LMP7731MA/NOPB National Semiconductor, LMP7731MA/NOPB Datasheet - Page 15

• Manufacturer Part Number: LMP7731MA/NOPB
• Description: IC AMP RRIO PREC SGL LN 8SOIC
• Manufacturer: National Semiconductor
• Series: LMP®, PowerWise®r

Specifications of LMP7731MA/NOPB

• Amplifier Type: General Purpose
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• Slew Rate: 2.4 V/µs
• Gain Bandwidth Product: 22MHz
• Current - Input Bias: 14nA
• Voltage - Input Offset: 6µV
• Current - Supply: 2.5mA
• Current - Output / Channel: 49mA
• Voltage - Supply, Single/dual (±): 1.8 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Number Of Channels: 1
• Voltage Gain Db: 130 dB
• Common Mode Rejection Ratio (min): 101 dB
• Input Offset Voltage: 0.5 mV at 5 V
• Operating Supply Voltage: 3 V, 5 V
• Supply Current: 3.4 mA at 5 V
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Lead Free Status / Rohs Status: Details
• Other names: *LMP7731MA/NOPB; LMP7731MA

Measuring the very low peak-to-peak noise performance of
the LMP7731, requires special testing attention. In order to
achieve accurate results, the device should be warmed up for
at least five minutes. This is so that the input offset voltage of
the op amp settles to a value. During this warm up period, the
offset can typically change by a few µV because the chip
temperature increases by about 30°C. If the 10 seconds of
the measurement is selected to include this warm up time,
some of this temperature change might show up as the mea-
sured noise. Figure 4 shows the start-up drift of five typical
LMP7731 units.
FIGURE 3. 0.1 Hz to 10 Hz Input Voltage Noise
FIGURE 4. Start-Up Input Offset Voltage Drift
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During the peak-to-peak noise measurement, the LMP7731
must be shielded. This prevents offset variations due to air-
flow. Offset can vary by a few nV due to this airflow and that
can invalidate measurements of input voltage noise with a
magnitude which is in the same range. For similar reasons,
sudden motions must also be restricted in the vicinity of the
test area. The feed-through which results from this motion
could increase the observed noise value which in turn would
invalidate the measurement.
DIODES BETWEEN THE INPUTS
The LMP7731 has a set of anti-parallel diodes between the
input pins as shown in Figure 5. These diodes are present to
protect the input stage of the amplifier. At the same time, they
limit the amount of differential input voltage that is allowed on
the input pins. A differential signal larger than the voltage
needed to turn on the diodes might cause damage to the
diodes. The differential voltage between the input pins should
be limited to ±3 diode drops or the input current needs to be
limited to ±20 mA.
FIGURE 5. Anti-Parallel Diodes between Inputs
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