EL8170, EL8173

12

FN7490.8

August 11, 2015

Submit Document Feedback

.

External Resistor Mismatches

Because of the independent pair of feedback terminals provided

by the EL8170 and EL8173, the CMRR is not degraded by any

resistor mismatches. Hence, unlike a three op amp and

especially a two op amp in-amp, the EL8170 and EL8173 reduce

the cost of external components by allowing the use of 1% or

more tolerance resistors without sacrificing CMRR performance.

The EL8170 and EL8173 CMRR is maintained regardless of the

tolerance of the resistors used.

Gain Error and Accuracy

Specifications” table on page 2 is the inherent gain error of the

EL8170 and EL8173 and does not include the gain error

contributed by the resistors. There is an additional gain error due

to the tolerance of the resistors used. The resulting non-ideal

transfer function effectively becomes Equation 4:

Where:

example, if 1% resistors are used for the EL8170, the total gain

error would be as shown in Equation 5:

Power Dissipation

It is possible to exceed the +150°C maximum junction

temperatures under certain load and power-supply conditions. It

is therefore important to calculate the maximum junction

supply voltages, load conditions, or package type need to be

modified to remain in the safe operating area. These parameters

are related in Equation 6:

where:

Equation 7:

where:

•

1

3

2

8

5

4

7

6

+

-

+

-

IN+

IN-

FB+

FB-

V+

V-

RF

RG

VOUT

EL8170,

VCM

VIN/2

VIN/2

VREF

+2.4V TO +5.5V

EL8173

1

--------

+











+

=

(EQ. 3)

1

--------

+







++



–

 V

IN





=

(EQ. 4)



++





=

0.01 0.01 0.003

++





=

2.3%



=

(EQ. 5)



+

=

(EQ. 6)



----------------------------



+



=

(EQ. 7)