Datasheet

LMV793, LMV794

SNOSAX6D –MARCH 2007–REVISED MARCH 2013

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To summarize, the following steps were taken to compensate the LMV793 for a gain of −1:

1. Values for R

and C were calculated from the Bode plot to give an expected phase margin of 45°. The values

were based on R

= R

= 2 kΩ. These calculations gave R

= 330Ω and C = 390 pF.

2. To reduce the ringing C was increased to 2.2 nF which moved the pole of F, the feedback factor, farther

away from the A

VOL

curve.

3. There was still too much ringing so 2 dB of over-compensation was added to F. This was done by

decreasing R

to 240Ω.

The LMV796 is the fully compensated part which is comparable to the LMV793. Using the LMV796 in the same

setup, but removing the compensation network, provide the response shown in Figure 50 .

Figure 50. LMV796 Response

For large signal response the rise and fall times are dominated by the slew rate of the op amps. Even though

both parts are quite similar the LMV793 will give rise and fall times about 2.5 times faster than the LMV796. This

is possible because the LMV793 is a decompensated op amp and even though it is being used at a gain of −1,

the speed is preserved by using a good technique for external compensation.

Non-Inverting Compensation

For the non-inverting amp the same theory applies for establishing the needed compensation. When setting the

inverting configuration for a gain of −1, F has a value of 2. For the non-inverting configuration both F and the

actual gain are the same, making the non-inverting configuration more difficult to compensate. Using the same

circuit as shown in Figure 44, but setting up the circuit for non-inverting operation (gain of +2) results in similar

performance as the inverting configuration with the inputs set to half the amplitude to compensate for the

additional gain. Figure 51 below shows the results.

Figure 51. R

= 240Ω and C = 2.2 nF, Gain = +2

Product Folder Links: LMV793 LMV794