Datasheet MIC920 (Micrel) - 10

MIC920 Micrel, Inc.
Applications Information Power Supply Bypassing
The MIC920 is a high-speed, voltage-feedback operational Regular supply bypassing techniques are recommended. amplifier featuring very low supply current and excellent A 10µF capacitor in parallel with a 0.1µF capacitor on both stability. This device is unity gain stable, capable of driving the positive and negative supplies are ideal. For best perfor- high capacitance loads. mance all bypassing capacitors should be located as close
Driving High Capacitance
to the op amp as possible and all capacitors should be low ESL (equivalent series inductance), ESR (equivalent series The MIC920 is stable when driving high capacitance, making resis-tance). Surface-mount ceramic capacitors are ideal. it ideal for driving long coaxial cables or other high-capaci- tance loads. Most high-speed op amps are only able to drive
Thermal Considerations
limited capacitance. The SC70-5 package and the SOT-23-5 package, like all Note: increasing load capacitance does reduce smal packages, have a high thermal resistance. It is important the speed of the device. In applications where to ensure the IC does not exceed the maximum operating the load capacitance reduces the speed of the junction (die) temperature of 85°C. The part can be operated op amp to an unacceptable level, the effect of up to the absolute maximum temperature rating of 125°C, the load capacitance can be reduced by add- but between 85°C and 125°C performance will degrade, in ing a small resistor (<100Ω) in series with the par-ticular CMRR will reduce. output. An MIC920 with no load, dissipates power equal to the qui-
Feedback Resistor Selection
escent supply current × supply voltage Conventional op amp gain configurations and resistor selec- PD(no load) = VV+ – VV- I ( ) S tion apply, the MIC920 is NOT a current feedback device. Also, for minimum peaking, the feedback resistor should have When a load is added, the additional power is dissipated in low parasitic capacitance, usually 470Ω is ideal. To use the the output stage of the op amp. The power dissipated in the part as a follower, the output should be connected to input device is a function of supply voltage, output voltage and via a short wire. output current.
Layout Considerations
PD(output stage) = VV+ – VOUT I ( ) OUT All high speed devices require careful PCB layout. The follow- ing guidelines should be observed: Capacitance, par-ticularly Total Power Dissipation = PD(no load) + PD(output stage) on the two inputs pins will degrade performance; avoid large copper traces to the inputs. Keep the output signal away from Ensure the total power dissipated in the device is no greater the inputs and use a ground plane. than the thermal capacity of the package. The SC70-5 pack- age has a thermal resistance of 450°C/W. It is important to ensure adequate supply bypassing capaci- T tors are located close to the device. Max. Allowable Power Dissipation = J(max) – TA(max) 450°C/W MIC920 10 March 2006