MIC7300 datasheet(12/22 Pages) MICROCHIP

12 / 22 page

MIC7300

DS20006305A-page 12

 2020 Microchip Technology Inc.

determination, one may calculate the maximum

allowable power dissipation and, after subtracting PS,

determine the maximum allowable load current, which

in turn can be used to determine the minimum load

impedance that may safely be driven. The calculation

is summarized below.

EQUATION 4-7:

PDmax



T Jmax



T A

–



--------------------------------

ΘJA(SOT-23-5) = 260°C/W

ΘJA(MSOP-8) = 85°C/W

4.4

Driving Capacitive Loads

Driving a capacitive load introduces phase-lag into the

output signal, and this in turn reduces op-amp system

phase margin. The application that is least forgiving of

reduced phase margin is a unity gain amplifier. The

MIC7300 can typically drive a 2500 pF capacitive load

connected directly to the output when configured as a

unity-gain amplifier and powered with a 2.2V supply. At

10V operation the circuit typically drives 6000 pF.

Phase margin is typically 40 degrees.

4.5

Using Large-Value Feedback

Resistors

A large-value feedback resistor (> 500 kΩ) can reduce

the phase margin of a system. This occurs when the

feedback resistor acts in conjunction with input

capacitance to create phase lag in the feedback signal.

Input capacitance is usually a combination of input

circuit components and other parasitic capacitance,

such as amplifier input capacitance and stray printed

circuit board capacitance.

Figure 4-2 illustrates a method of compensating phase

lag caused by using a large-value feedback resistor.

Feedback capacitor CFB introduces sufficient phase

lead to overcome the phase lag caused by feedback

resistor RFB and input capacitance CIN. The value of

CFB is determined by first estimating CIN and then

applying the following formula shown in Equation 4-8:

EQUATION 4-8:

RIN CIN



RFB





VIN

CFB

RFB

VOUT

CIN

RIN

FIGURE 4-2:

Canceling Feedback Phase

Lag.

Because a significant percentage of CIN may be

caused by board layout, it is important to note that the

correct value of CFB may change when changing from

a breadboard to the final circuit layout.

4.6

Typical Circuits

Some single-supply, rail-to-rail applications for which

the MIC7300 is well suited are shown in the circuit

diagrams of Figure 4-3 through Figure 4-8.

910k

100k

VOUT

0V to V+

V+

2.2V to 10V

VIN

MIC7300

0V to

V+

FIGURE 4-3:

Non-Inverting Amplifier.

VIN (V)

V+

V =+

FIGURE 4-4:

Non-Inverting Amplifier

Behavior.

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