MIC914(2000) 데이터 시트보기 (PDF) - Micrel
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MIC914 Datasheet PDF : 12 Pages
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MIC914
Applications Information
The MIC914 is a high-speed, voltage-feedback operational
amplifier featuring very low supply current and excellent
stability. This device is unity gain stable with RL ≤ 200Ω and
capable of driving high capacitance loads.
Stability Considerations
The MIC914 is unity gain stable and it is capable of driving
unlimited capacitance loads, but some design considerations
are required to ensure stability. The output needs to be
loaded with 200Ω resistance or less and/or have suffi-
cient load capacitance to achieve stability (refer to the
“Load Capacitance vs. Phase Margin” graph).
For applications requiring a little less speed, Micrel offers the
MIC911, a more heavily compensated version of the MIC914
which provides extremely stable operation for all load resis-
tance and capacitance.
For stability considerations at different supply voltages, please
refer to the graph elsewhere in the datasheet entitled "Gain
Bandwidth and Phase Margin vs. Supply Voltage".
Driving High Capacitance
The MIC914 is stable when driving high capacitance (see
“Typical Characteristics: Gain Bandwidth and Phase Margin
vs. Load Capacitance”) making it ideal for driving long coaxial
cables or other high-capacitance loads.
Phase margin remains constant as load capacitance is
increased. Most high-speed op amps are only able to drive
limited capacitance.
Note: increasing load capacitance does reduce the
speed of the device (see “Typical Characteris-
tics: Gain Bandwidth and Phase Margin vs.
Load”). In applications where the load capaci-
tance reduces the speed of the op amp to an
unacceptable level, the effect of the load capaci-
tance 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 MIC914 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.
Micrel
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.
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 SOT-23-5 package, like all small packages, has a high
thermal resistance. It is important 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 particular CMRR will reduce.
An MIC914 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 SOT23-5
package has a thermal resistance of 260°C/W.
Max. Allowable Power Dissipation = TJ(max) −TA(max)
260W
MIC914
10
June 2000
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