Micrel, Inc.

MIC910

Application Information

The

MIC910

is

a

high-speed,

voltage-feedback

operational amplifier featuring very low supply current

and excellent stability. This device is unity gain stable

and capable of driving high capacitance loads.

Driving High Capacitance

The MIC910 is stable when driving any capacitance (see

the “Gain Bandwidth and Phase Margin vs. Load

Capacitance”

graph

in

the

Typical

Characteristics

section) 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 the “Gain Bandwidth and Phase

Margin vs. Load” in the Typical Characteristics section).

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

Ω) in series with the output.

Feedback Resistor Selection

Conventional op amp gain configurations and resistor

selection apply; the MIC910 is not a current feedback

device. Resistor values in the range of 1k

Ω to 10kΩ are

recommended.

Layout Considerations

All high-speed devices require careful PCB layout. The

high stability and high PSRR of the MIC910 make it

easier to use than most other op amps, but the following

guidelines should be observed:

• Capacitance, particularly 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

capacitors 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 is ideal. For best

performance, all bypassing capacitors should be located

as close to the op amp as possible and all capacitors

should be low equivalent series inductance (ESL) and

equivalent

series

resistance

(ESR).

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.

A MIC910 with no load, dissipates power equal to the

quiescent supply current × the supply voltage (Equation

1):

Eq. 1

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 (Equation 2).

Eq. 2

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

(Equation 3).

Maximum Allowable Power Dissipation =

W

/

C

260

T

T

)

MAX

(

A

)

MAX

(

J

°

−

Eq. 3

September 19, 2014

12

Revision 2.0