mic920 Micrel Semiconductor, mic920 Datasheet - Page 10

• Manufacturer Part Number: mic920
• Description: Mic920 80mhz Low-power Sc-70 Op Amp
• Manufacturer: Micrel Semiconductor

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.
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 follow-
ing 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.
MIC920
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 add-
ing a small resistor (<100Ω) in series with the
output.
10
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 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
par-ticular CMRR will reduce.
An MIC920 with no load, dissipates power equal to the qui-
escent supply current × supply voltage
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.
Ensure the total power dissipated in the device is no greater
than the thermal capacity of the package. The SC70-5 pack-
age has a thermal resistance of 450°C/W.
P
P
Total Power Dissipation = P
Max. Allowable Power Dissipation =
D(no load)
D(output stage)
= V
(
V+
= V
(
– V
V+
V-
– V
)
I
S
OUT
D(no load)
)
I
OUT
T
+ P
J(max)
450°C/W
D(output stage)
March 2006
– T
A(max)