LM2917| Datasheet

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LM2907/LM2917 Frequency to Voltage Converter

May 2003

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 c
onfigurations 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. n Only one RC network provides frequency doubling n Zener regulator on chip allows accurate and stable frequency to voltage or current conversion (LM2917)

Features
n Ground referenced tachometer input interfaces directly with variable reluctance magnetic pickups n Op amp/comparator has floating transistor output n 50 mA sink or source to operate relays, solenoids, meters, or LEDs n Frequency doubling for low ripple n Tachometer has built-in hysteresis with either differential input or ground referenced input n Built-in zener on LM2917 n 0.3% linearity typical n Ground referenced tachometer is fully protected from damage due to swings above VCC and below ground

Applications
n n n n n n n n n n n 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
n Output swings to ground for zero frequency input n Easy to use; VOUT = fIN x VCC x R1 x C1

Block and Connection Diagrams
Dual-In-Line and Small Outline Packages, Top Views

00794201

00794202

Order Number LM2907M-8 or LM2907N-8 See NS Package Number M08A or N08E

Order Number LM2917M-8 or LM2917N-8 See NS Package Number M08A or N08E

2003 National Semiconductor Corporation

DS007942

www.national.com