LM2907MEP [NSC]
IC VOLTAGE-FREQUENCY CONVERTER, PDSO14, PLASTIC, SOP-14, Analog Special Function Converter;
| 型号： | LM2907MEP |
| 厂家： | 
National Semiconductor |
| 描述： | IC VOLTAGE-FREQUENCY CONVERTER, PDSO14, PLASTIC, SOP-14, Analog Special Function Converter 转换器 |
| 文件： | 总21页 (文件大小：708K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
May 2003
LM2907/LM2917
Frequency to Voltage Converter
n Only one RC network provides frequency doubling
n Zener regulator on chip allows accurate and stable
frequency to voltage or current conversion (LM2917)
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.
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
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 VCC up to a maximum VCE
of 28V.
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
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.
n
0.3% linearity typical
n Ground referenced tachometer is fully protected from
damage due to swings above VCC and below ground
Applications
n Over/under speed sensing
n Frequency to voltage conversion (tachometer)
n Speedometers
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.
n Breaker point dwell meters
n Hand-held tachometer
n Speed governors
n Cruise control
n Automotive door lock control
n Clutch control
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 Horn control
n Touch or sound switches
Advantages
n Output swings to ground for zero frequency input
n Easy to use; VOUT = fIN x VCC x R1 x C1
Block and Connection Diagrams
Dual-In-Line and Small Outline Packages, Top Views
00794201
Order Number LM2907M-8 or LM2907N-8
See NS Package Number M08A or N08E
00794202
Order Number LM2917M-8 or LM2917N-8
See NS Package Number M08A or N08E
© 2003 National Semiconductor Corporation
DS007942
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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
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2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Power Dissipation
LM2907-8, LM2917-8
LM2907-14, LM2917-14
See (Note 1)
1200 mW
1580 mW
Supply Voltage
28V
25 mA
28V
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)
−40˚C to +85˚C
−65˚C to +150˚C
Supply Current (Zener Options)
Collector Voltage
Differential Input Voltage
Tachometer
28V
28V
260˚C
Op Amp/Comparator
Input Voltage Range
Tachometer
215˚C
220˚C
LM2907-8, LM2917-8
LM2907, LM2917
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.
Op Amp/Comparator
Electrical Characteristics
VCC = 12 VDC, TA = 25˚C, see test circuit
Symbol
Parameter
Conditions
Min
Typ
Max
Units
TACHOMETER
@
Input Thresholds
VIN = 250 mVp-p 1 kHz (Note 2)
10
25
30
40
mV
mV
@
VIN = 250 mVp-p 1 kHz (Note 2)
Hysteresis
@
VIN = 250 mVp-p 1 kHz (Note 2)
Offset Voltage
LM2907/LM2917
LM2907-8/LM2917-8
Input Bias Current
Pin 2
3.5
5
10
15
1
mV
mV
µA
V
VIN
=
50 mVDC
0.1
8.3
2.3
180
VOH
VOL
I2, I3
I3
VIN = +125 mVDC (Note 3)
VIN = −125 mVDC (Note 3)
V2 = V3 = 6.0V (Note 4)
I2 = 0, V3 = 0
Pin 2
V
Output Current
Leakage Current
Gain Constant
Linearity
140
240
0.1
µA
µA
K
(Note 3)
0.9
1.0
0.3
1.1
fIN = 1 kHz, 5 kHz, 10 kHz (Note 5)
−1.0
+1.0
%
OP/AMP COMPARATOR
VOS
VIN = 6.0V
VIN = 6.0V
3
10
mV
nA
V
IBIAS
50
500
Input Common-Mode Voltage
0
V
CC−1.5V
Voltage Gain
200
50
V/mV
mA
mA
V
Output Sink Current
Output Source Current
Saturation Voltage
VC = 1.0
40
VE = VCC −2.0
ISINK = 5 mA
ISINK = 20 mA
ISINK = 50 mA
10
0.1
0.5
1.0
1.5
V
1.0
V
ZENER REGULATOR
Regulator Voltage
RDROP = 470Ω
7.56
10.5
+1
V
Ω
Series Resistance
15
6
Temperature Stability
TOTAL SUPPLY CURRENT
mV/˚C
mA
3.8
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 − (−V ), offset voltage is their difference. See test circuit.
