LT3782A LINER [Linear Technology], LT3782A Datasheet - Page 15

• Manufacturer Part Number: LT3782A
• Description: 2-Phase Step-Up DC/DC Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
3. The I
4. The losses in the inductor are simply the DC input cur-
5. Losses in the boost diode. The power dissipation in the
6. Other losses, including C
almost by inspection.
rent squared times the winding resistance. Expressing
this loss as a function of the output current yields:
boost diode is:
The boost diode can be a major source of power loss
in a boost converter. For 13.2V input, 42V output at 3A,
a Schottky diode with a 0.4V forward voltage would
dissipate 600mW, which represents about 1% of the
input power. Diode losses can become signifi cant at
low output voltages where the forward voltage is a
signifi cant percentage of the output voltage.
inductor core losses, generally account for less than
2% of the total losses.
P
P
P
R(SENSE)
R(WINDING)
DIODE
2
R losses in the sense resistor can be calculated
=
I
O(MAX)
=
2
=
1– D
I
O(MAX)
1– D
I
O(MAX)
2
• V
MAX
2
D
MAX
IN
2
and C
• R • D
2
• R
O
W
MAX
ESR dissipation and
PCB Layout Considerations
To achieve best performance from an LT3782A circuit, the
PC board layout must be carefully done. For lower power
applications, a two-layer PC board is suffi cient. However,
at higher power levels, a multiplayer PC board is recom-
mended. Using a solid ground plane under the circuit is
the easiest way to ensure that switching noise does not
affect the operation.
In order to help dissipate the power from MOSFETs and
diodes, keep the ground plane on the layers closest to the
layers where power components are mounted. Use power
planes for MOSFETs and diodes in order to improve the
spreading of the heat from these components into the
PCB.
For best electrical performance, the LT3782A circuit should
be laid out as follows:
Place all power components in a tight area. This will
minimize the size of high current loops. Orient the input
and output capacitors and current sense resistors in a way
that minimizes the distance between the pads connected
to ground plane.
Place the LT3782A and associated components tightly to-
gether and next to the section with power components.
Use a local via to ground plane for all pads that connect to
ground. Use multiple vias for power components.
Connect the current sense inputs of LT3782A directly
to the current sense resistor pads. Connect the current
sense traces on the opposite sides of pads from the traces
carrying the MOSFETs source currents to ground. This
technique is referred to as Kelvin sensing.
LT3782A
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3782af