LMH6551 Datasheet, PDF (22/32 Pages) National Semiconductor (TI) – Differential, High Speed Op Amp

LMH6551
SNOSAK7D – FEBRUARY 2005 – REVISED JANUARY 2015
11 Layout
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11.1 Layout Guidelines
The LMH6551 is a very high performance amplifier. In order to get maximum benefit from the differential circuit
architecture, board layout and component selection is very critical. The circuit board should have a low
inductance ground plane and well bypassed broad supply lines. External components should be leadless surface
mount types. The feedback network and output matching resistors should be composed of short traces and
precision resistors (0.1%). The output matching 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 LMH6551 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 beneath 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.
Texas Instruments 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.
11.2 Layout Example
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Figure 36. Layout Schematic
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