LM331 [NSC]
Precision Voltage-to-Frequency Converters; 精密电压 - 频率转换器
| 型号： | LM331 |
| 厂家： | 
National Semiconductor |
| 描述： | Precision Voltage-to-Frequency Converters |
| 文件： | 总16页 (文件大小：281K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
December 1994
LM131A/LM131, LM231A/LM231, LM331A/LM331
Precision Voltage-to-Frequency Converters
General Description
The LM131/LM231/LM331 family of voltage-to-frequency
converters are ideally suited for use in simple low-cost cir-
cuits for analog-to-digital conversion, precision frequency-
to-voltage conversion, long-term integration, linear frequen-
cy modulation or demodulation, and many other functions.
The output when used as a voltage-to-frequency converter
is a pulse train at a frequency precisely proportional to the
applied input voltage. Thus, it provides all the inherent ad-
vantages of the voltage-to-frequency conversion tech-
niques, and is easy to apply in all standard voltage-to-fre-
quency converter applications. Further, the LM131A/
LM231A/LM331A attains a new high level of accuracy ver-
sus temperature which could only be attained with expen-
sive voltage-to-frequency modules. Additionally the LM131
is ideally suited for use in digital systems at low power sup-
ply voltages and can provide low-cost analog-to-digital con-
version in microprocessor-controlled systems. And, the fre-
quency from a battery powered voltage-to-frequency con-
verter can be easily channeled through a simple photoisola-
tor to provide isolation against high common mode levels.
has low bias currents without degrading the quick response
necessary for 100 kHz voltage-to-frequency conversion.
And the output is capable of driving 3 TTL loads, or a high
voltage output up to 40V, yet is short-circuit-proof against
V
CC
.
Features
Y
Guaranteed linearity 0.01% max
Y
Improved performance in existing voltage-to-frequency
conversion applications
Y
Split or single supply operation
Y
Operates on single 5V supply
Y
Pulse output compatible with all logic forms
Y
g
Excellent temperature stability, 50 ppm/ C max
§
Y
Y
Low power dissipation, 15 mW typical at 5V
Wide dynamic range, 100 dB min at 10 kHz full scale
frequency
Y
Y
Wide range of full scale frequency, 1 Hz to 100 kHz
Low cost
The LM131/LM231/LM331 utilizes
a new temperature-
compensated band-gap reference circuit, to provide excel-
lent accuracy over the full operating temperature range, at
power supplies as low as 4.0V. The precision timer circuit
Typical Applications
V
R
1
TL/H/5680–1
IN
S
e
f
#
#
OUT
2.09 V
R
R C
t t
L
*Use stable components with low temperature coefficients. See Typical Applications section.
**0.1mF or 1mF, See ‘‘Principles of Operation.’’
FIGURE 1. Simple Stand-Alone Voltage-to-Frequency Converter
e
g
with 0.03% Typical Linearity (f
10 Hz to 11 kHz)
C
1995 National Semiconductor Corporation
TL/H/5680
RRD-B30M115/Printed in U. S. A.
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
LM131A/LM131
40V
LM231A/LM231
40V
LM331A/LM331
40V
Supply Voltage
Output Short Circuit to Ground
Continuous
Continuous
Continuous
Continuous
Continuous
Continuous
Output Short Circuit to V
Input Voltage
CC
b
a
b
a
b
a
0.2V to V
S
0.2V to
V
S
0.2V to
V
S
T
b
T
T
b
T
T
T
MAX
0 C to 70 C
MIN
MAX
MIN
MAX
MIN
a
55 C to 125 C
a
25 C to 85 C
a
Operating Ambient Temperature Range
§
§
§
§
§
§
Power Dissipation (P at 25 C)
§
D
and Thermal Resistance (i
(H Package) P
)
jA
670 mW
D
i
(N Package) P
150 C/W
§
jA
1.25W
1.25W
D
i
(M Package)P
100 C/W
§
1.25W
100 C/W
§
jA
D
i
85 C/W
§
JA
Lead Temperature (Soldering, 10 sec.)
