage on the input) the timing capacitor is either charged or discharged linearly between two voltages whose difference is VCC/2. Then in one half cycle of the input frequency or a time equal to 1/2 fIN the change in charge on the timing capacitor is equal to VCC/2 × C1. The average amount of current pumped into or out of the capacitor then is: CHOOSING R1 AND C1 There are some limitations on the choice of R1 and C1 which should be considered for optimum performance. The timing capacitor also provides internal compensation for the charge pump and should be kept larger than 500 pF for very accurate operation. Smaller values can cause an error current on R1, especially at low temperatures. Several considerations must be met when choosing R1. The output current at pin 3 is internally fixed and therefore VO/R1 must be less than or equal to this value. If R1 is too large, it can become a significant fraction of the output impedance at pin 3 which degrades linearity. Also output ripple voltage must be considered and the size of C2 is affected by R1. An expression that describes the ripple content on pin 3 for a single R1C2 combination is: It appears R1 can be chosen independent of ripple, however response time, or the time it takes VOUT to stabilize at a new voltage increases as the size of C2 increases, so a compromise between ripple, response time, and linearity must be chosen carefully. As a final consideration, the maximum attainable input frequency is determined by VCC, C1 and I2: USING ZENER REGULATED OPTIONS (LM2917) For those applications where an output voltage or current must be obtained independent of supply voltage variations, the LM2917 is offered. The most important consideration in choosing a dropping resistor from the unregulated supply to the device is that the tachometer and op amp circuitry alone require about 3 mA at the voltage level provided by the zener. At low supply voltages there must be some current flowing in the resistor above the 3 mA circuit current to operate the regulator. As an example, if the raw supply varies from 9V to 16V, a resistance of 470Ω will minimize the zener voltage variation to 160 mV. If the resistance goes under 400Ω or over 600Ω the zener variation quickly rises above 200 mV for the same input variation. The output circuit mirrors this current very accurately into the load resistor R1, connected to ground, such that if the pulses of current are integrated with a filter capacitor, then VO = ic × R1, and the total conversion equation becomes: VO = VCC × fIN × C1 × R1 × K Where K is the gain constant—typically 1.0. 7 www.national.com LM2907/LM2917 The size of C2 is dependent only on the amount of ripple voltage allowable and the required response time. Applications Information LM2907/LM2917 Typical Applications Minimum Component Tachometer 794208 ”Speed Switch”, Load is Energized when fIN ≥ (1 / ( 2RC)) 794209 www.national.com 8 LM2907/LM2917 Zener Regulated Frequency to Voltage Converter 794210 Breaker Point Dwell Meter 794211 9 www.national.com LM2907/LM2917 Voltage Driven Meter Indicating Engine RPM VO = 6V @ 400 Hz or 6000 ERPM (8 Cylinder Engine) 794212 Current Driven Meter Indicating Engine RPM IO = 10 mA @ 300 Hz or 6000 ERPM (6 Cylinder Engine) 794213 www.national.com 10 LM2907/LM2917 Capacitance Meter VOUT = 1V–10V for CX = 0.01 to 0.1 mFd (R = 111k) 794214 Two-Wire Remote Speed Switch 794215 11 www.national.com LM2907/LM2917 100 Cycle Delay Switch 794216 Variable Reluctance Magnetic Pickup Buffer Circuits 794239 794217 Precision two-shot output frequency equals twice input frequency. Pulse height = VZENER www.national.com 12 LM2907/LM2917 Finger Touch or Contact Switch 794219 794218 Flashing LED Indicates Overspeed 794220 Flashing begins when fIN ≥ 100 Hz. Flash rate increases with input frequency increase beyond trip point. 13 www.national.com LM2907/LM2917 Frequency to Voltage Converter with 2 Pole Butterworth Filter to Reduce Ripple 794221 Overspeed Latch 794223 794222 www.national.com 14 LM2907/LM2917 Some Frequency Switch Applications May Require Hysteresis in the Comparator Function Which can be Implemented in Several Ways 794224 794225 794226 794227 794228 15 www.national.com LM2907/LM2917 Changing the Output Voltage for an Input Frequency of Zero 794230 794229 Changing Tachometer Gain Curve or Clamping the Minimum Output Voltage 794232 794231 www.national.com 16 LM2907/LM2917 Anti-Skid Circuit Functions “Select-Low” Circuit 794234 VOUT is proportional to the lower of the two input wheel speeds. 794233 “Select-High” Circuit 794236 VOUT is proportional to the higher of the two input wheel speeds. 794235 “Select-Average” Circuit 794237 17 www.national.com *This connection made on LM2907-8 and LM2917-8 only. **This connection made on LM2917 and LM2917-8 only. 794238 LM2907/LM2917 Equivalent Schematic Diagram www.national.com 18 LM2907/LM2917 Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead (0.150″ Wide) Molded Small Outline Package, JEDEC Order Number LM2907M-8 or LM2917M-8 NS Package Number M08A 19 www.national.com LM2907/LM2917 Molded SO Package (M) Order Number LM2907M or LM2917M NS Package Number M14A Molded Dual-In-Line Package (N) Order Number LM2907N-8 or LM2917N-8 NS Package Number N08E www.national.com 20 LM2907/LM2917 Molded Dual-In-Line Package (N) Order Number LM2907N or LM2917N NS Package Number N14A 21 www.national.com LM2907/LM2917 Frequency to Voltage Converter Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Design Support Amplifiers www.national.com/amplifiers WEBENCH® Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage Reference www.national.com/vref Design Made Easy www.national.com/easy PowerWise® Solutions www.national.com/powerwise Solutions www.national.com/solutions Serial Digital Interface (SDI) www.national.com/sdi Mil/Aero www.national.com/milaero Temperature Sensors www.national.com/tempsensors Solar Magic® www.national.com/solarmagic Wireless (PLL/VCO) www.national.com/wireless Analog University® www.national.com/AU THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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