MCP1407-ESLASHP datasheet(13/30 Pages) MICROCHIP

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DS20002019C-page 13

MCP1406/07

4.4

PCB Layout Considerations

Proper PCB layout is important in a high current,

fast switching circuit to provide proper device operation

and robustness of design. PCB trace loop area and

inductance should be minimized by the use of a ground

plane or ground trace located under the MOSFET gate

drive signals, separate analog and power grounds, and

local driver decoupling.

The MCP1406/07 devices have two pins each for VDD,

OUTPUT and GND. Both pins must be used for proper

operation. This also lowers path inductance which will,

along with proper decoupling, help minimize ringing in

the circuit.

Placing a ground plane beneath the MCP1406/07 will

help as a radiated noise shield as well as providing

some heat sinking for power dissipated within the

device.

4.5

Power Dissipation

The total internal power dissipation in a MOSFET driver

is the summation of three separate power dissipation

elements, which can be calculated by using the

following equation:

EQUATION 4-1:

4.5.1

CAPACITIVE LOAD DISSIPATION

The power dissipation caused by a capacitive load is a

direct function of frequency, total capacitive load and

supply voltage. The power lost in the MOSFET driver

for a complete charging and discharging cycle of a

MOSFET can be determined by means of this

equation:

EQUATION 4-2:

4.5.2

QUIESCENT POWER DISSIPATION

The power dissipation associated with the quiescent

current draw depends on the state of the input pin. The

MCP1406/07 devices have a quiescent current draw

when the input is high of 0.13 mA (typ) and 0.035 mA

(typ) when the input is low. The quiescent power dissi-

pation can be determined by using this equation:

EQUATION 4-3:

4.5.3

OPERATING POWER DISSIPATION

The operating power dissipation occurs each time the

MOSFET driver output transitions; this is 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, as described by

the following equation:

EQUATION 4-4:

PL PQ PCC

Where:

PT = Total power dissipation

PL = Load power dissipation

PQ = Quiescent power dissipation

PCC = Operating power dissipation

fCT VDD



Where:

f = Switching frequency

CT = Total load capacitance

VDD = MOSFET driver supply voltage

IQH DIQL

1 D

–





 V



Where:

IQH = Quiescent current in the high state

D = Duty cycle

IQL = Quiescent current in the low state

VDD = MOSFET driver supply voltage

PCC

CC f



VDD



Where:

CC = Cross-conduction constant (A sec.)

f = Switching frequency

VDD = MOSFET driver supply voltage

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