LT3782AIFE(RevC) Просмотр технического описания (PDF) - Linear Technology

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LT3782AIFE
(Rev.:RevC)

2-Phase Step-Up DC/DC Controller

Linear Technology 

LT3782A

APPLICATIONS INFORMATION

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

almost by inspection:

PR(SENSE)

=

⎛

⎜

⎜

⎝⎜⎜

IO(MAX )

2

1– DMAX

⎞2

⎟

⎟

⎠⎟⎟

•

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 )

2

1– DMAX

⎞2

⎟

⎟

⎠⎟⎟

•

RW

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

boost diode is:

PDIODE

=

IO(MAX )

2

•

VD

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 recommended. 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

together 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.

14

For more information www.linear.com/LT3782A

3782afc

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