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MCP1406/07
4.4
PCB Layout Considerations
4.5.2
QUIESCENT POWER DISSIPATION
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 induc-
tance 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 V DD ,
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.
The power dissipation associated with the quiescent
current draw depends upon 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 dissipation is:
P Q = ? I QH ? D + I QL ? ? 1 – D ? ? ? V DD
Where:
I QH = Quiescent current in the high state
D = Duty cycle
I QL = Quiescent current in the low state
V DD = MOSFET driver supply voltage
4.5
Power Dissipation
4.5.3 OPERATING POWER DISSIPATION
The operating power dissipation occurs each time the
The total internal power dissipation in a MOSFET driver
is the summation of three separate power dissipation
elements.
P T = P L + P Q + P CC
Where:
P T = Total power dissipation
P L = Load power dissipation
P Q = Quiescent power dissipation
P CC = Operating power dissipation
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, as described by the
following equation:
P CC = CC ? f ? V DD
Where:
CC = Cross-conduction constant (A*sec)
f = Switching frequency
V DD = MOSFET driver supply voltage
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 is:
P L = f ? C T ? V DD
2
Where:
f = Switching frequency
C T = Total load capacitance
V DD = MOSFET driver supply voltage
DS22019B-page 12
? 2006-2012 Microchip Technology Inc.