Datasheet
MCP1406/07
DS22019B-page 12 2006-2012 Microchip Technology Inc.
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 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.
4.5 Power Dissipation
The total internal power dissipation in a MOSFET driver
is the summation of three separate power dissipation
elements.
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:
4.5.2 QUIESCENT POWER DISSIPATION
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:
4.5.3 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, as described by the
following equation:
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
P
L
fC
T
V
DD
2
=
Where:
f = Switching frequency
C
T
= Total load capacitance
V
DD
= MOSFET driver supply voltage
P
Q
I
QH
DI
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
P
CC
CC f V
DD
=
Where:
CC = Cross-conduction constant (A*sec)
f = Switching frequency
V
DD
= MOSFET driver supply voltage