P
RECISION
P
ROGRAMMABLE
R
EFERENCES
LX6431/LX6431A/LX6431B
PRODUCT DATABOOK 1996/1997
7
Copyright © 1999
Rev. 1.4a
P RODUCTION DATA SHEET
The output voltage of the reference can be programmed by using
the formula below:
If more accuracy is required then the effects of the input bias
current (I
REF
) must be taken into account. The formula below
accounts for the error this current produces.
Smaller values of programming resistors tend to minimize bias
current errors. In this respect the low input current characteristics
of the LX6431B helps to reduce the power dissipation on the
programming resistors by a factor of five compared to other
references like the TL1431 and TL431.
The LX6431 series of voltage references have an enhanced
circuit design that can tolerate any value of cathode to anode
capacitance.
APPLICATION INFORMATION
Application Hints
The reference input current of the LX6431 series voltage refer-
ences is much lower than other similar precision parts. This helps
to design programmable voltage references that can use much
higher value programming resistors while maintaining the same
accuracy as the other precision parts. Figure 7 below shows a 5V,
1% shunt regulator using the LX6431B and a shunt regulator using
the TL1431 (Also available from Linfinity). Figure 8 shows 0.5%
shunt regulators. Noteworthy are the values of the reference
resistors used in the two circuits. With the LX6431B it is possible
to use 25k resistors for setting the output voltage with 1%
precision as opposed to 5k programming resistors when the same
precision needs to be achieved with a TL1431.
LX6431B
1k
0.1%
1k
0.1%
R1
R2
GND
a)
V
KA
5V, 0.5%
V
IN
FIGURE 8 — Comparison of reference resistor values between an
LX6431B and a TL1431, when used as 0.5%, 5V shunt regulators.
TL1431
240
0.1%
240
0.1%
R1
R2
GND
b)
V
KA
5V, 0.5%
V
IN
V2.5 1
R1
R2
IR1
KA REF
=∗+
+∗
V2.5 1
R1
R2
KA
≅∗+
LX6431B
25k
0.1%
25k
0.1%
R1
R2
GND
a)
V
KA
5V, 1
V
IN
TL1431
5k
0.1%
5k
0.1%
R1
R2
GND
b)
V
KA
5V, 1
V
IN
FIGURE 7 — Comparison of reference resistor values between an
LX6431B and an TL1431, resistors used with the
LX6431B are 5 times higher in value.
