Datasheet

© 2007 Microchip Technology Inc. DS22052B-page 11
MCP1401/02
4.5 Power Dissipation
The total internal power dissipation in a MOSFET driver
is the summation of three separate power dissipation
elements.
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 is shown in Equation 4-2.
EQUATION 4-2:
4.5.2 QUIESCENT POWER DISSIPATION
The power dissipation associated with the quiescent
current draw depends upon the state of the input pin.
The MCP1401/02 devices have a quiescent current
draw when the input is high of 0.85 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:
4.5.3 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 described in Equation 4-4.
EQUATION 4-4:
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