LX6431/LX6431A/LX6431B

PRODUCT DA T ABOOK 1996/1997

7

Copyright © 1999

Rev. 1.4a

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

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.

APPLICA TION INFORMA TION

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

+









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.