LM2907, LM2917
FREQUENCY-TO-VOLTAGE CONVERTERS
SLFS011A – MARCH 1986 – REVISED JULY 1993
1
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
D
Output Swings to Ground for
Zero-Frequency Input
D
Only One RC Network Provides Frequency
Doubling for Low Ripple
D
8-Pin Versions Interface Directly to
Variable-Reluctance Magnetic Pickups
D
Uncommitted Collector and Emitter
Outputs Provide 40-mA Sink or Source
Current to Operate Relays, Solenoids,
Meters, or LEDs
D
Built-In Hysteresis for Noise Immunity
D
Linearity Typically ±0.3%
D
8-Pin Versions Are Fully Protected From
Damage Due to TACH Input Swing Above
VCC and Below Ground
applications
Over/under speed sensing
Frequency-to-voltage conversion
Speedometers
Breaker-point dwell meters
Hand-held tachometers
Speed governors
Cruise controls
Automotive door-lock controls
Clutch controls
Horn controls
Touch or sound switches
description
The LM2907 and LM2917 are monolithic frequency-to-voltage converters. Each device has an output circuit
that activates loads such as relays and lamps when the input frequency reaches or exceeds a selected rate.
The converter (tachometer) section consists of a comparator driving a charge pump and offers frequency
doubling for low ripple, full input protection in 8-pin versions, and an output swing to ground for a zero-frequency
input. The output section consists of an operational amplifier, normally operating as a comparator, that drives
an output transistor with both the collector and emitter floating. The circuit can either sink or source 40 mA of
load current.
Two basic configurations are offered: 8-pin devices and 14-pin devices. Each 8-pin version has a ground-
referenced tachometer input and an internal connection between the tachometer output and the operational
amplifier input. The 8-pin versions are suited to single-speed or single-frequency switching or fully buffered
frequency-to-voltage conversion applications. The more versatile 14-pin versions provide differential
tachometer inputs and uncommitted operational amplifier inputs. The tachometer input can be floated, and the
operational amplifier becomes suitable for active filter conditioning of the tachometer output.
The LM2917 has an active shunt regulator connected across the power leads. The regulator clamps the supply
voltage so that stable frequency-to-voltage and frequency-to-current conversions are possible with any supply
voltage and a suitable resistor.
The LM2907 and LM2917 are designed for operation from –40°C to 85°C.
Copyright 1993, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
1
2
3
4
8
7
6
5
TACH+
CAP1
CPO/IN+
E
GND
IN–
VCC
C
LM2907, LM2917 ...D OR P PACKAGE
1
2
3
4
5
6
7
14
13
12
11
10
9
8
TACH+
CAP1
CPO
IN+
E
NC
NC
NC
NC
GND
TACH–
IN–
VCC
C
LM2907, LM2917 ...D OR N PACKAGE
NC – No internal connection
AVAILABLE OPTIONS
–40°C to 85°C
PACKAGED DEVICES
SMALL
OUTLINE
(D)
PLASTIC
DIP
(N)
PLASTIC
DIP
(P)
L2907D8
L2907D14
L2917D8
L2917D14
—
LM2907N
—
LM2917N
LM2907P
—
LM2917P
—
TA
(TOP VIEW)
(TOP VIEW)
LM2907, LM2917
FREQUENCY-TO-VOLTAGE CONVERTERS
SLFS011A – MARCH 1986 – REVISED JULY 1993
2POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
functional block diagrams
CAP1 CPO/IN+
(LM2917 only)
IN–
TACH+
VCC
5
4E
C
3
7
1
6
+
–
8-PIN VERSIONS
Charge
Pump
14-PIN VERSIONS
IN +
(LM2917 only)
IN–
TACH+
VCC
8
5E
C
4
10
1
9
TACH– 11
CPO
3
+
–
CAP1
Charge
Pump
absolute maximum ratings over operating free-air temperature range (unless otherwise noted)†
Supply voltage, VCC: LM2907 28 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Supply current, ICC: LM2917 25 mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Collector-to-emitter voltage 28 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operational amplifier input voltage range, IN+ and IN– 0 V to VCC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tachometer input voltage range: 8-pin version TACH+ 0 V to 28 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14-pin version TACH+ and TACH– 0 V to VCC
. . . . . . . . . . . . . . . . . . . . . . . .
