Board Layout - Linear Technology 1814A Demo Manual

BoarD Layout

Proper components placement and board layout with
respect to the LTC4274A is important to provide electrical
robustness and correct operation. The following mentioned
components, also shown in Figure 2, must be close to their
respective LTC4274A pins with no other components in
between on the connection path. Place a 0.1µF capacitor
(C1) directly across the LTC4274A VDD and DGND pins.
Place a 1µF , 100V capacitor (C4) and a SMAJ58A TVS (D3)
directly across the LTC4274A AGND and VEE pins. Place
a 0.22µF , 100V capacitor (C5) directly to the OUT pin and
an AGND plane.
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13
VDD VDD
C1
0.1µF
10
DGND
DGND
15
DGND
16
DGND
17
DGND
18
D3
SMAJ58A
VEE
Figure 2. LTC4274A Key Application Components for Board Placement
Figure 3. LTC4274IUHF VEE and SENSE Kelvin Connection to Sense Resistor
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. The sense resistor used with the LTC4274A must
be 0.25Ω, 1% or better, and with a power rating that can
handle the maximum DC current passed through it. A
dedicated sense trace from the SENSE pin of the LTC4274A
must go directly to the sense resistor solder pad. Avoid
connecting to copper cutouts and other traces. The VEE
side of the sense resistor must also connect to the VEE
pins of the LTC4274A either through a direct trace (Figure
3A), or a VEE copper plane (Figure 3B), without any other
components in between on this connection.
U1
LTC4274AIUHF
19 22 25 26 27 39 30
C4
0.1µF
RS1
100V
0.25
Q1
CSRN2512FKR250
FDMC86102
DEMO MANUAL
DC1814A
31 32
C5
0.22µF
100V
OUT
DC1814A F02
dc1814afe
3