LM2907-NFrequency-to-voltage converter
Turn changing speed into a measurable voltage.
LM2907-N converts the rate of an alternating input into an analog voltage. Its input comparator, charge pump and output amplifier form a compact tachometer interface for a magnetic pickup or a suitable test signal. Each complete input cycle transfers a nominal charge of C1 × VCC into the output filter. R1 converts the average current to voltage, while C2 reduces ripple and sets how quickly the reading settles. This reference selects the eight-pin LM2907N-8 and LM2907M-8 packages. Their input must cross ground, and their amplifier positive input is internally joined to the pump output. Fourteen-pin versions have a different pin map; the related LM2917 additionally includes a Zener regulator.
8Physical pins
LM2907N-8/NOPBPDIP-8
Manufacturer-referencedTexas Instruments
Pin diagram
Select a pin to explore its connection
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LM2907-NPDIP-8Top view
LM2907-NSOIC-8Top view
Click a lead or use the arrow keys. Top view
PIN 1 · Tachometer input
Ground-crossing signal inputTACH+
Function
The input comparator detects alternating positive and negative excursions relative to ground.
How to connect
Apply a 1 kHz sine wave with 1 V peak amplitude and zero DC offset in the example.
Electrical note
The eight-pin part needs both polarities; an ordinary 0–5 V logic waveform is not a direct substitute.
PIN 2 · Timing capacitor
Pump timing capacitorCP1
Function
An internal current charges and discharges C1 on alternate input half cycles.
How to connect
Connect C1 = 1 nF to GND.
Electrical note
Keep C1 above 500 pF for accurate operation and internal compensation.
PIN 3 · Averaging network
Filtered charge-pump outputCP2 / IN+
Function
Mirrored current pulses feed R1 and C2. This node is also the amplifier noninverting input in the eight-pin device.
How to connect
Connect 100 kΩ and 1 µF in parallel to GND.
Electrical note
The pump output is a current-producing node, not a rail-to-rail logic signal.
PIN 4 · Buffered output
Output transistor emitterEMIT
Function
Buffered output in the voltage-follower connection.
How to connect
Join to IN−7, a high-impedance voltmeter and a 10 kΩ load to GND.
PIN 5 · Supply
Output transistor collectorCOL
Function
Separate collector of the internal amplifier output transistor.
How to connect
Join to the +12 V supply for the emitter-follower example.
Electrical note
COL is not internally tied to V+.
PIN 6 · Supply
Device supplyV+
Function
Powers the input comparator, charge pump and amplifier.
How to connect
Use a regulated +12 V rail with 100 nF and local bulk bypass to GND.
Electrical note
Conversion gain is proportional to this supply; LM2907 has no LM2917-style internal Zener regulator.
PIN 7 · Amplifier feedback
Amplifier inverting inputIN−
Function
Negative-feedback input for the output amplifier.
How to connect
Connect directly to EMIT4 for unity-gain buffering.
Electrical note
CP2 / IN+3 and IN−7 must remain within the amplifier common-mode region.
PIN 8 · Supply
Ground and input referenceTACH− / GND
Function
Internally connects the negative tachometer input to device ground in the eight-pin variant.
How to connect
Connect externally to circuit GND, including the signal-generator return.
Electrical note
The internal connection does not eliminate the external ground connection.
Key specifications
Both input half cycles contribute charge. The external resistor sets the conversion scale, and the filter capacitor trades ripple against response time.
Bench supply12 V regulated
Example conversion1.2 V / kHz nominal
Selected packages8 pins · PDIP / SOIC
Operating grade−40 to +85 °C
Package details
LM2907N-8/NOPB · PDIP-8
| Property | Details |
|---|---|
| Manufacturer | Texas Instruments |
| Part number | LM2907N-8/NOPB |
| Package | PDIP-8 |
| Connections | 8 pins |
| Mounting | Through-hole |
| Lead pitch | 2.54 mm |
| Package code | PDIP-8 |
| Thermal reference | See operating and package limits |
Operating context
Selected eight-pin devices
Manufacturer specifications 6 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Example supply | 12 V regulated | Datasheet electrical-characteristic test supply |
| Operating temperature | −40 to +85°C | Selected orderable-device grade |
| Amplifier common-mode input | 0 to VCC − 1.5 V | Electrical table at 12 V and 25°C |
| Supply current | 3.8 mA typical; 6 mA maximum | Manufacturer electrical test conditions |
| Supply / collector stress limit | 28 V absolute maximum | Not a normal operating target |
| Storage temperature | −65 to +150°C | Unpowered |
No specifications match. Try a parameter name or a unit.
