LMP7711MKE/NOPB National Semiconductor, LMP7711MKE/NOPB Datasheet - Page 16

• Manufacturer Part Number: LMP7711MKE/NOPB
• Description: IC OP AMP PREC 14MHZ LN TSOT23-6
• Manufacturer: National Semiconductor
• Series: LMP®, PowerWise®r

Specifications of LMP7711MKE/NOPB

• Amplifier Type: General Purpose
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• Slew Rate: 11.5 V/µs
• Gain Bandwidth Product: 17MHz
• Current - Input Bias: 0.1pA
• Voltage - Input Offset: 10µV
• Current - Supply: 1.15mA
• Current - Output / Channel: 66mA
• Voltage - Supply, Single/dual (±): 1.8 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: TSOT-23-6, TSOT-6
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Other names: LMP7711MKE

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for current detection. This current needs to be amplified be-
fore it can be further processed. This amplification is per-
formed using a current-to-voltage converter configuration or
transimpedance amplifier. The signal of interest is fed to the
inverting input of an op amp with a feedback resistor in the
current path. The voltage at the output of this amplifier will be
equal to the negative of the input current times the value of
the feedback resistor. Figure 6 shows a transimpedance am-
plifier configuration. C
capacitance and C
tance of the amplifier. The presence of all of these capaci-
tances at higher frequencies might lead to less stable
topologies at higher frequencies. Care must be taken when
designing a transimpedance amplifier to prevent the circuit
from oscillating.
With a wide gain bandwidth product, low input bias current
and low input voltage and current noise, the LMP7711/
LMP7712 are ideal for wideband transimpedance applica-
tions.
A feedback capacitance C
R
sponse. To achieve a maximally flat, 2
and C
Calculating C
pacitor values which are less than 2 pF. This is especially the
case for high speed applications. In these instances, its often
more practical to use the circuit shown in Figure 7 in order to
allow more sensible choices for C
pacitor, C
as R
F
to maintain circuit stability and to control the frequency re-
A
F
<< R
should be chosen by using Equation 3
′
FIGURE 6. Transimpedance Amplifier
F
, is (1+ R
F
.
F
from Equation 3 can sometimes result in ca-
CM
B
/R
D
denotes the common-mode capaci-
A
represents the photodiode parasitic
) C
F
F
is usually added in parallel with
. This relationship holds as long
F
. The new feedback ca-
nd
order response, R
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(3)
F
16
SENSOR INTERFACE
The LMP7711/LMP7712 have low input bias current and low
input referred noise, which make them ideal choices for sen-
sor interfaces such as thermopiles, Infra Red (IR) thermom-
etry, thermocouple amplifiers, and pH electrode buffers.
Thermopiles generate voltage in response to receiving radi-
ation. These voltages are often only a few microvolts. As a
result, the operational amplifier used for this application
needs to have low offset voltage, low input voltage noise, and
low input bias current. Figure 8 shows a thermopile applica-
tion where the sensor detects radiation from a distance and
generates a voltage that is proportional to the intensity of the
radiation. The two resistors, R
vide high gain to amplify this signal, while C
frequency noise.
PRECISION RECTIFIER
Rectifiers are electrical circuits used for converting AC signals
to DC signals. Figure 9 shows a full-wave precision rectifier.
Each operational amplifier used in this circuit has a diode on
its output. This means for the diodes to conduct, the output of
the amplifier needs to be positive with respect to ground. If
V
tom amplifier will be positive. As a result, the diode on the
output of the bottom amplifier will conduct and the signal will
show at the output of the circuit. If V
cycle then the output of the top amplifier will be positive, re-
sulting in the diode on the output of the top amplifier conduct-
ing and, delivering the signal on the amplifier's output to the
circuits output.
For R
equation shown in Figure 9. If R
IN
is in its positive half cycle then only the output of the bot-
FIGURE 7. Modified Transimpedance Amplifier
2
/ R
FIGURE 8. Thermopile Sensor Interface
1
≥
2, the resistor values can be found by using the
A
and R
2
/ R
1
IN
= 1, then R
B
, are selected to pro-
is in its negative half
F
removes the high
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3
should be
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