LMP7717MF/NOPB National Semiconductor, LMP7717MF/NOPB Datasheet - Page 19

• 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

Figure 16
amplifier. Only the supply bypass capacitors are not shown.
C
its datasheet. C
the op amp and, for the LMP7717 it is shown in the last graph
of the Typical Performance Characteristics section of this
datasheet. In
is kept at virtual ground. Even though the diode is connected
to the 2.5V line, a power supply line is AC ground, thus C
connected to ground.
Figure 17
back factor, for a transimpedance amplifier. In this figure
C
the diode capacitance and the op amp input capacitance. The
photodiode is close to an ideal current source once its ca-
pacitance is included in the model. What kind of circuit is this?
Without C
resistor. This circuit is a differentiator! Remember, differen-
tiator circuits are inherently unstable and must be compen-
sated. In this case C
Using feedback theory, F = V
divider giving the following equation:
The noise gain is 1/F. Because this is a differentiator circuit,
a zero must be inserted. The location of the zero is given by:
D
D
+ C
represents the photodiode capacitance which is given on
FIGURE 17. Transimpedance Feedback Model
CM
FIGURE 16. Transimpedance Amplifier
= C
shows the schematic needed to derive F, the feed-
F
is the complete schematic for a transimpedance
there is only an input capacitor and a feedback
IN
Figure 16
. Therefore it is critical that the designer knows
CM
is the input common mode capacitance of
F
compensates the circuit.
the inverting input pin of the LMP7717
A
/V
OUT
, this becomes a voltage
30010864
30010861
D
is
19
C
a pole to the circuit. The pole is located at:
To attain maximum bandwidth and still have good stability the
pole is to be located on the open loop gain curve which is A.
If additional compensation is required one can always in-
crease the value of C
of the circuit. Therefore A = 1/F, or AF = 1. For A the equation
is:
The expression f
For a unity gain stable part this is the frequency where A = 1.
For the LMP7717 f
in the following equation:
For the above equation s = jω. To find the actual amplitude of
the equation the square root of the square of the real and
imaginary parts are calculated. At the intersection of F and A,
we have:
F
has been added for stability. The addition of this part adds
GBW
GBW
is the gain bandwidth product of the part.
F
, but this will also reduce the bandwidth
= 88 MHz. Multiplying A and F results
www.national.com