LMH6552_14 Datasheet, PDF (24/32 Pages) Texas Instruments – 1.5 GHz Fully Differential Amplifier

LMH6552
SNOSAX9H – APRIL 2007 – REVISED MARCH 2013
www.ti.com
THERMAL PERFORMANCE
The WSON package is designed for enhanced thermal performance and features an exposed die attach pad
(DAP) at the bottom center of the package that creates a direct path to the PCB for maximum power dissipation.
The DAP is floating and is not electrically connected to internal circuitry. Compared to the traditional leaded
packages where the die attach pad is embedded inside the molding compound, the WSON reduces one layer in
the thermal path.
The thermal advantage of the WSON package is fully realized only when the exposed die attach pad is soldered
down to a thermal land on the PCB board with thermal vias planted underneath the thermal land. The thermal
land can be connected to any power or ground plane within the allowable supply voltage range of the device.
Based on thermal analysis of the WSON package, the junction-to-ambient thermal resistance (θ_JA) can be
improved by a factor of two when the die attach pad of the WSON package is soldered directly onto the PCB
with thermal land and thermal vias are 1.27 mm and 0.33 mm respectively. Typical copper via barrel plating is 1
oz, although thicker copper may be used to further improve thermal performance.
For more information on board layout techniques, refer to Application Note 1187 “Leadless Lead Frame Package
(LLP).” This application note also discusses package handling, solder stencil and the assembly process.
ESD PROTECTION
The LMH6552 is protected against electrostatic discharge (ESD) on all pins. The LMH6552 will survive 2000V
Human Body model and 200V Machine model events. Under normal operation the ESD diodes have no affect on
circuit performance. There are occasions, however, when the ESD diodes will be evident. If the LMH6552 is
driven by a large signal while the device is powered down the ESD diodes will conduct. The current that flows
through the ESD diodes will either exit the chip through the supply pins or will flow through the 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 operation.
BOARD LAYOUT
The LMH6552 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 or 4 mm of the amplifier as
should the supply bypass capacitors. Refer to POWER SUPPLY BYPASSING for recommendations on bypass
circuit layout. Evaluation boards are available free of charge through the product folder on ti.com.
By design, the LMH6552 is relatively insensitive to parasitic capacitance at its inputs. Nonetheless, ground and
power plane metal should be removed from beneath the amplifier and from beneath R_F and R_G for best
performance at high frequency.
With any differential signal path, symmetry is very important. Even small amounts of asymmetry can contribute to
distortion and balance errors.
EVALUATION BOARD
See the LMH6552 Product Folder for evaluation board availability and ordering information.
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