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MIC920 Datasheet, PDF (10/11 Pages) Micrel Semiconductor – 80MHz Low-Power SC-70 Op Amp
MIC920
Applications Information
The MIC920 is a high-speed, voltage-feedback operational
amplifier featuring very low supply current and excellent
stability. This device is unity gain stable, capable of driving
high capacitance loads.
Driving High Capacitance
The MIC920 is stable when driving high capacitance, making
it ideal for driving long coaxial cables or other high-capaci-
tance loads. Most high-speed op amps are only able to drive
limited capacitance.
Note: increasing load capacitance does reduce
the speed of the device. In applications where
the load capacitance reduces the speed of the
op amp to an unacceptable level, the effect of
the load capacitance can be reduced by adding
a small resistor (<100Ω) in series with the
output.
Feedback Resistor Selection
Conventional op amp gain configurations and resistor selec-
tion apply, the MIC920 is NOT a current feedback device.
Also, for minimum peaking, the feedback resistor should
have low parasitic capacitance, usually 470Ω is ideal. To use
the part as a follower, the output should be connected to input
via a short wire.
Layout Considerations
All high speed devices require careful PCB layout. The
following guidelines should be observed: Capacitance, par-
ticularly on the two inputs pins will degrade performance;
avoid large copper traces to the inputs. Keep the output signal
away from the inputs and use a ground plane.
It is important to ensure adequate supply bypassing capaci-
tors are located close to the device.
Micrel
Power Supply Bypassing
Regular supply bypassing techniques are recommended. A
10µF capacitor in parallel with a 0.1µF capacitor on both the
positive and negative supplies are ideal. For best perfor-
mance all bypassing capacitors should be located as close to
the op amp as possible and all capacitors should be low ESL
(equivalent series inductance), ESR (equivalent series resis-
tance). Surface-mount ceramic capacitors are ideal.
Thermal Considerations
The SC70-5 package and the SOT-23-5 package, like all
small packages, have a high thermal resistance. It is impor-
tant to ensure the IC does not exceed the maximum operating
junction (die) temperature of 85°C. The part can be operated
up to the absolute maximum temperature rating of 125°C, but
between 85°C and 125°C performance will degrade, in par-
ticular CMRR will reduce.
An MIC920 with no load, dissipates power equal to the
quiescent supply current × supply voltage
( ) PD(no load) = VV + −VV − IS
When a load is added, the additional power is dissipated in
the output stage of the op amp. The power dissipated in the
device is a function of supply voltage, output voltage and
output current.
( ) PD(output stage) = VV + −VOUT IOUT
Total Power Dissipation = PD(no load) + PD(output stage)
Ensure the total power dissipated in the device is no greater
than the thermal capacity of the package. The SC70-5
package has a thermal resistance of 450°C/W.
Max. AllowablePowerDissipation = TJ(max) − TA(max)
450°C / W
MIC920
10
December 2001