LMP8602MM datasheet(17/24 Pages) NSC

17 / 24 page

r creates a resistive divider together with the internal

100 k

Ω resistor such that, for the LMP8602, the reduced gain

r becomes:

For the LMP8603:

Given a desired value of the reduced gain G

r, using this equa-

tion the required value for R

r can be calculated for the

LMP8602 with:

and for the LMP8603 with:

Increase Gain

Figure 4 shows the configuration that can be used to increase

the gain of the LMP8602/LMP8602Q/LMP8603/LMP8603Q.

i creates positive feedback from the output pin to the input

of the buffer amplifier. The positive feedback increases the

gain. The increased gain G

i for the LMP8602 becomes:

and for the LMP8603:

From this equation, for a desired value of the gain, the re-

quired value of R

i can be calculated for the LMP8602 with:

and for the LMP8603 with:

It should be noted from the equation for the gain G

i that for

large gains R

i approaches 100 kΩ. In this case, the denomi-

nator in the equation becomes close to zero. In practice, for

large gains the denominator will be determined by tolerances

in the value of the external resistor R

i and the internal 100

Ω resistor. In this case, the gain becomes very inaccurate. If

the denominator becomes equal to zero, the system will even

become instable. It is recommended to limit the application of

this technique to gain increases of a factor 2.5 or smaller.

30083457

FIGURE 4. Increase Gain

LMP8602MM Arkusz danych(PDF) 17 Page - National Semiconductor (TI)