Datasheet LM2907N-NOPB Specification

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; V

■

= fIN × VCC × R1 × C1

OUT

■

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Features

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Applications

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LM2907/LM2917 Frequency to Voltage Converter

December 9, 2008

Only one RC network provides frequency doubling
Zener regulator on chip allows accurate and stable

frequency to voltage or current conversion (LM2917)

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

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

Order Number LM2907M-8 or LM2907N-8

See NS Package Number M08A or N08E

© 2008 National Semiconductor Corporation 7942 www.national.com

794201

Order Number LM2917M-8 or LM2917N-8

See NS Package Number M08A or N08E

794202

LM2907/LM2917

Order Number LM2907M or LM2907N

See NS Package Number M14A or N14A

794203

Order Number LM2917M or LM2917N

See NS Package Number M14A or N14A

Ordering Information

Order

Number

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

Package

Type

Package

Number

Package

Marking

794204

Supplied

As

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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

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

LM2907, LM2917 0.0V to +28V

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 mV

V

V

I2, I

I

3

OH

OL

3

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

Pin 2 VIN = −125 mVDC (Note 3) 2.3 V

Output Current V2 = V3 = 6.0V (Note 4) 140 180 240

Leakage Current I2 = 0, V3 = 0 0.1

DC

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

V

I

BIAS

OS

VIN = 6.0V 3 10 mV

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 I

= 5 mA 0.1 0.5 V

SINK

I

= 20 mA 1.0 V

SINK

I

= 50 mA 1.0 1.5 V

SINK

ZENER REGULATOR

Regulator Voltage

R

DROP

= 470Ω

Series Resistance 10.5 15

Temperature Stability +1 mV/°C

Total Supply Current 3.8 6 mA

0.1 1

7.56 V

μA

μA

μA

Ω

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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Note 5: Nonlinearity is defined as the deviation of V
1000 pF, R1 = 68k and C2 = 0.22 mFd.

Test Circuit and Waveform

LM2907/LM2917

(@ pin 3) for fIN = 5 kHz from a straight line defined by the V

OUT

Tachometer Input Threshold Measurement

@ 1 kHz and V

OUT

794206

@ 10 kHz. C1 =

OUT

794207

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Typical Performance Characteristics

LM2907/LM2917

Tachometer Linearity

vs Temperature

Total Supply Current

794246

Tachometer Linearity

vs Temperature

794247

Zener Voltage vs

Temperature

794240

Normalized Tachometer Output (K)

vs Temperature

794242

794241

Normalized Tachometer Output (K)

vs Temperature

794243

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LM2907/LM2917

Tachometer Currents I2and I

vs Supply Voltage

3

Tachometer Currents I2and I

vs Temperature

3

Tachometer Linearity vs R1

Op Amp Output Transistor

Characteristics

794244

794248

794245

Tachometer Input Hysteresis

vs Temperature

794249

Op Amp Output Transistor

Characteristics

794250

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794251

LM2907/LM2917

Applications Information

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:

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 volt­age 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 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 V
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.

to stabilize at a new

OUT

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Typical Applications

LM2907/LM2917

Minimum Component Tachometer

794208

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

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794209

Zener Regulated Frequency to Voltage Converter

Breaker Point Dwell Meter

LM2907/LM2917

794210

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)

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794213

LM2907/LM2917

V

= 1V–10V for CX = 0.01 to 0.1 mFd

OUT

(R = 111k)

Two-Wire Remote Speed Switch

Capacitance Meter

794214

794215

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LM2907/LM2917

100 Cycle Delay Switch

794216

Variable Reluctance Magnetic Pickup Buffer Circuits

Precision two-shot output frequency

equals twice input frequency.

Pulse height = V

ZENER

794239

794217

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Finger Touch or Contact Switch

LM2907/LM2917

794219

794218

Flashing LED Indicates Overspeed

Flashing begins when fIN ≥ 100 Hz.

Flash rate increases with input frequency

increase beyond trip point.

794220

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LM2907/LM2917

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

794221

Overspeed Latch

794223

794222

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Some Frequency Switch Applications May Require Hysteresis in the Comparator Function Which can be Implemented in Several Ways

LM2907/LM2917

794225

794224

794226

794227

794228

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Changing the Output Voltage for an Input Frequency of Zero

LM2907/LM2917

794229

Changing Tachometer Gain Curve or Clamping the Minimum Output Voltage

794230

794231

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794232

Anti-Skid Circuit Functions

“Select-Low” Circuit

LM2907/LM2917

“Select-High” Circuit

794233

794235

V

is proportional to the lower

OUT

of the two input wheel speeds.

V

is proportional to the higher

OUT

of the two input wheel speeds.

794234

794236

“Select-Average” Circuit

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794237

Equivalent Schematic Diagram

LM2907/LM2917

794238

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

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

Physical Dimensions inches (millimeters) unless otherwise noted

LM2907/LM2917

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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Notes

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