Dual-In-Line Package (Plastic)
Metal Can Package (TO-5)
ESD Susceptibility (Note 4)
Metal Can Package (TO-5)
Other Packages
260 C
§
260 C
§
260 C
§
260 C
§
2000V
500V
500V
e
Electrical Characteristics T 25 C unless otherwise specified (Note 2)
§
A
Parameter
Conditions
Min
Typ
Max
Units
s
s
s
g
g
g
VFC Non-Linearity (Note 3)
4.5V
V
20V
0.003
0.006
0.01
0.02
% Full-
Scale
% Full-
Scale
S
s
g
g
T
T
T
MAX
MIN
A
e
e
10 Hz to 11 kHz
g
VFC Non-Linearity
In Circuit ofFigure 1
V
V
15V, f
0.024
0.14
%Full-
Scale
S
e b
e
14 kX
Conversion Accuracy Scale Factor (Gain)
LM131, LM131A, LM231, LM231A
LM331, LM331A
10V, R
IN
S
0.95
0.90
1.00
1.00
1.05
1.10
kHz/V
kHz/V
s
s
s
s
V 20V
S
Temperature Stability of Gain
LM131/LM231/LM331
LM131A/LM231A/LM331A
T
MIN
T
A
T , 4.5V
MAX
g
g
g
150
30
20
ppm/ C
§
g
50
0.1
0.06
ppm/ C
§
s
s
s
s
Change of Gain with V
4.5V
10V
V
V
10V
40V
0.01
0.006
%/V
%/V
S
S
S
e b
s
Rated Full-Scale Frequency
V
10V
10.0
10
kHz
IN
s
g
Gain Stability vs Time
(1000 Hrs)
T
MIN
T
A
T
MAX
0.02
% Full-
Scale
e b
Overrange (Beyond Full-Scale) Frequency
V
IN
11V
%
INPUT COMPARATOR
g
g
g
g
g
g
Offset Voltage
3
4
3
10
14
10
mV
mV
mV
s
s
s
LM131/LM231/LM331
LM131A/LM231A/LM331A
T
T
T
T
T
T
MIN
MIN
A
A
MAX
MAX
s
s
b
b
g
Bias Current
80
300
100
nA
nA
V
g
Offset Current
8
s
b
b
2.0
Common-Mode Range
T
MIN
T
A
T
MAX
0.2
V
CC
2
e
Electrical Characteristics T 25 C unless otherwise specified (Note 2) (Continued)
§
A
Parameter
Conditions
Min
Typ
Max
Units
TIMER
c
V
S
Timer Threshold Voltage, Pin 5
0.63
0.667
0.70
e
Input Bias Current, Pin 5
All Devices
V
S
0V
15V
s
s
g
200
200
g
V
9.9V
10
100
1000
500
nA
nA
nA
PIN 5
e
e
LM131/LM231/LM331
LM131A/LM231A/LM331A
V
PIN 5
V
PIN 5
10V
10V
e
V
(Reset)
I
5 mA
0.22
0.5
V
SAT PIN 5
CURRENT SOURCE (Pin 1)
e
e
0
Output Current
R
S
14 kX, V
PIN 1
LM131, LM131A, LM231, LM231A
LM331, LM331A
126
116
135
136
144
156
mA
mA
s
s
Change with Voltage
0V
V
PIN 1
10V
0.2
1.0
mA
Current Source OFF Leakage
LM131, LM131A
0.01
0.02
2.0
1.0
10.0
50.0
nA
nA
nA
LM231, LM231A, LM331, LM331A
All Devices
e
T
A
T
MAX
Operating Range of Current (Typical)
(10 to 500)
mA
REFERENCE VOLTAGE (Pin 2)
LM131, LM131A, LM231, LM231A
LM331, LM331A
1.76
1.70
1.89
1.89
2.02
2.08
V
V
DC
DC
g
Stability vs Temperature
Stability vs Time, 1000 Hours
LOGIC OUTPUT (Pin 3)
60
ppm/ C
§
%
g
0.1
e
e
V
I
I
5 mA
3.2 mA (2 TTL Loads), T
0.15
0.10
0.50
0.40
1.0
V
V
mA
SAT
s
s
T
MAX
T
A
MIN
g
OFF Leakage
0.05
SUPPLY CURRENT
e
e
e
e
LM131, LM131A, LM231,
LM231A
LM331, LM331A
V
S
V
S
V
S
V
S
5V
40V
5V
2.0
2.5
1.5
2.0
3.0
4.0
3.0
4.0
4.0
6.0
6.0
8.0
mA
mA
mA
mA
40V
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating
the device beyond its specified operating conditions.
s
s
40V, unless otherwise noted.
Note 2: All specifications apply in the circuit of Figure 3, with 4.0V
V
S
c
b
Note 3: Nonlinearity is defined as the deviation of f
OUT
from V
IN
over the frequency range 1 Hz to 11 kHz. For the timing capacitor, C , use NPO ceramic, Teflon , or polystyrene.