Supply variation changes the conversion gain; select a clean, stable rail.
Input and charge pump
12 V, 25°C reference conditions
Manufacturer specifications 7 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Input thresholds | ±25 mV typical; ±10 to ±40 mV specified | 250 mV peak-to-peak input at 1 kHz |
| Input hysteresis | 30 mV typical | Manufacturer threshold test |
| Eight-pin input offset | 5 mV typical; 15 mV maximum | Manufacturer threshold test |
| Charge/discharge current | 180 µA typical; 140–240 µA | CP1 / CP2 at 6 V |
| Pump voltage excursion | Approximately VCC / 2 | Difference between C1 charge and discharge levels |
| Conversion constant K | 1 typical; 0.9–1.1 specified | VOUT = K × VCC × f × C1 × R1 |
| C1 selection | Greater than 500 pF for accurate operation | Example uses 1 nF |
No specifications match. Try a parameter name or a unit.
Do not drive the eight-pin input with a waveform that never crosses ground.
Output amplifier
Separate collector and emitter
Manufacturer specifications 6 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Input offset | 3 mV typical; 10 mV maximum | VIN = 6 V |
| Input bias | 50 nA typical; 500 nA maximum | VIN = 6 V |
| Output source current | 10 mA minimum | Emitter at VCC − 2 V |
| Output sink current | 40 mA minimum; 50 mA typical | Collector at 1 V |
| Follower configuration | COL to supply; EMIT to IN− | Example uses a high-impedance meter and 10 kΩ load |
| Example load at 1 kHz | 1.2 V / 10 kΩ = 0.12 mA | Nominal settled value |
No specifications match. Try a parameter name or a unit.
Source and sink capabilities are specified under different conditions; do not assume 50 mA is guaranteed in both directions.
12 V tachometer example
All ground symbols share one return
Manufacturer specifications 8 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| TACH+1 | 1 kHz sine, ±1 V peak | Zero DC offset; generator return to GND8 |
| CP1 pin 2 | C1 = 1 nF to GND | Sets charge transferred per cycle |
| CP2 / IN+ pin 3 | R1 = 100 kΩ and C2 = 1 µF to GND | Parallel averaging network |
| EMIT4 and IN−7 | Join as VOUT | Unity-gain buffer feedback |
| COL5 and V+6 | +12 V | Output transistor and controller share the bench supply |
| GND8 | Circuit return | Mandatory external connection |
| Supply bypass | 100 nF + 10 µF to GND | Close to V+6 and GND8 |
| Output load | 10 kΩ to GND plus voltmeter | Keep the instrument high impedance |
No specifications match. Try a parameter name or a unit.
No microcontroller or firmware is required. This is an illustrative reference circuit, not a live simulation.
Scale, ripple and response
Nominal example · K = 1
Manufacturer specifications 8 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Conversion equation | VOUT ≈ K × VCC × fIN × C1 × R1 | Subject to pump current, amplifier range and tolerances |
| Scale | 1.2 mV / Hz | 12 V × 1 nF × 100 kΩ |
| 500 Hz / 1 kHz / 5 kHz | 0.6 V / 1.2 V / 6 V | Settled illustrative readings |
| Average current at 1 kHz | 12 µA | VCC × fIN × C1 |
| Filter time constant | 100 ms | 100 kΩ × 1 µF |
| Approximate 1% settling | About 0.46 s | 4.6 RC for an ideal first-order filter |
| Pump ripple at 1 kHz | About 5.6 mV peak-to-peak | Datasheet approximation with I2 = 180 µA |
| Stopped input | Output decays toward zero | The filter prevents an instantaneous step |
No specifications match. Try a parameter name or a unit.
