Datasheet

+
-
V
OUT
V
IN
R
ISO
C
L
R
1
R
2
LMP7707, LMP7708, LMP7709
SNOSAW5B –JUNE 2007–REVISED MARCH 2013 www.ti.com
APPLICATION INFORMATION
LMP7707/LMP7708/LMP7709
The LMP7707/LMP7708/LMP7709 devices are single, dual and quad low offset voltage, rail-to-rail input and
output precision amplifiers each with a CMOS input stage and the wide supply voltage range of 2.7V to 12V. The
LMP7707/LMP7708/LMP7709 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
either the LMP7707, LMP7708 or LMP7709 an excellent choice for low voltage precision applications with
extensive temperature requirements.
The LMP7707/LMP7708/LMP7709 have only ±37 µV of typical input referred offset voltage and this offset is
ensured 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 give the
LMP7707/LMP7708/LMP7709 superior qualities for use in sensor applications. Lower levels of noise introduced
by the amplifier mean better signal fidelity and a higher signal-to-noise ratio.
The LMP7707/LMP7708/LMP7709 are stable for a gain of 6 or higher. With proper compensation though, the
LMP7707, LMP7708 or LMP7709 can be operational at a gain of ±1 and still maintain much faster slew rates
than comparable fully compensated amplifiers. The increase in bandwidth and slew rate is obtained without any
additional power consumption.
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 LMP7707 is offered in the space-saving 5-pin SOT-23 and 8-pin SOIC packages, the LMP7708 comes in the
8-pin VSSOP and 8-pin SOIC packages, and the LMP7709 is offered in the 14-pin TSSOP and 14-pin SOIC
packages. These small packages are ideal solutions for area constrained PC boards and portable electronics.
CAPACITIVE LOAD
The LMP7707/LMP7708/LMP7709 devices can each be connected as a non-inverting voltage 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
, as shown in the circuit 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
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Product Folder Links: LMP7707 LMP7708 LMP7709