NCP1579

http://onsemi.com

10

The upper (switching) MOSFET gate driver losses are:

Where:

The lower (synchronous) MOSFET gate driver losses are:

Where:

The junction temperature of the control IC can then be

calculated as:

Where:

IC package.

The package thermal resistance can be obtained from the

specifications section of this data sheet and a calculation can

be made to determine the IC junction temperature. However,

it should be noted that the physical layout of the board, the

proximity of other heat sources such as MOSFETs and

inductors, and the amount of metal connected to the IC,

impact the temperature of the device. Use these calculations

as a guide, but measurements should be taken in the actual

application.

Layout Considerations

As in any high frequency switching converter, layout is

very important. Switching current from one power device to

another can generate voltage transients across the

impedances of the interconnecting bond wires and circuit

traces. These interconnecting impedances should be

minimized by using wide, short printed circuit traces. The

critical components should be located as close together as

possible using ground plane construction or single point

grounding. The figure below shows the critical power

components of the converter. To minimize the voltage

overshoot the interconnecting wires indicated by heavy lines

should be part of ground or power plane in a printed circuit

board. The components shown in the figure below should be

located as close together as possible. Please note that the

capacitors. It is desirable to locate the NCP1579 within 1

inch of the MOSFETs, Q1 and Q2. The circuit traces for the

MOSFETs’ gate and source connections from the NCP1579

must be sized to handle up to 2 A peak current.

Figure 12. Components to be Considered for

Layout Specifications

NCP1579