LMP7718MAE/NOPB National Semiconductor, LMP7718MAE/NOPB Datasheet - Page 16

• Manufacturer Part Number: LMP7718MAE/NOPB
• Description: IC OP AMP PREC DUAL 88MHZ 8-SOIC
• Manufacturer: National Semiconductor
• Series: LMP®, PowerWise®r

Specifications of LMP7718MAE/NOPB

• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Slew Rate: 35 V/µs
• Gain Bandwidth Product: 88MHz
• Current - Input Bias: 0.1pA
• Voltage - Input Offset: 10µV
• Current - Supply: 1.3mA
• Current - Output / Channel: 60mA
• Voltage - Supply, Single/dual (±): 1.8 V ~ 5.5 V, ±0.9 V ~ 2.75 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Other names: LMP7718MAE

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Some over-compensation appears to be needed for the de-
sired overshoot characteristics. Instead of intersecting the
A
and the A
tion 5 for 20 dB, or 10 V/V, the closest standard value of R
is 240Ω. The following two waveforms show the new resistor
value with C = 390 pF and 2.2 nF.
compensation and a very good response for the 1 MHz
square wave.
VOL
FIGURE 6. First Try at Compensation, Gain = −1
curve at 18 dB, 2 dB of over-compensation will be used,
FIGURE 7. C Increased to 2.2 nF, Gain = −1
VOL
curve will be intersected at 20 dB. Using Equa-
Figure 9
shows the final
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C
16
To summarize, the following steps were taken to compensate
the LMP7717 for a gain of −1:
1.
2.
3.
The LMP7715 is the fully compensated part which is compa-
rable to the LMP7717. Using the LMP7715 in the same setup,
but removing the compensation network, provided the re-
sponse shown in
Values for R
to give an expected phase margin of 45°. The values
were based on R
R
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
There was still too much ringing so 2 dB of over-
compensation was added to F. This was done by
decreasing R
FIGURE 8. R
FIGURE 9. R
c
= 330Ω and C = 390 pF.
VOL
c
Figure 10
C
C
C
and C were calculated from the Bode plot
curve.
to 240Ω.
= 240Ω and C = 390 pF, Gain = −1
= 240Ω and C = 2.2 nF, Gain = −1
IN
= R
F
.
= 2 kΩ. These calculations gave
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