lmh6550mm National Semiconductor Corporation, lmh6550mm Datasheet - Page 14

• Manufacturer Part Number: lmh6550mm
• Description: Differential, High Speed Op Amp
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Section
FIGURE 10. Calculating Transformer Circuit Net Gain
FIGURE 11. Transformer Out Low Impedance Load
FIGURE 9. Transformer Out High Impedance Load
(Continued)
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14
CAPACITIVE DRIVE
As noted in the Driving ADC section, capacitive loads should
be isolated from the amplifier output with small valued resis-
tors. This is particularly the case when the load has a resis-
tive component that is 500Ω or higher. A typical ADC has
capacitive components of around 10 pF and the resistive
component could be 1000Ω or higher. If driving a transmis-
sion line, such as 50Ω coaxial or 100Ω twisted pair, using
matching resistors will be sufficient to isolate any subse-
quent capacitance. For other applications see the “Sug-
gested R
mance Characteristics section.
POWER DISSIPATION
The LMH6550 is optimized for maximum speed and perfor-
mance in the small form factor of the standard SOIC pack-
age, and is essentially a dual channel amplifier. To ensure
maximum output drive and highest performance, thermal
shutdown is not provided. Therefore, it is of utmost impor-
tance to make sure that the T
the overall power dissipation.
Follow these steps to determine the Maximum power dissi-
pation for the LMH6550:
1. Calculate the quiescent (no-load) power: P
2. Calculate the RMS power dissipated in each of the
3. Calculate the total RMS power: P
The maximum power that the LMH6550 package can dissi-
pate at a given temperature can be derived with the following
equation:
P
ture (˚C) and θ
ambient, for a given package (˚C/W). For the SOIC package
θ
JA
MAX
(V
through the feedback network if V
output stages: P
rms ((V
the voltage and the current measured at the output pins
of the differential amplifier as if they were single ended
amplifiers and V
is 150˚C/W, and for the MSOP package it is 235˚C/W.
= (150˚ – T
S
), where V
FIGURE 12. Driving 50Ω Test Equipment
OUT
S
− V
vs. Cap Load” charts in the Typical Perfor-
JA
AMB
−
S
OUT
= V
= Thermal resistance, from junction to
S
D
)/ θ
) * I
is the total supply voltage.
+
(rms) = rms ((V
JA
- V
−
, where T
OUT
−
. (Be sure to include any current
JMAX
) , where V
is never exceeded due to
AMB
T
OCM
S
= P
= Ambient tempera-
- V
OUT
is not mid rail.)
AMP
+
OUT
and I
+ P
) * I
AMP
20130103
D
OUT
+
.
OUT
= I
CC
are
) +
*