LMH6551Q Datasheet, PDF (17/20 Pages) Texas Instruments – Differential, High Speed Op Amp

device, hence it is possible to power up a chip with a large
signal applied to the input pins. Using the shutdown mode is
one way to conserve power and still prevent unexpected op-
eration.
BOARD LAYOUT
The LMH6551Q is a very high performance amplifier. In order
to get maximum benefit from the differential circuit architec-
ture board layout and component selection is very critical. The
circuit board should have low a inductance ground plane and
well bypassed broad supply lines. External components
should be leadless surface mount types. The feedback net-
work and output matching resistors should be composed of
short traces and precision resistors (0.1%). The output match-
ing resistors should be placed within 3-4 mm of the amplifier
as should the supply bypass capacitors. The LMH730154
evaluation board is an example of good layout techniques.
The LMH6551Q is sensitive to parasitic capacitances on the
amplifier inputs and to a lesser extent on the outputs as well.
Ground and power plane metal should be removed from be-
neath the amplifier and from beneath R_F and R_G.
With any differential signal path symmetry is very important.
Even small amounts of asymmetry will contribute to distortion
and balance errors.
EVALUATION BOARD
National Semiconductor offers evaluation board(s) to aid in
device testing and characterization and as a guide for proper
layout. Generally, a good high frequency layout will keep
power supply and ground traces away from the inverting input
and output pins. Parasitic capacitances on these nodes to
ground will cause frequency response peaking and possible
circuit oscillations (see Application Note OA-15 for more in-
formation).
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