SM73302_15 Datasheet, PDF (20/31 Pages) Texas Instruments – SM73302 88 MHz, Precision, Low Noise, 1.8V CMOS Input, Decompensated Operational Amplifier

SM73302
SNOSB93A – AUGUST 2011 – REVISED APRIL 2013
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Figure 55. LMP7715 Response Gain = +2
The response shown in Figure 54 is close to the response shown in Figure 52. The part is actually slightly faster
in the non-inverting configuration. Decreasing the value of R_C to around 200Ω can decrease the negative
overshoot but will have slightly longer rise and fall times. The other option is to add a small resistor in series with
the input signal. Figure 55 shows the performance of the LMP7715 with no compensation. Again the
decompensated parts are almost 2.5 times faster than the fully compensated op amp.
The most difficult op amp configuration to stabilize is the gain of +1. With proper compensation the SM73302 can
be used in this configuration and still maintain higher speeds than the fully compensated parts. Figure 56 shows
the gain = 1, or the buffer configuration, for these parts.
R_F
-
R_C
R_{P C}
+
Figure 56. SM73302 with Lead-Lag Compensation for Non-Inverting Configuration
Figure 56 is the result of using Equation 8 and additional experimentation in the lab. R_P is not part of Equation 8,
but it is necessary to introduce another pole at the input stage for good performance at gain = +1. Equation 8 is
shown below with R_IN = ∞.
§
¨¨₁
©
+
R_F
R_c
= 18 dB = 7.9
(11)
Using 2 kΩ for R_F and solving for R_C gives R_C = 2000/6.9 = 290Ω. The closest standard value for R_C is 300Ω.
After some fine tuning in the lab R_C = 330Ω and R_P = 1.5 kΩ were chosen as the optimum values. R_P together
with the input capacitance at the non-inverting pin inserts another pole into the compensation for the SM73302.
Adding this pole and slightly reducing the compensation for 1/F (using a slightly higher resistor value for R_C)
gives the optimum response for a gain of +1. Figure 57 is the response of the circuit shown in Figure 56.
Figure 58 shows the response of the LMP7715 in the buffer configuration with no compensation and R_P = R_F = 0.
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