TH
TH
3
1
4
Note 3: V
is equal to
⁄4
x V − 1 V , V is equal to
⁄
x V − 1 V therefore V
− V = V /2. The difference, V
− V , and the mirror gain, I /I ,
OH OL 2 3
OH
CC
BE
OL
CC
BE
OH
OL
CC
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 x R1. The
3
maximum value for R1 is limited by the output resistance of pin 3 which is greater than 10 MΩ typically.
3
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Electrical Characteristics (Continued)
@
@
@
10 kHz. C1 = 1000 pF,
OUT
Note 5: Nonlinearity is defined as the deviation of V
(
pin 3) for f = 5 kHz from a straight line defined by the V
1 kHz and V
OUT
IN
OUT
R1 = 68k and C2 = 0.22 mFd.
Test Circuit and Waveform
00794206
Tachometer Input Threshold Measurement
00794207
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4
Typical Performance Characteristics
Zener Voltage vs
Temperature
Total Supply Current
00794240
00794241
Normalized Tachometer
Output vs Temperature
Normalized Tachometer
Output vs Temperature
00794243
00794242
Tachometer Currents I2
and I3 vs Supply Voltage
Tachometer Currents I2
and I3 vs Temperature
00794244
00794245
5
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Typical Performance Characteristics (Continued)
Tachometer Linearity
vs Temperature
Tachometer Linearity
vs Temperature
00794247
00794246
Tachometer Input Hysteresis
vs Temperature
Tachometer Linearity vs R1
00794249
00794248
Op Amp Output Transistor
Characteristics
Op Amp Output Transistor
Characteristics
00794251
00794250
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6
CHOOSING R1 AND C1
Applications Information
There are some limitations on the choice of R1 and C1 which
should be considered for optimum performance. The timing
capacitor also provides internal compensation for the charge
pump and should be kept larger than 500 pF for very accu-
rate operation. Smaller values can cause an error current on
R1, especially at low temperatures. Several considerations
must be met when choosing R1. The output current at pin 3
is internally fixed and therefore VO/R1 must be less than or
equal to this value. If R1 is too large, it can become a
significant fraction of the output impedance at pin 3 which
degrades linearity. Also output ripple voltage must be con-
sidered and the size of C2 is affected by R1. An expression
that describes the ripple content on pin 3 for a single R1C2
combination is:
The LM2907 series of tachometer circuits is designed for
minimum external part count applications and maximum ver-
satility. In order to fully exploit its features and advantages
let’s examine its theory of operation. The first stage of op-
eration is a differential amplifier driving a positive feedback
flip-flop circuit. The input threshold voltage is the amount of
differential input voltage at which the output of this stage
changes state. Two options (LM2907-8, LM2917-8) have
one input internally grounded so that an input signal must
swing above and below ground and exceed the input thresh-
olds to produce an output. This is offered specifically for
magnetic variable reluctance pickups which typically provide
a single-ended ac output. This single input is also fully
protected against voltage swings to 28V, which are easily
attained with these types of pickups.
The differential input options (LM2907, LM2917) give the
user the option of setting his own input switching level and
still have the hysteresis around that level for excellent noise
rejection in any application. Of course in order to allow the
inputs to attain common-mode voltages above ground, input
protection is removed and neither input should be taken
outside the limits of the supply voltage being used. It is very
important that an input not go below ground without some
resistance in its lead to limit the current that will then flow in
the epi-substrate diode.
It appears R1 can be chosen independent of ripple, however
response time, or the time it takes VOUT to stabilize at a new
voltage increases as the size of C2 increases, so a compro-
mise between ripple, response time, and linearity must be
chosen carefully.
