LM231N National Semiconductor, LM231N Datasheet - Page 8

• Manufacturer Part Number: LM231N
• Description: Voltage / Frequency (V/F & F/V) Converter IC
• Manufacturer: National Semiconductor

Specifications of LM231N

• Frequency: 100kHz
• No. Of Pins: 8
• Mounting Type: Through Hole
• Converter Type: Voltage/Frequency
• Operating Temperature Max: 85°C
• Peak Reflow Compatible (260 C): No
• 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): -25C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Commercial
• Package Type: MDIP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Applications Information
A 47Ω resistor, in series with the 1 µF C
esis, which helps the input comparator provide the excellent
linearity.
*Use stable components with low temperature coefficients. See Typical
Applications section.
**0.1µF or 1µF, See “Principles of Operation.”
*Use stable components with low temperature coefficients. See Typical Applications section.
**This resistor can be 5 kΩ or 10 kΩ for V
***Use low offset voltage and low offset current op-amps for A1: recommended type LF411A
with
FIGURE 3. Simple Stand-Alone V-to-F Converter
±
0.03% Typical Linearity (f = 10 Hz to 11 kHz)
FIGURE 4. Standard Test Circuit and Applications Circuit, Precision Voltage-to-Frequency Converter
S
=8V to 22V, but must be 10 kΩ for V
L
, provides hyster-
(Continued)
00568001
8
S
=4.5V to 8V.
Details of Operation: 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
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 below
2 nA are available at low cost, this circuit is recommended for
best accuracy for small signals. This circuit also responds
immediately to any change of input signal (which a stand-
alone circuit 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
/R
IN
. In this circuit, the voltage offset of the LM231/331
IN
).
t
C
00568005
t
) x f which is perfectly balanced with
IN
, as quickly as 2 output pulses’
IN
or f
OUT
. (In the
F
.