NCP1580

http://onsemi.com

10

Thermal Considerations

The power dissipation of the NCP1580 varies with the

average MOSFET gate current typically dominates the

control IC power dissipation. The IC power dissipation is

determined by the formula:

PIC + (ICC

VCC) ) PTG ) PBG.

Where:

The upper (switching) MOSFET gate driver losses are:

PTG + QTG

fSW

VBST.

Where:

The lower (synchronous) MOSFET gate driver losses are:

PBG + QBG

fSW

VCC.

Where:

The junction temperature of the control IC can then be

calculated as:

TJ + TA ) PIC

qJA.

Where:

IC package.

from the specifications section of this data sheet and a

calculation can be made to determine the IC junction

temperature.

In

addition,

a

thermal

resistance

(Junction−to−Ambient/SafeOperating Area) curve has been

included below to further aid design. 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.

165

155

145

135

125

175

0

50 100 150 200 250 300 350 400

Figure 16. Thermal Resistance

(Junction−to−Ambient/Safe Operating Area)

115

1 oz cu

450 500 550 600 650

0.595

0.620

0.645

0.670

0.695

0.720

0.745

0.770

0.795

0.820

0.570

0.845

0.870

2 oz cu