As a final consideration, the maximum attainable input fre-
quency is determined by VCC, C1 and I2:
Following the input stage is the charge pump where the input
frequency is converted to a dc voltage. To do this requires
one timing capacitor, one output resistor, and an integrating
or filter capacitor. When the input stage changes state (due
to a suitable zero crossing or differential voltage on the input)
the timing capacitor is either charged or discharged linearly
between two voltages whose difference is VCC/2. Then in
one half cycle of the input frequency or a time equal to 1/2 fIN
the change in charge on the timing capacitor is equal to
VCC/2 x C1. The average amount of current pumped into or
out of the capacitor then is:
USING ZENER REGULATED OPTIONS (LM2917)
For those applications where an output voltage or current
must be obtained independent of supply voltage variations,
the LM2917 is offered. The most important consideration in
choosing a dropping resistor from the unregulated supply to
the device is that the tachometer and op amp circuitry alone
require about 3 mA at the voltage level provided by the
zener. 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 raw supply
varies from 9V to 16V, a resistance of 470Ω will minimize the
zener voltage variation to 160 mV. If the resistance goes
under 400Ω or over 600Ω the zener variation quickly rises
above 200 mV for the same input variation.
The output circuit mirrors this current very accurately into the
load resistor R1, connected to ground, such that if the pulses
of current are integrated with a filter capacitor, then VO = ic x
R1, and the total conversion equation becomes:
VO = VCC x fIN x C1 x R1 x K
Where K is the gain constant—typically 1.0.
The size of C2 is dependent only on the amount of ripple
voltage allowable and the required response time.
7
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Typical Applications
Minimum Component Tachometer
00794208
00794209
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8
Typical Applications (Continued)
Zener Regulated Frequency to Voltage Converter
00794210
Breaker Point Dwell Meter
00794211
9
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Typical Applications (Continued)
Voltage Driven Meter Indicating Engine RPM
@
VO = 6V 400 Hz or 6000 ERPM (8 Cylinder Engine)
00794212
Current Driven Meter Indicating Engine RPM
@
IO = 10 mA 300 Hz or 6000 ERPM (6 Cylinder Engine)
00794213
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10
Typical Applications (Continued)
Capacitance Meter
VOUT = 1V–10V for CX = 0.01 to 0.1 mFd
(R = 111k)
00794214
Two-Wire Remote Speed Switch
00794215
11
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Typical Applications (Continued)
100 Cycle Delay Switch
00794216
Variable Reluctance Magnetic Pickup Buffer Circuits
00794239
00794217
Precision two-shot output frequency
equals twice input frequency.
Pulse height = V
ZENER
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12
Typical Applications (Continued)
Finger Touch or Contact Switch
00794219
00794218
Flashing LED Indicates Overspeed
00794220
Flashing begins when f ≥ 100 Hz.
IN
Flash rate increases with input frequency
increase beyond trip point.
13
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Typical Applications (Continued)
Frequency to Voltage Converter with 2 Pole Butterworth Filter to Reduce Ripple
00794221
Overspeed Latch
00794223
00794222
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14
Typical Applications (Continued)
Some Frequency Switch Applications May Require Hysteresis in the
Comparator Function Which can be Implemented in Several Ways:
00794224
00794225
00794226
00794227
00794228
15
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Typical Applications (Continued)
Changing the Output Voltage for an Input Frequency of Zero
00794230
00794229
Changing Tachometer Gain Curve or Clamping the Minimum Output Voltage
00794232
00794231
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16
Anti-Skid Circuit Functions
“Select-Low” Circuit
00794234
V
is proportional to the lower of the two input wheel speeds.
OUT
00794233
“Select-High” Circuit
00794236
V
is proportional to the higher of the two input wheel speeds.
OUT
00794235
“Select-Average” Circuit
00794237
17
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Equivalent Schematic Diagram
00794238
*
This connection made on LM2907-8 and LM2917-8 only.
**
This connection made on LM2917 and LM2917-8 only.
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18
Physical Dimensions inches (millimeters)
unless otherwise noted
8-Lead (0.150" Wide) Molded Small Outline Package, JEDEC
Order Number LM2907M-8 or LM2917M-8
NS Package Number M08A
Molded SO Package (M)
Order Number LM2907M or LM2917M
NS Package Number M14A
19
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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
Molded Dual-In-Line Package (N)
Order Number LM2907N-8 or LM2917N-8
NS Package Number N08E
Molded Dual-In-Line Package (N)
Order Number LM2907N or LM2917N
NS Package Number N14A
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20
Notes
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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
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National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
相关型号：
LM2907MX-8/NOPB
IC VOLTAGE-FREQUENCY CONVERTER, PDSO8, 0.150 INCH, PLASTIC, SOIC-8, Analog Special Function Converter
NSC
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