LM2917

Contents

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.

• 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

• 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