4
dc1815afc
DEMO MANUAL DC1815A
operation
Board Layout
Proper components placement and board layout with the
LTC4266A is important to provide electrical robustness and
correct operation. The following mentioned components,
also shown in Figure 3, must be close to their respective
LTC4266A pins with no other components in between on
the connection path. Place a 0.1µF capacitor (C1) directly
across VDD and DGND. Place a 1µF, 100V capacitor (C4)
and a SMAJ58A TVS (D3) directly across AGND and VEE.
Place the OUT 0.22µF, 100V capacitors (C22, C36, C47,
and C58) directly to their respective OUT pins all going
to an AGND plane.
The power path is from VEE to the sense resistor, to the
MOSFET, and out to the port. Select a trace width appro-
priate for the maximum current.
Kelvin sensing is necessary to provide accurate current
readings particularly with DC Disconnect. The sense resis-
tors used with the LTC4266A must be 0.25Ω, 1% or better,
and with a power rating that can handle the maximum DC
current passed through them. A dedicated sense trace
from each SENSE pin of the LTC4266A must go directly
to the respective sense resistor solder pad (Figure 4). Do
not connect to a copper area or trace between the sense
resistor and the MOSFET.
Figure 3. LTC4266A Key Application Components
for Board Placement
The VEE side of the sense resistor must connect to a thick
VEE plane through several large vias. At the LTC4266A,
the VEE pins and exposed pad tie together on the top layer
and connect to the VEE plane as well through its own
multiple large vias. The via size, number of vias, copper
thickness, trace width, and number of layers that connect
VEE between the sense resistors and the LTC4266A VEE
pins must total less than 15mΩ. A 2oz. copper thickness
for the VEE copper plane must be used if there is only a
single VEE plane connecting the LTC4266A VEE pins to
the sense resistors.
The VEE current path from the sense resistors to the
main VEE power supply must be either through a copper
plane, or a thick trace. If a trace is used, it must not pass
under the LTC4266A. Instead the path must go out to VEE
from the sense resistors as shown in Figure 4. The VEE
connection is from the VEE supply to the sense resistors
to the LTC4266A VEE pins and must stay in that order.
Figure 4. LTC4266A VEE Pins and Sense Resistors Connect to a
VEE Inner Layer Plane. A Kelvin Sense Trace from each SENSE
Pin Runs to the Respective Sense Resistor Pad. Connect the VEE
Supply Path to the Sense Resistors First, Then to the LTC4266A
VEE Pins
