Datasheet

MCP14700
DS22201B-page 14  2009-2013 Microchip Technology Inc.
5.4 PCB Layout
Proper PCB layout is important in a high current, fast
switching circuit to provide proper device operation.
Improper component placement may cause errant
switching, excessive voltage ringing, or circuit latch-up.
There are two important states of the MCP14700
outputs, high and low. Figure 5-1 depicts the current
flow paths when the outputs of the MCP14700 are high
and the power MOSFETs are turned on. The charge
needed to turn on the low-side power MOSFET comes
from the decoupling capacitor C
VCC
. The current flows
from this capacitor through the internal LOWDR
circuitry, into the gate of the low-side power MOSFET,
out the source, into the ground plane, and back to
C
VCC
. To reduce any excess voltage ringing or spiking,
the inductance and area of this current loop must be
minimized.
FIGURE 5-1: Turn On Current Paths.
The charge needed to turn on the high-side power
MOSFET comes from the bootstrap capacitor C
BOOT
.
Current flows from C
BOOT
through the internal
HIGHDR circuitry, into the gate of the high-side power
MOSFET, out the source and back to C
BOOT
. The
printed circuit board traces that construct this current
loop need to have a small area and low inductance. To
control the inductance, short and wide traces must be
used.
Figure 5-2 depicts the current flow paths when the
outputs of the MCP14700 are low and the power
MOSFETs are turned off. These current paths should
also have low inductance and a small loop area to
minimize the voltage ringing and spiking.
FIGURE 5-2: Turn Off Current Paths.
The following recommendations should be followed for
optimal circuit performance:
- The components that construct the high
current paths previously mentioned should be
placed close the MCP14700 device. The
traces used to construct these current loops
should be wide and short to keep the
inductance and impedance low.
- A ground plane should be used to keep both
the parasitic inductance and impedance
minimized. The MCP14700 device is capable
of sourcing and sinking high peaks current
and any extra parasitic inductance or
impedance will result in non-optimal
performance.
V
CC
PWM
HI
C
VCC
C
BOOT
V
SUPPLY
MCP14700
PWM
LO
V
CC
PWM
HI
C
VCC
C
BOOT
V
SUPPLY
MCP14700
PWM
LO