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.