LMH6552MA NSC [National Semiconductor], LMH6552MA Datasheet - Page 16

• Manufacturer Part Number: LMH6552MA
• Description: 1 GHz Fully Differential Amplifier
• Manufacturer: NSC [National Semiconductor]

www.national.com
POWER DISSIPATION
The LMH6552 is optimized for maximum speed and perfor-
mance in the small form factor of the standard SOIC package,
and is essentially a dual channel amplifier. To ensure maxi-
mum output drive and highest performance, thermal shut-
down is not provided. Therefore, it is of utmost importance to
make sure that the T
power dissipation.
Follow these steps to determine the maximum power dissi-
pation for the LMH6552:
1.
2.
3.
FIGURE 11. Single Supply Bypassing Capacitors
Calculate the quiescent (no-load) power: P
(V
through the feedback network if V
Calculate the RMS power dissipated in each of the output
stages: P
− V
and the current measured at the output pins of the
differential amplifier as if they were single ended
amplifiers and V
Calculate the total RMS power: P
FIGURE 10. Split Supply Bypassing Capacitors
S
), where V
−
OUT
) * I
D
(rms) = rms ((V
−
OUT
S
= V
JMAX
) , where V
S
is the total supply voltage.
+
- V
is never exceeded due to the overall
−
. (Be sure to include any current
S
OUT
- V
and I
+
OUT
T
OCM
) * I
= P
OUT
is not mid rail.)
AMP
+
30003501
are the voltage
OUT
30003512
AMP
+ P
) + rms ((V
D
= I
.
CC
*
S
16
The maximum power that the LMH6552 package can dissi-
pate at a given temperature can be derived with the following
equation:
P
(°C) and θ
for a given package (°C/W). For the SOIC package θ
150°C/W.
NOTE: If V
flowing in the feedback network. This current should be in-
cluded in the thermal calculations and added into the quies-
cent power dissipation of the amplifier.
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 perfor-
mance. 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 opera-
tion.
BOARD LAYOUT
The LMH6552 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 a low 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 or 4 mm of the amplifier
as should the supply bypass capacitors. Refer to the section
titled "Power Supply Bypassing" for recommendations on by-
pass circuit layout. Evaluation boards are available free of
charge through the product folder on National’s web site.
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
frequency.
With any differential signal path, symmetry is very important.
Even small amounts of asymmetry can contribute to distortion
and balance errors.
EVALUATION BOARD
National Semiconductor suggests the following evaluation
boards to be used with the LMH6552:
These evaluation boards can be shipped when a device sam-
ple request is placed with National Semiconductor.
Device
LMH6552MA
MAX
= (150° – T
JA
CM
= Thermal resistance, from junction to ambient,
is not 0V then there will be quiescent current
AMB
)/ θ
Package
SOIC
F
JA
and R
, where T
G
for best performance at high
AMB
= Ambient temperature
Evaluation Board
Ordering ID
LMH730154
JA
is