Datasheet

LMP7715, LMP7716, LMP7716Q
SNOSAV0E –MARCH 2006–REVISED MARCH 2013 www.ti.com
APPLICATION INFORMATION
LMP7715/LMP7716/LMP7716Q
The LMP7715/LMP7716/LMP7716Q 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
LMP7715/LMP7716/LMP7716Q ideal choices for wide-band amplification in portable applications.
The LMP7715/LMP7716/LMP7716Q 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 LMP7715/LMP7716/LMP7716Q 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 LMP7715/LMP7716/LMP7716Q 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 LMP7715/LMP7716/LMP7716Q swing within 25 mV of either rail providing maximum dynamic
range in applications requiring low supply voltage. The input common mode range of the
LMP7715/LMP7716/LMP7716Q 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
LMP7715/LMP7716/LMP7716Q, resulting in sourcing currents of as much as 47 mA with a supply voltage of only
1.8V.
The LMP7715 is offered in the space saving SOT-23 package and the LMP7716/LMP7716Q is offered in an 8-
pin VSSOP. These small packages are ideal solutions for applications requiring minimum PC board footprint.
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 LMP7715/LMP7716/LMP7716Q can directly drive capacitive loads of up to 120 pF without oscillating. To
drive heavier capacitive loads, an isolation resistor, R
ISO
as shown in Figure 49, 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 49. Isolating Capacitive Load
INPUT CAPACITANCE
CMOS input stages inherently have low input bias current and higher input referred voltage noise. The
LMP7715/LMP7716/LMP7716Q 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 LMP7715/LMP7716/LMP7716Q.
Figure 50 shows typical input common mode capacitance of the LMP7715/LMP7716/LMP7716Q.
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