Continuous total dissipation See Dissipation Rating Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating free-air temperature range –40°C to 85°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage temperature range –65°C to 150°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds 260°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
†Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings only , and
functional operation of the device at these or any other conditions beyond those indicated in the recommended operating conditions section of
this specification is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
DISSIPATION RATING TABLE
PACKAGE TA ≤ 25°C
POWER RATING DERATING FACTOR
ABOVE TA = 25°CTA = 85°C
POWER RATING
D (8 pin) 725 mW 5.8 mW/°C377 mW
D (14 pin) 950 mW 7.6 mW/°C 494 mW
N1150 mW 9.2 mW/°C 598 mW
P1000 mW 8.0 mW/°C520 mW
LM2907, LM2917
FREQUENCY-TO-VOLTAGE CONVERTERS
SLFS011A – MARCH 1986 – REVISED JULY 1993
3
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
electrical characteristics, VCC = 12 V (LM2907), V+† = 12 V through 470 Ω (LM2917), TA = 25°C
converter (tachometer) section
PARAMETER
TEST CONDITIONS
LM2907 LM2917
UNIT
PARAMETER
TEST
CONDITIONS
MIN TYP MAX MIN TYP MAX
UNIT
VIT Input threshold voltage VI = 250 mV, f = 1 kHz ±8.5 ±15 ±40 ±8.5 ±15 ±40 mV
Vhys Input hysteresis (see Note 1) VI = 250 mV, f = 1 kHz 30 30 mV
VIO
Input offset voltage 8-pin versions VI = 250 mV, f = 1 kHz 5 15 5 15
mV
V
IO
g
(see Note 1) 14-pin versions VID = 250 mV, f = 1 kHz 3.5 10 3.5 10
mV
IIB Input bias current VI = ±50 mV 0.1 1 0.1 1 µA
VOH High-level output
voltage CAP1 VI or VID = 125 mV 8.3 5 V
VOL Low-level output
voltage CAP1 VI or VID = – 125 mV 2.3 1.2 V
IO
Out
p
ut current
CAP1 CPO
CAP1 and CPO at 6 V 140 200 240
µA
I
O
O
u
tp
u
t
c
u
rrent
CAP1
,
CPO
CAP1 and CPO at 3.8 V 140 200 240 µ
A
Leakage current CPO CAP1 open,
CPO at 0 V,
See Note 3 0.1 0.1 µA
Gain constant 0.9 1 1.1 0.9 1 1.1
Nonlinearity (see Note 2) f = 1 kHz, 5 kHz, or 10 kHz 0.3 ±1 0.3 ±1 %
output section
PARAMETER
TEST CONDITIONS
LM2907 LM2917
UNIT
PARAMETER
TEST
CONDITIONS
MIN TYP MAX MIN TYP MAX
UNIT
VIO
In
p
ut offset voltage
VI = 6 V, See Note 3 3 10
mV
V
IO
Inp
u
t
offset
v
oltage
VI = 3.8 V, See Note 3 3 10
mV
IIB
In
p
ut bias current
VI = 6 V 50 500
nA
I
IB
Inp
u
t
bias
c
u
rrent
VI = 3.8 V 50 500
nA
AVV oltage amplification 200 200 V/mV
ICCollector output (sink) current VC = 1 V, VE = 0 40 50 40 50 mA
IEEmitter output (source) current VC = VCC, VE = VCC –2 –10 –10 mA
IC = 5 mA 0.1 0.5 0.1 0.5
VCE(sat) Collector-emitter saturation voltage IC = 20 mA 1 1 V
()
IC = 50 mA 1 1.5 1 1.5
†V+ is the symbol for voltage applied to a series resistor to create a current source.
NOTES: 1. Hysteresis is the algebraic difference VIT+ – VIT–; offset voltage is the difference in magnitudes |VIT+| – |VIT–|. See parameter
measurement information test circuit.
2. Nonlinearity is defined as the deviation of VO at CPO for f = 5 kHz from a straight line defined by the VO at 1 kHz and VO at 10 kHz,
with C1 = 1000 pF, R1 = 68 Ω, C2 = 0.22 µF.
3. CAP1 must be bypassed with a 0.001-µF capacitor to prevent oscillation for these tests.
LM2907, LM2917
FREQUENCY-TO-VOLTAGE CONVERTERS
SLFS011A – MARCH 1986 – REVISED JULY 1993
4POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
zener regulator (LM2917 only), V+† = 12 V through 470 Ω, TA = 25°C
PARAMETER MIN TYP MAX UNIT
VZRegulated supply voltage 7.56 V
αVZ Temperature coefficient of regulated supply voltage 1 mV/°C
rsSeries resistance 10.5 15 Ω
†V+ is the symbol for voltage applied to a series resistor to create a current source.
