
National P/N LM2907 - Frequency to Voltage Converter
LM2907 MDC
Full
production
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tray
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LM2907 MWC
Full
production
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wafer
jar
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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 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.
Features
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Ground referenced tachometer input interfaces directly with variable reluctance magnetic pickups
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Op amp/comparator has floating transistor output
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50 mA sink or source to operate relays, solenoids, meters, or LEDs
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Frequency doubling for low ripple
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Tachometer has built-in hysteresis with either differential input or ground referenced input
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Built-in zener on LM2917
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±0.3% linearity typical
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Ground referenced tachometer is fully protected from damage due to swings above VCC and below
ground
Applications
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