LMP7717MF/NOPB National Semiconductor, LMP7717MF/NOPB Datasheet - Page 20

• Manufacturer Part Number: LMP7717MF/NOPB
• Description: IC OP AMP PREC LN 88MHZ SOT23-5
• Manufacturer: National Semiconductor
• Series: LMP®, PowerWise®r

Specifications of LMP7717MF/NOPB

• Amplifier Type: General Purpose
• Number Of Circuits: 1
• 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: 1.15mA
• 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: SOT-23-5, SC-74A, SOT-25
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Other names: LMP7717MFTR

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After a bit of algebraic manipulation the above equation re-
duces to:
In the above equation the only unknown is C
solve this equation the fourth power of C
An excel spread sheet with this equation can be used and all
the known values entered. Then through iteration, the value
of C
correct value for C
is used for C
Before moving to the lab, the transfer function of the tran-
simpedance amplifier must be found and the units must be in
Ohms.
The LMP7717 was evaluated for R
representing a somewhat lower gain configuration and with
the 100 kΩ feedback resistor a fairly high gain configuration.
The R
Mode Capacitance vs. V
point selected C
2.5V, C
culated value is 1.75 pF, so 1.8 pF is selected for use.
Checking the frequency of the pole finds that it is at 8.8 MHz,
which is right at the minimum gain recommended for this part.
Some over compensation was necessary for stability and the
final selected value for C
5.9 MHz.
obtained in the lab with a 1V output swing. The laser diode
was difficult to drive due to thermal effects making the starting
and ending point of the pulse quite different, therefore the two
separate scope pictures.
F
F
when both sides are equal will be found. That is the
= 10 kΩ is covered first. Looking at the Input Common
IN
Figure 18
= 22 pF and f
F
.
CM
F
FIGURE 18. Fall Time
= 15 pF. Note that for split supplies V
and
and of course the closest standard value
GBW
Figure 19
F
CM
is 2.7 pF. This moves the pole to
= 88 MHz. Solving for C
chart for C
show the rise and fall times
F
= 10 kΩ and 100 kΩ,
CM
F
must be dealt with.
for the operating
F
30010894
. In trying to
F
the cal-
CM
=
20
In
from the laser. The higher drive levels for the laser gave ring-
ing in the light source as well as light changing from the
thermal characteristics. The hump is due to the thermal char-
acteristics.
Solving for C
lated value is 0.54 pF. One of the problems with more gain is
the very small value for C
measured value being 0.64 pF. For the 0.64 pF location the
pole is at 2.5 MHz.
output.
A transimpedance amplifier is an excellent application for the
LMP7717. Even with the high gain using a 100 kΩ feedback
resistor, the bandwidth is still well over 1 MHz. Other than a
little over compensation for the 10 kΩ feedback resistor con-
figuration using the LMP7717 was quite easy. Of course a
very good board layout was also used for this test.
Figure 18
FIGURE 20. High Gain Response
the ringing and the hump during the on time is
F
using a 100 kΩ feedback resistor, the calcu-
FIGURE 19. Rise Time
Figure 20
F
. A 0.5 pF capacitor was used, its
shows the response for a 1V
30010895
30010896