PLMP7704HBHSLASHEM datasheet(19/31 Pages) TI

19 / 31 page

As shown in Equation 2, as values of R1 and R2 are increased, the magnitude of the poles is reduced, which in

turn decreases the bandwidth of the amplifier. Whenever possible, best practice is to choose smaller feedback

resistors. Figure 7-3 shows the effect of the feedback resistor on the bandwidth of the LMP7704-SP.

10k

100k

10M

FREQUENCY (Hz)

-10

-8

-6

-4

-2

VS = 5V

CF = 0 pF

AV = -1

R1 = R2 = 100 k:

R1 = R2 = 30 k:

R1 = R2 = 10 k:

R1 = R2 = 1 k:

Figure 7-3. Closed-Loop Gain vs Frequency

Equation 2 has two poles. In most cases, it is the presence of pairs of poles that causes gain peaking. To

eliminate this effect, the poles should be placed in Butterworth position, because poles in Butterworth position do

not cause gain peaking. To achieve a Butterworth pair, the quantity under the square root in Equation 2 should

be set to equal −1. Using this fact and the relation between R1 and R2, R2 = −AV R1, the optimum value for R1

can be found. This is shown in Equation 3. If R1 is chosen to be larger than this optimum value, gain peaking will

occur.

(1 - AV)

2A0AVCIN

(3)

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LMP7704-SP

SNOSDB6A – DECEMBER 2020 – REVISED JANUARY 2021

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PLMP7704HBH/EM Datasheet(PDF) 19 Page - Texas Instruments