1 Features

1• Ground Referenced Tachometer Input Interfaces

Directly With Variable Reluctance Magnetic

Pickups

• Op Amp 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

• ±0.3% Linearity (Typical)

• Ground-Referenced Tachometer is Fully Protected

From Damage Due to Swings Above VCC and

Below Ground

• Output Swings to Ground For Zero Frequency

Input

• Easy to Use; VOUT = fIN × VCC × R1 × C1

• Zener Regulator on Chip allows Accurate and

Stable Frequency to Voltage or Current

Conversion (LM2917)

2 Applications

• Over- and Under-Speed Sensing

• Frequency-to-Voltage Conversion (Tachometer)

• Speedometers

• Breaker Point Dwell Meters

• Hand-Held Tachometers

• Speed Governors

• Cruise Control

• Automotive Door Lock Control

• Clutch Control

• Horn Control

• Touch or Sound Switches

3 Description

The LM2907 and LM2917 devices are monolithic

frequency-to-voltage converters with a high gain op

amp 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 lowripple,

full-input protection in two versions (8-pin

LM2907 and LM2917), and its output swings to

ground for a zero frequency input.

The op amp 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 28 V.

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 noninverting input. This

version is well suited for single speed or frequency

switching or fully buffered frequency-to-voltage

conversion applications.