LM331N National Semiconductor, LM331N Datasheet - Page 7

• Manufacturer Part Number: LM331N
• Description: IC, V/F CONVERTER, DIP8, 331
• Manufacturer: National Semiconductor

Specifications of LM331N

• Frequency: 10kHz
• Full Scale Range: 1Hz To 100kHz
• Linearity %: 0.01%
• Supply Voltage Range: 4V To 40V
• Digital Ic Case Style: DIP
• No. Of Pins: 8
• Svhc: No SVHC (15-Dec-2010)
• Operating Temperature Max: 70°C
• Converter Function: VFC
• Full Scale Frequency: 100
• Power Supply Requirement: Single
• Single Supply Voltage (typ): 5/9/12/15/18/24/28V
• Single Supply Voltage (max): 40V
• Single Supply Voltage (min): 4V
• Dual Supply Voltage (typ): Not RequiredV
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Package Type: MDIP
• Bandwidth: 0.1MHz
• Rohs Compliant: Yes
• Converter Type: Voltage/Frequency
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Typical Applications
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.
The output driver transistor acts to saturate pin 3 with an ON
resistance of about 50 . 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
i between 10 µA to 500 µA. It can be used as a voltage ref-
erence for other components, but care must be taken to en-
sure 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 3 plus a few compo-
nents for improved performance.
A resistor, R
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
tor plus a 5 k (cermet, preferably) gain adjust rheostat. The
function of this adjustment is to trim out the gain tolerance of
the LM231/331, and the tolerance of R
For best results, all the components should be stable
low-temperature-coefficient components, such as metal-film
resistors. The capacitor should have low dielectric absorp-
tion; depending on the temperature characteristics desired,
NPO ceramic, polystyrene, PTFE or polypropylene are best
suited.
A capacitor C
for V
cases; however, in cases where better filtering is required, a
IN
. A value of 0.01 µF to 0.1 µF will be adequate in most
IN
IN
= 100 k
is added from pin 7 to ground to act as a filter
S
at pin 2 is made up of a 12 k fixed resis-
±
10%, has been added in the path to
(Continued)
t
, R
DC
L
and C
for all values of
t
.
7
1 µF capacitor can be used. When the RC time constants are
matched at pin 6 and pin 7, a voltage step at V
a step change in f
V
A 47
hysteresis effect which helps the input comparator provide
the excellent linearity (0.03% typical).
DETAIL OF OPERATION OF PRECISION V-TO-F
CONVERTER ( Figure 4 )
In this circuit, integration is performed by using a conven-
tional operational amplifier and feedback capacitor, C
When the integrator’s output crosses the nominal threshold
level at pin 6 of the LM231/331, the timing cycle is initiated.
The average current fed into the op amp’s summing point
(pin 2) is i x (1.1 R
−V
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 con-
verter; nor does the LM231/331 bias current or offset cur-
rent. Instead, the offset voltage and offset current of the op-
erational amplifier are the only limits on how small the signal
can be accurately converted. Since op amps with voltage off-
set well below 1 mV and offset currents well below 2 nA are
available at low cost, this circuit is recommended for best ac-
curacy for small signals. This circuit also responds immedi-
ately to any change of input signal (which a stand-alone cir-
cuit does not) so that the output frequency will be an
accurate representation of V
spacing can be measured.
In the precision mode, excellent linearity is obtained be-
cause the current source (pin 1) is always at ground potential
and that voltage does not vary with V
stand-alone V-to-F converter, a major cause of non-linearity
is the output impedance at pin 1 which causes i to change as
a function of V
The circuit of Figure 5 operates in the same way as Figure 4 ,
but with the necessary changes for high speed operation.
IN
IN
may cause f
/R
IN
resistor, in series with the 1 µF C
. In this circuit, the voltage offset of the LM231/331
IN
OUT
).
OUT
t
C
to stop momentarily.
. If C
t
) x f which is perfectly balanced with
IN
IN
is much less than C
, as quickly as 2 output pulses’
IN
L
, is added to give
or f
OUT
IN
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L
, a step at
will cause
. (In the
F
.