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LT3782A

3782af

3. The I2R losses in the sense resistor can be calculated

almost by inspection.

PR(SENSE) =

IO(MAX)

1– DMAX

•R •DMAX

4. The losses in the inductor are simply the DC input cur-

rent squared times the winding resistance. Expressing

this loss as a function of the output current yields:

PR(WINDING) =

IO(MAX)

1– DMAX

•RW

5. Losses in the boost diode. The power dissipation in the

boost diode is:

DIODE =

O(MAX)

•V

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 signiﬁcant at

low output voltages where the forward voltage is a

signiﬁcant percentage of the output voltage.

6. Other losses, including CIN and CO ESR dissipation and

inductor core losses, generally account for less than

2% of the total losses.

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 sufﬁcient. 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.

APPLICATIONS INFORMATION

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