(10 kHz/ 10 V ) when the circuit has been trimmed for zero error at 10 Hz and at 10 kHz,
DC
É
T
Note 4: Human body model, 100 pF discharged through a 1.5 kX resistor.
3
Functional Block Diagram
TL/H/5680–2
Pin numbers apply to 8-pin packages only. See connection diagram for LM231WM pin numbers.
FIGURE 1a
TeflonÉ registered trademark of DuPont
4
Typical Performance Characteristics
(All electrical characteristics apply for the circuit of Figure 3, unless otherwise noted.)
Nonlinearity Error, LM131
Family, as Precision V-to-F
Converter (Figure 3)
Nonlinearity Error, LM131
Family
Nonlinearity vs Power Supply
Voltage
vs
ion
6)
TL/H/5680–3
5
Typical Applications (Continued)
PRINCIPLES OF OPERATION OF A SIMPLIFIED
VOLTAGE-TO-FREQUENCY CONVERTER
DETAIL OF OPERATION, FUNCTIONAL BLOCK
DIAGRAM (FIGURE 1a)
The LM131 is a monolithic circuit designed for accuracy and
versatile operation when applied as a voltage-to-frequency
(V-to-F) converter or as a frequency-to-voltage (F-to-V) con-
verter. A simplified block diagram of the LM131 is shown in
Figure 2 and consists of a switched current source, input
comparator, and 1-shot timer.
The block diagram shows a band gap reference which pro-
vides a stable 1.9 V output. This 1.9 V is well regulated
DC DC
over a V range of 3.9V to 40V. It also has a flat, low tem-
S
perature coefficient, and typically changes less than (/2%
over a 100 C temperature change.
§
The current pump circuit forces the voltage at pin 2 to be at
e
1.90V/R to flow. For
S
The operation of these blocks is best understood by going
through the operating cycle of the basic V-to-F converter,
Figure 2, which consists of the simplified block diagram of
the LM131 and the various resistors and capacitors con-
nected to it.
1.9V, and causes
e
a
current
i
e
R
14k, i 135 mA. The precision current reflector pro-
s
vides a current equal to i to the current switch. The current
switch switches the current to pin 1 or to ground depending
on the state of the R flip-flop.
S
The voltage comparator compares a positive input voltage,
V1, at pin 7 to the voltage, V , at pin 6. If V1 is greater, the
x
comparator will trigger the 1-shot timer. The output of the
timer will turn ON both the frequency output transistor and
The timing function consists of an R flip-flop, and a timer
S
comparator connected to the external R C network. When
t t
the input comparator detects a voltage at pin 7 higher than
pin 6, it sets the R flip-flop which turns ON the current
S
switch and the output driver transistor. When the voltage at
e
the switched current source for a period t 1.1 R C . During
this period, the current i will flow out of the switched current
t
t
pin 5 rises to )/3 V , the timer comparator causes the R
CC
S
e
c
t, into
the capacitor, C . This will normally charge V up to a higher
source and provide a fixed amount of charge, Q
i
flip-flop to reset. The reset transistor is then turned ON and
the current switch is turned OFF.
L
x
level than V1. At the end of the timing period, the current i
will turn OFF, and the timer will reset itself.
However, if the input comparator still detects pin 7 higher
than pin 6 when pin 5 crosses )/3 V , the flip-flop will not
CC
Now there is no current flowing from pin 1, and the capaci-
tor C will be gradually discharged by R until V falls to the
level of V1. Then the comparator will trigger the timer and
start another cycle.
be reset, and the current at pin 1 will continue to flow, in its
attempt to make the voltage at pin 6 higher than pin 7. This
condition will usually apply under start-up conditions or in
the case of an overload voltage at signal input. It should be
noted that during this sort of overload, the output frequency
will be 0; as soon as the signal is restored to the working
range, the output frequency will be resumed.
L
L
x
e
c
c
t
The current flowing into C is exactly I
c
i
(1.1 R C )
L
AVE
f, and the current flowing out of C is exactly V /R
L
t
j
L
x
V
/R . If V is doubled, the frequency will double to main-
IN IN
L
tain this balance. Even a simple V-to-F converter can pro-
vide a frequency precisely proportional to its input voltage
over a wide range of frequencies.
The output driver transistor acts to saturate pin 3 with an
ON resistance of about 50X. In case of overvoltage, the
output current is actively limited to less than 50 mA.
