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LM2907/LM2917 Frequency to Voltage Converter
May 2003
LM2907/LM2917
Frequency to Voltage Converter
General Description
The LM2907, LM2917 series are monolithic frequency to
voltage converters with a high gain op amp/comparator de-
signed to operate a relay, lamp, or other load when the input
frequency reaches or exceeds a selected rate. The tachom-
eter 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 tachom-
eter 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 ta-
chometer 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 tachom-
eter 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.
n
Only one RC network provides frequency doubling
n
Zener regulator on chip allows accurate and stable
frequency to voltage or current conversion (LM2917)
Features
n
Ground referenced tachometer input interfaces directly
with variable reluctance magnetic pickups
n
Op amp/comparator has floating transistor output
n
50 mA sink or source to operate relays, solenoids,
meters, or LEDs
n
Frequency doubling for low ripple
n
Tachometer has built-in hysteresis with either differential
input or ground referenced input
n
Built-in zener on LM2917
n
±
0.3% linearity typical
n
Ground referenced tachometer is fully protected from
damage due to swings above V
CC
and below ground
Applications
n
n
n
n
n
n
n
n
n
n
n
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
Advantages
n
Output swings to ground for zero frequency input
n
Easy to use; V
OUT
= f
IN
x V
CC
x R1 x C1
Block and Connection Diagrams
Dual-In-Line and Small Outline Packages, Top Views
00794201
00794202
Order Number LM2907M-8 or LM2907N-8
See NS Package Number M08A or N08E
Order Number LM2917M-8 or LM2917N-8
See NS Package Number M08A or N08E
© 2003 National Semiconductor Corporation
DS007942
www.national.com
LM2907/LM2917
Block and Connection Diagrams
Dual-In-Line and Small Outline Packages, Top Views
(Continued)
00794203
00794204
Order Number LM2907M or LM2907N
See NS Package Number M14A or N14A
Order Number LM2917M or LM2917N
See NS Package Number M14A or N14A
www.national.com
2
LM2907/LM2917
Absolute Maximum Ratings
(Note 1)
Power Dissipation
LM2907-8, LM2917-8
LM2907-14, LM2917-14
See (Note 1)
Operating Temperature Range
Storage Temperature Range
Soldering Information
Dual-In-Line Package
Soldering (10 seconds)
Small Outline Package
Vapor Phase (60 seconds)
Infrared (15 seconds)
215˚C
220˚C
260˚C
−40˚C to +85˚C
−65˚C to +150˚C
1200 mW
1580 mW
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage
Supply Current (Zener Options)
Collector Voltage
Differential Input Voltage
Tachometer
Op Amp/Comparator
Input Voltage Range
Tachometer
LM2907-8, LM2917-8
LM2907, LM2917
Op Amp/Comparator
28V
28V
28V
25 mA
28V
±
28V
0.0V to +28V
0.0V to +28V
See AN-450 “Surface Mounting Methods and Their Effect
on Product Reliability” for other methods of soldering
surface mount devices.
Electrical Characteristics
V
CC
= 12 V
DC
, T
A
= 25˚C, see test circuit
Symbol
TACHOMETER
Input Thresholds
Hysteresis
Offset Voltage
LM2907/LM2917
LM2907-8/LM2917-8
Input Bias Current
V
OH
V
OL
I
2
, I
3
I
3
K
Pin 2
Pin 2
Output Current
Leakage Current
Gain Constant
Linearity
OP/AMP COMPARATOR
V
OS
I
BIAS
Input Common-Mode Voltage
Voltage Gain
Output Sink Current
Output Source Current
Saturation Voltage
V
C
= 1.0
V
E
= V
CC
−2.0
I
SINK
= 5 mA
I
SINK
= 20 mA
I
SINK
= 50 mA
ZENER REGULATOR
Regulator Voltage
Series Resistance
Temperature Stability
TOTAL SUPPLY CURRENT
R
DROP
= 470Ω
7.56
10.5
+1
3.8
6
15
V
Ω
mV/˚C
mA
1.0
40
V
IN
= 6.0V
V
IN
= 6.0V
0
200
50
10
0.1
0.5
1.0
1.5
3
50
10
500
V
CC
−1.5V
mV
nA
V
V/mV
mA
mA
V
V
V
V
IN
=
±
50 mV
DC
V
IN
= +125 mV
DC
(Note 3)
V
IN
= −125 mV
DC
(Note 3)
V2 = V3 = 6.0V (Note 4)
I2 = 0, V3 = 0
(Note 3)
f
IN
= 1 kHz, 5 kHz, 10 kHz (Note 5)
0.9
−1.0
1.0
0.3
140
V
IN
= 250 mVp-p
@
1 kHz (Note 2)
V
IN
= 250 mVp-p
@
1 kHz (Note 2)
V
IN
= 250 mVp-p
@
1 kHz (Note 2)
3.5
5
0.1
8.3
2.3
180
240
0.1
1.1
+1.0
%
10
15
1
mV
mV
µA
V
V
µA
µA
Parameter
Conditions
Min
Typ
Max
Units
mV
mV
±
10
±
25
30
±
40
Note 1:
For operation in ambient temperatures above 25˚C, the device must be derated based on a 150˚C maximum junction temperature and a thermal resistance
of 101˚C/W junction to ambient for LM2907-8 and LM2917-8, and 79˚C/W junction to ambient for LM2907-14 and LM2917-14.
Note 2:
Hysteresis is the sum +V
TH
− (−V
TH
), offset voltage is their difference. See test circuit.
Note 3:
V
OH
is equal to
3
⁄
4
x V
CC
− 1 V
BE
, V
OL
is equal to
1
⁄
4
x V
CC
− 1 V
BE
therefore V
OH
− V
OL
= V
CC
/2. The difference, V
OH
− V
OL
, and the mirror gain, I
2
/I
3
,
are the two factors that cause the tachometer gain constant to vary from 1.0.
Note 4:
Be sure when choosing the time constant R1 x C1 that R1 is such that the maximum anticipated output voltage at pin 3 can be reached with I
3
x R1. The
maximum value for R1 is limited by the output resistance of pin 3 which is greater than 10 MΩ typically.
3
www.national.com
LM2907/LM2917
Electrical Characteristics
(Continued)
Note 5:
Nonlinearity is defined as the deviation of V
OUT
(
@
pin 3) for f
IN
= 5 kHz from a straight line defined by the V
OUT
@
1 kHz and V
OUT
@
10 kHz. C1 = 1000 pF,
R1 = 68k and C2 = 0.22 mFd.
Test Circuit and Waveform
00794206
Tachometer Input Threshold Measurement
00794207
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