MCP1415RT datasheet(12/20 Pages) MICROCHIP

12 / 20 page

MCP1415/16

DS22092C-page 12

4.4

Power Dissipation

The total internal power dissipation in a MOSFET driver

is the summation of three separate power dissipation

elements.

EQUATION 4-1:

4.4.1

CAPACITIVE LOAD DISSIPATION

The power dissipation caused by a capacitive load is a

direct function of the frequency, total capacitive load,

and supply voltage. The power lost in the MOSFET

driver for a complete charging and discharging cycle of

a MOSFET is shown in Equation 4-2.

EQUATION 4-2:

4.4.2

QUIESCENT POWER DISSIPATION

The power dissipation associated with the quiescent

current draw depends upon the state of the input pin.

The MCP1415/16 devices have a quiescent current

draw when the input is high of 0.65 mA (typical) and

0.1 mA (typical) when the input is low. The quiescent

power dissipation is shown in Equation 4-3.

EQUATION 4-3:

4.4.3

OPERATING POWER DISSIPATION

The operating power dissipation occurs each time the

MOSFET driver output transitions because for a very

short period of time both MOSFETs in the output stage

are on simultaneously. This cross-conduction current

leads to a power dissipation describe in Equation 4-4.

EQUATION 4-4:

4.5

PCB Layout Considerations

Proper PCB layout is important in high current, fast

switching circuits to provide proper device operation

and robustness of design. Improper component

placement may cause errant switching, excessive

voltage ringing, or circuit latch-up. PCB trace loop area

and

inductance

must

minimized.

This

accomplished by placing the MOSFET driver directly at

the load and placing the bypass capacitor directly at the

MOSFET driver (Figure 4-3). Locating ground planes

or ground return traces directly beneath the driver

output signal also reduces trace inductance. A ground

plane will also help as a radiated noise shield as well as

providing some heat sinking for power dissipated within

the device (Figure 4-4).

FIGURE 4-3:

Recommended PCB Layout

(TOP).

FIGURE 4-4:

Recommended PCB Layout

(BOTTOM).

Where:

Total power dissipation

Load power dissipation

Quiescent power dissipation

PCC

Operating power dissipation

Where:

Switching frequency

Total load capacitance

VDD

MOSFET driver supply voltage

–

()

() V

Where:

IQH

Quiescent current in the high

state

Duty cycle

IQL

Quiescent current in the low

state

VDD

MOSFET driver supply voltage

Where:

Cross-conduction constant

(A*sec)

Switching frequency

VDD

MOSFET driver supply voltage

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