These are calculated values. Capacitor/resistor tolerances, K, supply stability and amplifier errors affect the measured result.
Accuracy and design limits
Keep the operating point in range
Manufacturer specifications 6 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Typical linearity | 0.3% | TI test network: C1 = 1 nF, R1 = 68 kΩ, C2 = 0.22 µF |
| Specified nonlinearity | −1% to +1% | 5 kHz deviation from line through 1 and 10 kHz test points |
| Gain error | K is specified 0.9–1.1 | Typical linearity is not total absolute accuracy |
| Larger C2 | Less ripple, slower response | It does not change ideal DC gain |
| Larger R1 or C1 | More volts per hertz | May reduce usable frequency/output range |
| Supply sensitivity | Output scale follows VCC | Use regulation or calibrate the complete system |
No specifications match. Try a parameter name or a unit.
The 100 kΩ example differs from the linearity test network; its total accuracy is not claimed to equal that test result.
Package selection
LM2907N-8/NOPB · PDIP-8
Manufacturer specifications 5 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Through-hole | LM2907N-8/NOPB · PDIP-8 | 2.54 mm pitch; 7.62 mm nominal rows |
| Surface mount | LM2907M-8/NOPB · SOIC-8 | 1.27 mm pitch; narrow body |
| Fourteen-pin variants | Different map and internal connections | Not represented by these eight-pin views |
| LM2917 distinction | Adds an internal Zener regulator | Do not import its regulator limits into LM2907 |
| Footprint provenance | Original editable TEP land patterns | Verify the exact ordered package and fabricator rules |
No specifications match. Try a parameter name or a unit.
Pin functions and physical numbering stay consistent when switching between the two selected packages.
Connections by function
Select a pin for its function, connection guidance and electrical notes.
Tachometer input1 pin
Timing capacitor1 pin
Averaging network1 pin
Buffered output1 pin
Supply3 pins
Amplifier feedback1 pin
Tachometer input1 pin
Timing capacitor1 pin
Averaging network1 pin
Buffered output1 pin
Supply3 pins
Amplifier feedback1 pin
LM2907-N at a glance
Follow the labeled connections and functional stages
How it works
3 stages · Explore one step at a time
Detect the zero crossings
The eight-pin input compares TACH+1 with GND8. Hysteresis rejects small changes close to the crossing.
Transfer and average charge
C1 charges and discharges on alternate half cycles. Both pulses are mirrored into R1 and C2 at pin 3.
Buffer the reading
Connecting EMIT4 to IN−7 makes the amplifier follow the filtered voltage, while COL5 supplies the output transistor.
Step 1 of 3
LM2907-N in a circuit
A regulated supply, one resistor and two conversion capacitors.
Connect it, step by step
Follow the component values and pin connections
Supply both circuits
Join V+6 and COL5 to 12 V; connect ground and local bypass.
Set conversion and filtering
C1 sets the charge per input cycle. R1 sets volts per hertz; C2 smooths the reading.
Measure after settling
At 1 kHz, expect approximately 1.2 V for nominal parts and K = 1. Increase the rate to increase the output.
Inside LM2907-N
Ground-crossing input, charge pump and buffered output.
Explore the circuit
Select a stage to see its role and connections
Recognize each half cycle
The input comparator changes state when the input passes its positive or negative threshold.
Accumulate the charge
Both half-cycle currents contribute to the average at CP2.
Drive the output
The amplifier drives a transistor with separate collector and emitter terminals.
Selected packagePDIP-8LM2907N-8/NOPB
Physical connections8 pinsPackage-specific numbering
Reference collection8 tables46 parameters & pin functions
Pin reference
Signal names, electrical functions and connection guidance
Physical pin numbers8 pins
Scroll within the table to see all columns and rows.
