LM7171AMJ-QML National Semiconductor, LM7171AMJ-QML Datasheet - Page 14

• Manufacturer Part Number: LM7171AMJ-QML
• Description: Very High Speed/ High Output Current/ Voltage Feedback Amplifier
• Manufacturer: National Semiconductor

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Termination
To minimize reflection, coaxial cable with matching charac-
teristic impedance to the signal source should be used. The
other end of the cable should be terminated with the same
value terminator or resistor. For the commonly used cables,
RG59 has 75
50
Driving Capacitive Loads
Amplifiers driving capacitive loads can oscillate or have ring-
ing at the output. To eliminate oscillation or reduce ringing,
an isolation resistor can be placed as shown below in Figure
5 The combination of the isolation resistor and the load ca-
pacitor forms a pole to increase stability by adding more
phase margin to the overall system. The desired perfor-
mance depends on the value of the isolation resistor; the big-
ger the isolation resistor, the more damped the pulse re-
sponse becomes. For LM7171, a 50
recommended for initial evaluation. Figure 6 shows the
LM7171 driving a 150 pF load with the 50 isolation resistor.
characteristic impedance.
FIGURE 4. Improperly Terminated Signal
FIGURE 3. Properly Terminated Signal
characteristic impedance, and RG58 has
(Continued)
isolation resistor is
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14
Power Dissipation
The maximum power allowed to dissipate in a device is de-
fined as:
Where
For example, for the LM7171 in a SO-8 package, the maxi-
mum power dissipation at 25˚C ambient temperature is
730 mW.
Thermal resistance,
die size, package size and package material. The smaller
the die size and package, the higher
DIP package has a lower thermal resistance (108˚C/W) than
that of 8-pin SO (172˚C/W). Therefore, for higher dissipation
capability, use an 8-pin DIP package.
The total power dissipated in a device can be calculated as:
P
connected at the output. P
vice with a load connected at the output; it is not the power
dissipated by the load.
Furthermore,
Q
PD
T
T
P
P
JA
is the quiescent power dissipated in a device with no load
J(max)
A
Q
L
:
FIGURE 6. The LM7171 Driving a 150 pF Load
:
=
=
FIGURE 5. Isolation Resistor Used
supply current x total supply voltage with no load
output current x (voltage difference between
supply voltage and output voltage of the same
side of supply voltage)
is the power dissipation in a device
is the maximum junction temperature
is the ambient temperature
is the thermal resistance of a particular package
with a 50
to Drive Capacitive Load
P
D
= (T
JA
P
, depends on parameters such as
D
L
J(max)
Isolation Resistor
= P
is the power dissipated in the de-
Q
− T
+ P
A
L
)/
JA
JA
becomes. The 8-pin
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