The voltage at pin 2 is regulated at 1.90 V for all values of
DC
i between 10 mA to 500 mA. It can be used as a voltage
reference for other components, but care must be taken to
ensure that current is not taken from it which could reduce
the accuracy of the converter.
PRINCIPLES OF OPERATION OF BASIC VOLTAGE-
TO-FREQUENCY CONVERTER (FIGURE 1)
The simple stand-alone V-to-F converter shown in Figure 1
includes all the basic circuitry of Figure 2 plus a few compo-
nents for improved performance.
e
g
100 kX 10%, has been added in the path
A resistor, R
IN
b
to pin 7, so that the bias current at pin 7 ( 80 nA typical)
will cancel the effect of the bias current at pin 6 and help
provide minimum frequency offset.
The resistance R at pin 2 is made up of a 12 kX fixed
S
resistor plus a 5 kX (cermet, preferably) gain adjust rheo-
stat. The function of this adjustment is to trim out the gain
TL/H/5680–4
FIGURE 2. Simplified Block Diagram of Stand-Alone
Voltage-to-Frequency Converter Showing LM131 and
External Components
tolerance of the LM131, and the tolerance of R , R and C .
t
t
L
6
Typical Applications (Continued)
For best results, all the components should be stable low-
temperature-coefficient components, such as metal-film re-
sistors. The capacitor should have low dielectric absorption;
depending on the temperature characteristics desired, NPO
ceramic, polystyrene, Teflon or polypropylene are best
suited.
The average current fed into the op amp’s summing point
c
c
/R . In this circuit, the voltage offset of the LM131
(pin 2) is i
b
(1.1 R C )
t
f which is perfectly balanced with
t
V
IN IN
input comparator does not affect the offset or accuracy of
the V-to-F converter as it does in the stand-alone V-to-F
converter; nor does the LM131 bias current or offset cur-
rent. Instead, the offset voltage and offset current of the
operational amplifier are the only limits on how small the
signal can be accurately converted. Since op amps with
voltage offset well below 1 mV and offset currents well be-
low 2 nA are available at low cost, this circuit is recommend-
ed for best accuracy for small signals. This circuit also re-
sponds immediately to any change of input signal (which a
stand-alone circuit does not) so that the output frequency
A capacitor C is added from pin 7 to ground to act as a
IN
filter for V . A value of 0.01 mF to 0.1 mF will be adequate in
IN
most cases; however, in cases where better filtering is re-
quired, a 1 mF capacitor can be used. When the RC time
constants are matched at pin 6 and pin 7, a voltage step at
V
will cause a step change in f
. If C is much less
IN
to stop momentarily.
IN
OUT
OUT
than C , a step at V may cause f
L
IN
A 47X resistor, in series with the 1 mF C , is added to give
L
will be an accurate representation of V , as quickly as 2
IN
output pulses’ spacing can be measured.
hysteresis effect which helps the input comparator provide
the excellent linearity (0.03% typical).
In the precision mode, excellent linearity is obtained be-
cause the current source (pin 1) is always at ground poten-
DETAIL OF OPERATION OF PRECISION V-TO-F
CONVERTER (FIGURE 3)
tial and that voltage does not vary with V or f
IN
. (In the
OUT
In this circuit, integration is performed by using a conven-
tional operational amplifier and feedback capacitor, C .
F
stand-alone V-to-F converter, a major cause of non-linearity
is the output impedance at pin 1 which causes i to change
When the integrator’s output crosses the nominal threshold
level at pin 6 of the LM131, the timing cycle is initiated.
as a function of V ).
IN
The circuit ofFigure 4 operates in the same way asFigure 3,
but with the necessary changes for high speed operation.
TL/H/5680–5
*Use stable components with low temperature coefficients. See Typical Applications section.
e
e
4.5V to 8V.
**This resistor can be 5 kX or 10 kX for V
8V to 22V, but must be 10 kX for V
S
S
***Use low offset voltage and low offset current op amps for A1: recommended types LM108, LM308A, LF411A
FIGURE 3. Standard Test Circuit and Applications Circuit, Precision Voltage-to-Frequency Converter
7
Typical Applications (Continued)
DETAILS OF OPERATION, FREQUENCY-TO-
VOLTAGE CONVERTERS(FIGURES 5 AND 6)
0.1 second time constant, and settling of 0.7 second to
0.1% accuracy.
