Datasheet

LMH6553
www.ti.com SNOSB07H –SEPTEMBER 2008–REVISED MARCH 2013
The maximum power that the LMH6553 package can dissipate at a given temperature can be derived with the
following equation:
P
MAX
= (150° – T
AMB
)/ θ
JA
where
• T
AMB
= Ambient temperature (°C)
• θ
JA
= Thermal resistance, from junction to ambient, for a given package (°C/W)
• For the SO PowerPAD package θ
JA
is 59°C/W
• For WSON package θ
JA
is 58°C/W (4)
Note: If V
CM
is not mid-rail, then there will be quiescent current flowing in the feedback network. This current
should be included in the thermal calculations and added into the quiescent power dissipation of the amplifier.
THERMAL PERFORMANCE
The LMH6553 is available in both the SO PowerPAD and WSON packages. Both packages are 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.
The thermal advantage of the two packages 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.
The junction-to-ambient thermal resistance (θ
JA
) of the LMH6553 can be significantly lowered, as opposed to an
alternative with no direct soldering to a thermal land. 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 for the WSON package, refer to Application Note 1187
(literature number SNOA401). This application note also discusses package handling, solder stencil and the
assembly process.
ESD PROTECTION
The LMH6553 is protected against electrostatic discharge (ESD) on all pins. The LMH6553 will survive 4000V
Human Body model and 350V Machine model events. Under normal operation the ESD diodes have no effect on
circuit performance. The current that flows through the ESD diodes will either exit the chip through the supply
pins or through the device, hence it is possible to power up a chip with a large signal applied to the input pins.
BOARD LAYOUT
The LMH6553 is a very high performance amplifier. In order to get maximum benefit from the differential circuit
architecture, board layout and component selection are very critical. The circuit board should have a low
inductance ground plane and well bypassed wide 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’s web site.
By design, the LMH6553 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 LMH6553 Product Folder for evaluation board availability and ordering information.
Copyright © 2008–2013, Texas Instruments Incorporated Submit Documentation Feedback 29
Product Folder Links: LMH6553