mic919 Micrel Semiconductor, mic919 Datasheet - Page 6

• Manufacturer Part Number: mic919
• Description: Mic919 27mhz Low-power Sot-23-5/sc-70 Op Amp
• Manufacturer: Micrel Semiconductor

MIC919
Applications Information
The MIC919 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 MIC919 is stable when driving high capacitance, making
it ideal for driving long coaxial cables or other high-capaci-
tance loads.
Phase margin remains constant as load capacitance is
increased. 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 MIC919 is NOT a current feedback device.
Also, for minimum peaking, the feedback resistor should
have low parasitic capacitance, usually 470 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.
MIC919
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 (<100 ) in series with the
output.
6
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
10 F capacitor in parallel with a 0.1 F 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 and SC-70 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 par-
ticular CMRR will reduce.
An MIC919 with no load, dissipates power equal to the
quiescent 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 SOT23-5
package has a thermal resistance of 260 C/W.
Total Power Dissipation P
P
P
Max Allowable Power Dissipation
D
D
(no load)
(output stage)
.
V
V
V
V
V
V
V
I
S
OUT
D
(no load)
I
OUT
T
J
P
(max)
D
October 2001
(outpu stage)
260W
T
t
A
Micrel
(max)