In these applications, a pulse input at f is differentiated by
IN
In the precision circuit, an operational amplifier provides a
buffered output and also acts as a 2-pole filter. The ripple
will be less than 5 mV peak for all frequencies above 1 kHz,
and the response time will be much quicker than inFigure 5.
However, for input frequencies below 200 Hz, this circuit will
have worse ripple thanFigure 5. The engineering of the filter
time-constants to get adequate response and small enough
ripple simply requires a study of the compromises to be
made. Inherently, V-to-F converter response can be fast,
but F-to-V response can not.
a C-R network and the negative-going edge at pin 6 causes
the input comparator to trigger the timer circuit. Just as with
a V-to-F converter, the average current flowing out of pin 1
e
c
c
(1.1 R C )
t
is I
i
f.
AVERAGE
t
In the simple circuit of FIGURE 5, this current is filtered in
e
than 10 mV peak, but the response will be slow, with a
the network R
100 kX and 1 mF. The ripple will be less
L
*Use stable components with low temperature coefficients.
See Typical Applications section.
e
**This resistor can be 5 kX or 10 kX for V
8V to 22V,
S
e
but must be 10 kX for V
4.5V to 8V.
S
***Use low offset voltage and low offset current op amps for A1:
recommended types LF411A or LF356.
TL/H/5680–6
FIGURE 4. Precision Voltage-to-Frequency Converter,
g
100 kHz Full-Scale, 0.03% Non-Linearity
TL/H/5680–7
R
R
R
L
F
e
c
c
c
e b
c
c
c
(R C )
V
OUT
f
2.09V
(R C )
t t
V
f
2.09V
IN
OUT
IN
t t
TL/H/5680–8
R
S
S
b
*Use stable components with low temperature coefficients.
(V
2V)
S
e
SELECT Rx
0.2 mA
*Use stable components with low temperature coefficients.
FIGURE 5. Simple Frequency-to-Voltage Converter,
g
10 kHz Full-Scale, 0.06% Non-Linearity
FIGURE 6. Precision Frequency-to-Voltage Converter,
g
10 kHz Full-Scale with 2-Pole Filter, 0.01%
Non-Linearity Maximum
8
Typical Applications (Continued)
Light Intensity to Frequency Converter
TL/H/5680–9
*L14F-1, L14G-1 or L14H-1, photo transistor (General Electric Co.) or similar
Temperature to Frequency Converter
TL/H/5680–10
Basic Analog-to-Digital Converter Using
Voltage-to-Frequency Converter
Long-Term Digital Integrator Using VFC
TL/H/5680–11
TL/H/5680–12
9
Typical Applications (Continued)
Analog-to-Digital Converter with Microprocessor
TL/H/5680–13
Remote Voltage-to-Frequency Converter with 2-Wire Transmitter and Receiver
TL/H/5680–14
d
Voltage-to-Frequency Converter with Square-Wave Output Using 2 Flip-Flop
TL/H/5680–15
Voltage-to-Frequency Converter with Isolators
TL/H/5680–16
10
Typical Applications (Continued)
Voltage-to-Frequency Converter with Isolators
TL/H/5680–17
Voltage-to-Frequency Converter with Isolators
TL/H/5680–18
Voltage-to-Frequency Converter with Isolators
TL/H/5680–19
11
Connection Diagrams
Metal Can Package
Dual-In-Line Package
TL/H/5680–20
Note: Metal case is connected to pin 4 (GND.)
TL/H/5680–21
Order Number LM131H/883 or LM131AH/883
See NS Package Number H08C
Order Number LM231AN, LM231N, LM331AN,
or LM331N
See NS Package Number N08E
Small-Outline Package
TL/H/5680–24
Top View
Order Number LM231WM
See NS Package Number M14B
12
Schematic Diagram
TL/H/5680–22
13
14
Physical Dimensions inches (millimeters)
Metal Can Package (H)
Order Number LM131H/883 or LM131AH/883
NS Package H08C
14-Pin Small Outline Package (M)
Order Number LM231WM
NS Package M14B
15
Physical Dimensions inches (millimeters) (Continued)
Dual-In-Line Package (N)
Order Number LM231AN, LM231N, LM331AN, or LM331N
NS package N08E
LIFE SUPPORT POLICY
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 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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Corporation
National Semiconductor
Europe
National Semiconductor
Hong Kong Ltd.
National Semiconductor
Japan Ltd.
a
1111 West Bardin Road
Arlington, TX 76017
Tel: 1(800) 272-9959
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(
(
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