Datasheet

 2008-2012 Microchip Technology Inc. DS22092E-page 11
MCP1415/16
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 be minimized. This is
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).
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