| Pin | Signal | Type | Function & connection |
|---|---|---|---|
| TACH+ | Ground-crossing signal input | The input comparator detects alternating positive and negative excursions relative to ground.Connection guidanceApply a 1 kHz sine wave with 1 V peak amplitude and zero DC offset in the example. The eight-pin part needs both polarities; an ordinary 0–5 V logic waveform is not a direct substitute. | |
| CP1 | Pump timing capacitor | An internal current charges and discharges C1 on alternate input half cycles.Connection guidanceConnect C1 = 1 nF to GND. Keep C1 above 500 pF for accurate operation and internal compensation. | |
| CP2 / IN+ | Filtered charge-pump output | Mirrored current pulses feed R1 and C2. This node is also the amplifier noninverting input in the eight-pin device.Connection guidanceConnect 100 kΩ and 1 µF in parallel to GND. The pump output is a current-producing node, not a rail-to-rail logic signal. | |
| EMIT | Output transistor emitter | Buffered output in the voltage-follower connection.Connection guidanceJoin to IN−7, a high-impedance voltmeter and a 10 kΩ load to GND. | |
| COL | Output transistor collector | Separate collector of the internal amplifier output transistor.Connection guidanceJoin to the +12 V supply for the emitter-follower example. COL is not internally tied to V+. | |
| V+ | Device supply | Powers the input comparator, charge pump and amplifier.Connection guidanceUse a regulated +12 V rail with 100 nF and local bulk bypass to GND. Conversion gain is proportional to this supply; LM2907 has no LM2917-style internal Zener regulator. | |
| IN− | Amplifier inverting input | Negative-feedback input for the output amplifier.Connection guidanceConnect directly to EMIT4 for unity-gain buffering. CP2 / IN+3 and IN−7 must remain within the amplifier common-mode region. | |
| TACH− / GND | Ground and input reference | Internally connects the negative tachometer input to device ground in the eight-pin variant.Connection guidanceConnect externally to circuit GND, including the signal-generator return. The internal connection does not eliminate the external ground connection. |
No pins match these filters. Try another signal name or reset the filters.
Operating context
Selected eight-pin devices
Manufacturer-referenced values6 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Example supply | 12 V regulated | Datasheet electrical-characteristic test supply |
| Operating temperature | −40 to +85°C | Selected orderable-device grade |
| Amplifier common-mode input | 0 to VCC − 1.5 V | Electrical table at 12 V and 25°C |
| Supply current | 3.8 mA typical; 6 mA maximum | Manufacturer electrical test conditions |
| Supply / collector stress limit | 28 V absolute maximum | Not a normal operating target |
| Storage temperature | −65 to +150°C | Unpowered |
No specifications match. Try a parameter name or a unit.
Supply variation changes the conversion gain; select a clean, stable rail.
Input and charge pump
12 V, 25°C reference conditions
Manufacturer-referenced values7 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Input thresholds | ±25 mV typical; ±10 to ±40 mV specified | 250 mV peak-to-peak input at 1 kHz |
| Input hysteresis | 30 mV typical | Manufacturer threshold test |
| Eight-pin input offset | 5 mV typical; 15 mV maximum | Manufacturer threshold test |
| Charge/discharge current | 180 µA typical; 140–240 µA | CP1 / CP2 at 6 V |
| Pump voltage excursion | Approximately VCC / 2 | Difference between C1 charge and discharge levels |
| Conversion constant K | 1 typical; 0.9–1.1 specified | VOUT = K × VCC × f × C1 × R1 |
| C1 selection | Greater than 500 pF for accurate operation | Example uses 1 nF |
No specifications match. Try a parameter name or a unit.
Do not drive the eight-pin input with a waveform that never crosses ground.
Output amplifier
Separate collector and emitter
Manufacturer-referenced values6 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Input offset | 3 mV typical; 10 mV maximum | VIN = 6 V |
| Input bias | 50 nA typical; 500 nA maximum | VIN = 6 V |
| Output source current | 10 mA minimum | Emitter at VCC − 2 V |
| Output sink current | 40 mA minimum; 50 mA typical | Collector at 1 V |
| Follower configuration | COL to supply; EMIT to IN− | Example uses a high-impedance meter and 10 kΩ load |
| Example load at 1 kHz | 1.2 V / 10 kΩ = 0.12 mA | Nominal settled value |
No specifications match. Try a parameter name or a unit.
Source and sink capabilities are specified under different conditions; do not assume 50 mA is guaranteed in both directions.
