Datasheet

LMP7701, LMP7702, LMP7704
SNOSAI9H –SEPTEMBER 2005–REVISED MARCH 2013 www.ti.com
APPLICATION INFORMATION
LMP7701/LMP7702/LMP7704
The LMP7701/LMP7702/LMP7704 are single, dual, and quad low offset voltage, rail-to-rail input and output
precision amplifiers each with a CMOS input stage and wide supply voltage range of 2.7V to 12V. The
LMP7701/LMP7702/LMP7704 have a very low input bias current of only ±200 fA at room temperature.
The wide supply voltage range of 2.7V to 12V over the extensive temperature range of −40°C to 125°C makes
the LMP7701/LMP7702/LMP7704 excellent choices for low voltage precision applications with extensive
temperature requirements.
The LMP7701/LMP7702/LMP7704 have only ±37 μV of typical input referred offset voltage and this offset is
specified to be less than ±500 μV for the single and ±520 μV for the dual and quad, over temperature. This
minimal offset voltage allows more accurate signal detection and amplification in precision applications.
The low input bias current of only ±200 fA along with the low input referred voltage noise of 9 nV/√Hz gives the
LMP7701/LMP7702/LMP7704 superiority for use in sensor applications. Lower levels of noise from the
LMP7701/LMP7702/LMP7704 mean of better signal fidelity and a higher signal-to-noise ratio.
Texas Instruments is heavily committed to precision amplifiers and the market segment they serve. Technical
support and extensive characterization data is available for sensitive applications or applications with a
constrained error budget.
The LMP7701 is offered in the space saving 5-Pin SOT-23 and 8-Pin SOIC package. The LMP7702 comes in
the 8-Pin SOIC and 8-Pin VSSOP package. The LMP7704 is offered in the 14-Pin SOIC and 14-Pin TSSOP
package. These small packages are ideal solutions for area constrained PC boards and portable electronics.
CAPACITIVE LOAD
The LMP7701/LMP7702/LMP7704 can each be connected as a non-inverting unity gain follower. This
configuration is the most sensitive to capacitive loading.
The combination of a capacitive load placed on the output of an amplifier along with the amplifier's output
impedance creates a phase lag which in turn reduces the phase margin of the amplifier. If the phase margin is
significantly reduced, the response will be either underdamped or it will oscillate.
In order to drive heavier capacitive loads, an isolation resistor, R
ISO
, in Figure 45 should be used. By using this
isolation resistor, the capacitive load is isolated from the amplifier's output, and hence, the pole caused by C
L
is
no longer in the feedback loop. The larger the value of R
ISO
, the more stable the output voltage will be. If values
of R
ISO
are sufficiently large, the feedback loop will be stable, independent of the value of C
L
. However, larger
values of R
ISO
result in reduced output swing and reduced output current drive.
Figure 45. Isolating Capacitive Load
INPUT CAPACITANCE
CMOS input stages inherently have low input bias current and higher input referred voltage noise. The
LMP7701/LMP7702/LMP7704 enhance this performance by having the low input bias current of only ±200 fA, as
well as, a very low input referred voltage noise of 9 nV/√Hz. In order to achieve this a larger input stage has been
used. This larger input stage increases the input capacitance of the LMP7701/LMP7702/ LMP7704. The typical
value of this input capacitance, C
IN
, for the LMP7701/LMP7702/LMP7704 is 25 pF. The input capacitance will
interact with other impedances such as gain and feedback resistors, which are seen on the inputs of the
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