SNAS555C – JUNE 2000 – REVISED MARCH 2013
LM2907/LM2917 Frequency to Voltage Converter
Check for Samples:
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FEATURES
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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
V
CC
and Below Ground
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 V
CC
up to a maximum V
CE
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.
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APPLICATIONS
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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
ADVANTAGES
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Output Swings to Ground For Zero Frequency
Input
Easy to Use; V
OUT
= f
IN
× V
CC
× R1 × C1
Only One RC Network provides Frequency
Doubling
Zener Regulator on Chip allows Accurate and
Stable Frequency to Voltage or Current
Conversion (LM2917)
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Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
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Copyright © 2000–2013, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
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