LM2917MXNOPB - NATIONAL SEMICONDUCTOR

December 9, 2008

LM2907/LM2917

Frequency to Voltage Converter

General Description

The LM2907, LM2917 series are monolithic frequency to volt-

age converters with a high gain op amp/comparator designed

to operate a relay, lamp, or other load when the input fre-

quency 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 fre-

quency input.

The op amp/comparator is fully compatible with the tachome-

ter 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 tachome-

ter 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

794202

Order Number LM2917M-8 or LM2917N-8

See NS Package Number M08A or N08E

LM2907/LM2917 Frequency to Voltage Converter

794203

Order Number LM2907M or LM2907N

See NS Package Number M14A or N14A

794204

Order Number LM2917M or LM2917N

See NS Package Number M14A or N14A

Ordering Information

Order

Number

Package

Type

Package

Number

Package

Marking

Supplied

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

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LM2907/LM2917

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

Supply Voltage 28V

Supply Current (Zener Options) 25 mA

Collector Voltage 28V

Differential Input Voltage

Tachometer 28V

Op Amp/Comparator 28V

Input Voltage Range

Tachometer

LM2907-8, LM2917-8 ±28V

LM2907, LM2917 0.0V to +28V

Op Amp/Comparator 0.0V to +28V

Power Dissipation

LM2907-8, LM2917-8 1200 mW

LM2907-14, LM2917-14 1580 mW

See (Note 1)

Operating Temperature Range −40°C to +85°C

Storage Temperature Range −65°C to +150°C

Soldering Information

Dual-In-Line Package

Soldering (10 seconds) 260°C

Small Outline Package

Vapor Phase (60 seconds) 215°C

Infrared (15 seconds) 220°C

Electrical Characteristics

VCC = 12 VDC, TA = 25°C, see test circuit

Symbol Parameter Conditions Min Typ Max Units

TACHOMETER

Input Thresholds VIN = 250 mVp-p @ 1 kHz (Note 2) ±10 ±25 ±40 mV

Hysteresis VIN = 250 mVp-p @ 1 kHz (Note 2) 30 mV

Offset Voltage VIN = 250 mVp-p @ 1 kHz (Note 2)

LM2907/LM2917 3.5 10 mV

LM2907-8/LM2917-8 5 15 mV

Input Bias Current VIN = ±50 mVDC 0.1 1 μA

VOH Pin 2 VIN = +125 mVDC (Note 3) 8.3 V

VOL Pin 2 VIN = −125 mVDC (Note 3) 2.3 V

I2, I3Output Current V2 = V3 = 6.0V (Note 4) 140 180 240 μA

I3Leakage Current I2 = 0, V3 = 0 0.1 μA

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 %

OP/AMP COMPARATOR

VOS VIN = 6.0V 3 10 mV

IBIAS VIN = 6.0V 50 500 nA

Input Common-Mode Voltage 0 VCC−1.5V V

Voltage Gain 200 V/mV

Output Sink Current VC = 1.0 40 50 mA

Output Source Current VE = VCC −2.0 10 mA

Saturation Voltage ISINK = 5 mA 0.1 0.5 V

ISINK = 20 mA 1.0 V

ISINK = 50 mA 1.0 1.5 V

ZENER REGULATOR

Regulator Voltage RDROP = 470Ω 7.56 V

Series Resistance 10.5 15 Ω

Temperature Stability +1 mV/°C

Total Supply Current 3.8 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.

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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

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LM2907/LM2917

Typical Performance Characteristics

Tachometer Linearity

vs Temperature

794246

Tachometer Linearity

vs Temperature

794247

Total Supply Current

794240

Zener Voltage vs

Temperature

794241

Normalized Tachometer Output (K)

vs Temperature

794242

Normalized Tachometer Output (K)

vs Temperature

794243

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LM2907/LM2917

Tachometer Currents I2and I3

vs Supply Voltage

794244

Tachometer Currents I2and I3

vs Temperature

794245

Tachometer Linearity vs R1

794248

Tachometer Input Hysteresis

vs Temperature

794249

Op Amp Output Transistor

Characteristics

794250

Op Amp Output Transistor

Characteristics

794251

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LM2907/LM2917

Applications Information

The LM2907 series of tachometer circuits is designed for

minimum external part count applications and maximum ver-

satility. In order to fully exploit its features and advantages

let's examine its theory of operation. The first stage of oper-

ation is a differential amplifier driving a positive feedback flip-

flop 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 single-

ended 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 lim-

its 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:

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.

The size of C2 is dependent only on the amount of ripple volt-

age allowable and the required response time.

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 in-

ternally 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 lin-

earity. 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 compro-

mise between ripple, response time, and linearity must be

chosen carefully.

As a final consideration, the maximum attainable input fre-

quency 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 reg-

ulator. 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.

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LM2907/LM2917

Typical Applications

Minimum Component Tachometer

794208

”Speed Switch”, Load is Energized when fIN ≥ (1 / ( 2RC))

794209

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LM2907/LM2917

Zener Regulated Frequency to Voltage Converter

794210

Breaker Point Dwell Meter

794211

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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

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LM2907/LM2917

Capacitance Meter

VOUT = 1V–10V for CX = 0.01 to 0.1 mFd

(R = 111k)

794214

Two-Wire Remote Speed Switch

794215

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LM2907/LM2917

100 Cycle Delay Switch

794216

Variable Reluctance Magnetic Pickup Buffer Circuits

794239

Precision two-shot output frequency

equals twice input frequency.

Pulse height = VZENER

794217

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LM2907/LM2917

Finger Touch or Contact Switch

794218

794219

Flashing LED Indicates Overspeed

794220

Flashing begins when fIN ≥ 100 Hz.

Flash rate increases with input frequency

increase beyond trip point.

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LM2907/LM2917

Frequency to Voltage Converter with 2 Pole Butterworth Filter to Reduce Ripple

794221

Overspeed Latch

794222

794223

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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

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LM2907/LM2917

Changing the Output Voltage for an Input Frequency of Zero

794229

794230

Changing Tachometer Gain Curve or Clamping the Minimum Output Voltage

794231

794232

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LM2907/LM2917

Anti-Skid Circuit Functions

“Select-Low” Circuit

794233

794234

VOUT is proportional to the lower

of the two input wheel speeds.

“Select-High” Circuit

794235

794236

VOUT is proportional to the higher

of the two input wheel speeds.

“Select-Average” Circuit

794237

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LM2907/LM2917

Equivalent Schematic Diagram

794238

*This connection made on LM2907-8 and LM2917-8 only.

**This connection made on LM2917 and LM2917-8 only.

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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

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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

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LM2907/LM2917

Molded Dual-In-Line Package (N)

Order Number LM2907N or LM2917N

NS Package Number N14A

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LM2907/LM2917

Notes

LM2907/LM2917 Frequency to Voltage Converter

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