Datasheet

LMP7711
SNOSAP4F –SEPTEMBER 2005–REVISED MAY 2013 www.ti.com
APPLICATION NOTES
LMP7711/LMP7712
The LMP7711/LMP7712 are single and dual, low noise, low offset, rail-to-rail output precision amplifiers with a
wide gain bandwidth product of 17 MHz and low supply current. The wide bandwidth makes the
LMP7711/LMP7712 ideal choices for wide-band amplification in portable applications. The low supply current
along with the enable feature that is built-in on the LMP7711/LMP7712 allows for even more power efficient
designs by turning the device off when not in use.
The LMP7711/LMP7712 are superior for sensor applications. The very low input referred voltage noise of only
5.8 nV/√Hz at 1 kHz and very low input referred current noise of only 10 fA/ √Hz mean more signal fidelity and
higher signal-to-noise ratio.
The LMP7711/LMP7712 have a supply voltage range of 1.8V to 5.5V over a wide temperature range of 0°C to
125°C. This is optimal for low voltage commercial applications. For applications where the ambient temperature
might be less than 0°C, the LMP7711/LMP7712 are fully operational at supply voltages of 2.0V to 5.5V over the
temperature range of −40°C to 125°C.
The outputs of the LMP7711/LMP7712 swing within 25 mV of either rail providing maximum dynamic range in
applications requiring low supply voltage. The input common mode range of the LMP7711/LMP7712 extends to
300 mV below ground. This feature enables users to utilize this device in single supply applications.
The use of a very innovative feedback topology has enhanced the current drive capability of the
LMP7711/LMP7712, resulting in sourcing currents as much as 47 mA with a supply voltage of only 1.8V.
The LMP7711 is offered in the space saving SOT package and the LMP7712 is offered in a 10-pin VSSOP.
These small packages are ideal solutions for applications requiring minimum PC board footprint.
Texas Instruments is heavily committed to precision amplifiers and the market segments they serves. Technical
support and extensive characterization data is available for sensitive applications or applications with a
constrained error budget.
CAPACITIVE LOAD
The unity gain follower is the most sensitive configuration to capacitive loading. The combination of a capacitive
load placed directly on the output of an amplifier along with the output impedance of the amplifier creates a
phase lag which in turn reduces the phase margin of the amplifier. If phase margin is significantly reduced, the
response will be either underdamped or the amplifier will oscillate.
The LMP7711/LMP7712 can directly drive capacitive loads of up to 120 pF without oscillating. To drive heavier
capacitive loads, an isolation resistor, R
ISO
in Figure 54, should be used. This resistor and C
L
form a pole and
hence delay the phase lag or increase the phase margin of the overall system. The larger the value of R
ISO
, the
more stable the output voltage will be. However, larger values of R
ISO
result in reduced output swing and
reduced output current drive.
Figure 54. Isolating Capacitive Load
INPUT CAPACITANCE
CMOS input stages inherently have low input bias current and higher input referred voltage noise. The
LMP7711/LMP7712 enhance this performance by having the low input bias current of only 50 fA, as well as, a
very low input referred voltage noise of 5.8 nV/√Hz. In order to achieve this a larger input stage has been used.
This larger input stage increases the input capacitance of the LMP7711/LMP7712. Figure 55 shows typical input
common mode input capacitance of the LMP7711/LMP7712.
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