12 V tachometer example
All ground symbols share one return
Manufacturer-referenced values8 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| TACH+1 | 1 kHz sine, ±1 V peak | Zero DC offset; generator return to GND8 |
| CP1 pin 2 | C1 = 1 nF to GND | Sets charge transferred per cycle |
| CP2 / IN+ pin 3 | R1 = 100 kΩ and C2 = 1 µF to GND | Parallel averaging network |
| EMIT4 and IN−7 | Join as VOUT | Unity-gain buffer feedback |
| COL5 and V+6 | +12 V | Output transistor and controller share the bench supply |
| GND8 | Circuit return | Mandatory external connection |
| Supply bypass | 100 nF + 10 µF to GND | Close to V+6 and GND8 |
| Output load | 10 kΩ to GND plus voltmeter | Keep the instrument high impedance |
No specifications match. Try a parameter name or a unit.
No microcontroller or firmware is required. This is an illustrative reference circuit, not a live simulation.
Scale, ripple and response
Nominal example · K = 1
Manufacturer-referenced values8 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Conversion equation | VOUT ≈ K × VCC × fIN × C1 × R1 | Subject to pump current, amplifier range and tolerances |
| Scale | 1.2 mV / Hz | 12 V × 1 nF × 100 kΩ |
| 500 Hz / 1 kHz / 5 kHz | 0.6 V / 1.2 V / 6 V | Settled illustrative readings |
| Average current at 1 kHz | 12 µA | VCC × fIN × C1 |
| Filter time constant | 100 ms | 100 kΩ × 1 µF |
| Approximate 1% settling | About 0.46 s | 4.6 RC for an ideal first-order filter |
| Pump ripple at 1 kHz | About 5.6 mV peak-to-peak | Datasheet approximation with I2 = 180 µA |
| Stopped input | Output decays toward zero | The filter prevents an instantaneous step |
No specifications match. Try a parameter name or a unit.
These are calculated values. Capacitor/resistor tolerances, K, supply stability and amplifier errors affect the measured result.
Accuracy and design limits
Keep the operating point in range
Manufacturer-referenced values6 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Typical linearity | 0.3% | TI test network: C1 = 1 nF, R1 = 68 kΩ, C2 = 0.22 µF |
| Specified nonlinearity | −1% to +1% | 5 kHz deviation from line through 1 and 10 kHz test points |
| Gain error | K is specified 0.9–1.1 | Typical linearity is not total absolute accuracy |
| Larger C2 | Less ripple, slower response | It does not change ideal DC gain |
| Larger R1 or C1 | More volts per hertz | May reduce usable frequency/output range |
| Supply sensitivity | Output scale follows VCC | Use regulation or calibrate the complete system |
No specifications match. Try a parameter name or a unit.
The 100 kΩ example differs from the linearity test network; its total accuracy is not claimed to equal that test result.
Package selection
LM2907N-8/NOPB · PDIP-8
Manufacturer-referenced values5 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Through-hole | LM2907N-8/NOPB · PDIP-8 | 2.54 mm pitch; 7.62 mm nominal rows |
| Surface mount | LM2907M-8/NOPB · SOIC-8 | 1.27 mm pitch; narrow body |
| Fourteen-pin variants | Different map and internal connections | Not represented by these eight-pin views |
| LM2917 distinction | Adds an internal Zener regulator | Do not import its regulator limits into LM2907 |
| Footprint provenance | Original editable TEP land patterns | Verify the exact ordered package and fabricator rules |
No specifications match. Try a parameter name or a unit.
Pin functions and physical numbering stay consistent when switching between the two selected packages.
No matching rowsTry a pin name, parameter, unit or test condition, or reset the filters.
Speed-to-voltage interface
Convert a magnetic pickup rate into a meter or ADC input.
Manufacturer application guideFrequency monitoring
Observe rate changes with a filtered analog signal.
Manufacturer application guideThreshold detection
Use a suitably configured amplifier stage to detect a selected speed; the example here is a voltage follower.
Manufacturer application guideTake it into ProTech
Find LM2907-N in the Components Library to place its schematic symbol and connect its pins.
Reference page · circuit simulation model not yet availableOpen ProTech