MIC4451YN datasheet(11/24 Pages) MICROCHIP

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

2021 Microchip Technology Inc. and its subsidiaries

DS20006616A-page 11

MIC4451/52

FIGURE 4-1:

Switching Time Degradation

Due to Negative Feedback.

The supply current vs. frequency and supply current vs

capacitive load characteristic curves aid in determining

power dissipation calculations. Table 4-1 lists the

maximum safe operating frequency for several power

supply voltages when driving a 10,000 pF load. More

accurate power dissipation figures can be obtained by

summing the three dissipation sources.

Given the power dissipation in the device and the

thermal resistance of the package, junction operating

temperature for any ambient is easy to calculate. For

example, the thermal resistance of the 8-lead plastic

DIP package, from the data sheet, is 130°C/W. In a

25°C ambient, then, using a maximum junction

temperature of 125°C, this package will dissipate

960 mW.

Accurate power dissipation numbers can be obtained

by summing the three sources of power dissipation in

the device:

• Load Power Dissipation (PL)

• Quiescent power dissipation (PQ)

• Transition power dissipation (PT)

Calculation of load power dissipation differs depending

on whether the load is capacitive, resistive or inductive.

4.5

Resistive Load Power Dissipation

Dissipation caused by a resistive load can be

calculated as:

EQUATION 4-1:

4.6

Capacitive Load Power

Dissipation

Dissipation caused by a capacitive load is simply the

energy placed in, or removed from, the load

capacitance by the driver. The energy stored in a

capacitor is described by the equation:

EQUATION 4-2:

Because this energy is lost in the driver each time the

load is charged or discharged, the “1/2” is removed for

power dissipation calculations. This equation also

shows that it is good practice not to place more voltage

on the capacitor than is necessary, as dissipation

increases as the square of the voltage applied to the

capacitor. For a driver with a capacitive load:

EQUATION 4-3:

4.7

Inductive Load Power Dissipation

For inductive loads, the situation is more complicated.

For the part of the cycle in which the driver is actively

forcing current into the inductor, the situation is the

same as it is in the resistive case:

EQUATION 4-4:

PL I

2 R



Where:

I = The current drawn by the load.

RO = The output resistance of the driver when the

output is high, at the power supply voltage used.

D = The fraction of time the load is conducting (duty

cycle).

TABLE 4-1:

MIC4451 MAX. OPERATION

FREQUENCY

Max. Frequency

18V

220 kHz

15V

300 kHz

10V

640 kHz

2 MHz

--- C



PL f C



 2



Where:

f = Operating frequency.

C = Load capacitance.

VS = Driver supply voltage.

PL1 I

2 R



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