total device (LM2907 only), VCC = 12 V, TA = 25°C
PARAMETER MIN TYP MAX UNIT
ICC Supply current 3.8 6 mA
PARAMETER MEASUREMENT INFORMATION
Charge
Pump
C1
TACH+
R1
CAP1 CPO
TEST CIRCUIT
WAVEFORMS
TACH+
CAP1
CPO I × R1 (I ≈ 200 µA)
VOH
VOL
VCC
2
≈ –15 mV≈ 15 mV
Figure 1. Test Circuit and Waveforms
LM2907, LM2917
FREQUENCY-TO-VOLTAGE CONVERTERS
SLFS011A – MARCH 1986 – REVISED JULY 1993
5
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
The LM2907 and LM2917 frequency-to-voltage converter circuits provide maximum versatility with a minimum
of external parts. The first stage of each device is a differential comparator . The single-input 8-pin versions have
one input grounded so that an input signal must swing above and below GND and exceed the input thresholds
to produce an output. This version is specifically for magnetic variable-reluctance pickups, which typically
provide a single-ended ac output. These single-ended inputs are fully protected against voltage swings to
±28 V, which are easily attained by this type of pickup.
The differential-input 14-pin versions provide the option of setting the input reference level, maintaining
hysteresis around that level to provide excellent noise rejection in any application. The input protection is
removed in the 14-pin versions. Therefore, neither of the differential inputs should exceed the limits of the supply
voltage. An input must not go below GND without a resistance in the lead to limit the current that flows in the
episubstrate diode. The charge-pump circuit that follows the input state produces a dc output voltage
proportional to the input frequency . The charge-pump circuit (see Figures 1 and 2) consists of a timing capacitor
(C1), an output resistor (R1), and an integrating or filter capacitor (C2). When the input changes state (due to
a suitable zero crossing or differential voltage on the input), the timing capacitor is either charged or discharged
linearly with a constant current of 200 µA through CAP1 between two voltages whose difference is VCC/2. Within
one-half cycle of the input frequency or a time equal to 1/2f, the change in charge on C1 is equal to (VCC/2)C1.
The average amount of current pumped into or out of the capacitor is:
CAP1 current (average)
+
Q
T
+
C1 •VCC
2•2f
+
VCC •f•C1
The output of the charge pump accurately mirrors the CAP1 current into the load resistor (R1) connected to
CPO. If the pulses of current are integrated with a filter capacitor, the output voltage is the average CAP1 current
times R1 and the total equation becomes:
VO
+
VCC •f•C1 •R1 •K
where K is the gain factor, which is typically one.
The size of C2 is dependent only on the amount of ripple allowable and the required response time.
selection of R1, C1, and C2
To achieve optimum performance, there are some limitations to be considered in the selection of R1 and C1.
The timing capacitor controls the RC time and provides internal compensation for the charge-pump circuit. For
very accurate operation, it should be 100 pF or greater. Smaller values, especially at lower temperatures, can
cause an error current through R1. VO/R1 must be less than or equal to the output current at CPO, which is fixed
typically at 200 µA. If R1 is too large, it becomes a significant fraction of the output impedance at CPO, which
degrades the linearity. In addition, ripple voltage must be considered when selecting R1. The size of C2 is
directly affected by the size of R1. An expression that describes the ripple content at CPO is:
Vripple
+
VCC
2C1
C2 (1
*
VCC fC1
200 )
•••volts peak-to-peak•
where:
C1 and C2 are in farads,
VCC is in volts, and
f is in hertz.
LM2907, LM2917
FREQUENCY-TO-VOLTAGE CONVERTERS
SLFS011A – MARCH 1986 – REVISED JULY 1993
6POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
R1 cannot be chosen independent of ripple because response time or the time it takes VO to stabilize at a new
level increases as the size of C2 increases. A compromise between ripple, response time, and linearity must
be chosen carefully. As a final consideration, the maximum attainable input frequency is determined by VCC,
C1, and Icap (current through CAP1).
fmax
+
Icap
C1 VCC hertz
•
where:
Icap is typically 200 µA,
C1 is in farads, and
VCC is in volts.
zener regulator options (LM2917)
For those applications in which an output voltage or current must be obtained independent of supply voltage
variations, the LM2917 can be used. The most important factor in selecting a dropping resistor for the
unregulated supply is that the frequency-to-voltage converter circuit and the operational amplifier alone require
approximately 3 mA at the voltage level set by the zener diode. At low supply voltages, there must be some
current flowing in the resistor above the 3-mA circuit current to operate the regulator. As an example, if the supply
voltage varies between 9 V and 16 V, a resistance of 470 Ω minimizes the zener voltage variation to typically
160 mV. If the resistance goes under 400 Ω or above 600 Ω, the zener variation quickly rises above 200 mV
for the same input variation.
Charge
Pump
C1
TACH+
R1
CAP1 IN–
10 kΩ
VCC
C2
CAPO/IN+ Emitter/Follower
Output
E
+
–
Figure 2. Minimum-Component Tachometer
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