LM334H/NOPB National Semiconductor, LM334H/NOPB Datasheet - Page 7

• Manufacturer Part Number: LM334H/NOPB
• Description: IC CURRENT SOURCE ADJ TO46-3
• Manufacturer: National Semiconductor

Specifications of LM334H/NOPB

• Function: Current Source
• Accuracy: ±3%
• Voltage - Input: 1 ~ 40 V
• Current - Output: 10mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Through Hole
• Package / Case: TO-46-3
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Sensing Method: -
• Other names: *LM334H; *LM334H/NOPB; LM334H

Application Hints
The set current (I
uting approximately 50% of the set current, and I
usually included in the I
used for calculations by 5.9%. (See CALCULATING R
The first step is to minimize the tempco of the circuit, using
the following equations. An example is given using a value of
+227µV/˚C as the tempco of the LM134 (which includes the
I
diode (for best results, this value should be directly mea-
sured or obtained from the manufacturer of the diode).
With the R
should be determined to give the desired set current. The
formula for calculating the set current at T = 25˚C is shown
below, followed by an example that assumes the forward
voltage drop across the diode (V
across R
and R
BIAS
component), and −2.5 mV/˚C as the tempco of the
2
/R
1
1
is 67.7mV (64 mV + 5.9% to account for I
1
= 10 (from the previous calculations).
to R
SET
2
ratio determined, values for R
) is the sum of I
1
term by increasing the V
(Continued)
D
) is 0.6V, the voltage
1
and I
FIGURE 3. Zero Tempco Current Source
2
, each contrib-
BIAS
1
. I
R
and R
BIAS
value
BIAS
SET
is
.)
),
2
7
This circuit will eliminate most of the LM134’s temperature
coefficient, and it does a good job even if the estimates of the
diode’s characteristics are not accurate (as the following
example will show). For lowest tempco with a specific diode
at the desired I
tested over temperature. If the measured tempco of I
positive, R
negative, R
for use in this circuit is the 1N457 because its tempco is
centered at 11 times the tempco of the LM134, allowing R
10 R
with non-zero tempcos by setting the tempco component of
the tempco equation to the desired value instead of 0.
EXAMPLE: A 1mA, Zero-Tempco Current Source
First, solve for R
The values of R
resistor values (R
a 0.75% error.
1
. You can also use this circuit to create a current source
00569728
2
2
should be reduced. If the resulting tempco is
should be increased. The recommended diode
SET
1
1
1
and R
and R
, however, the circuit should be built and
= 133Ω and R
2
2
:
can be changed to standard 1%
2
= 1.33kΩ) with less than
www.national.com
SET
2
is
=