RT8288 datasheet(12/14 Pages) RICHTEK

12 / 14 page

RT8288

DS8288-03

June 2012

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Figure 5. Reference Circuit with Snubber and Enable Timing Control

Thermal Considerations

For continuous operation, do not exceed absolute

maximum junction temperature. The maximum power

dissipation depends on the thermal resistance of the IC

package, PCB layout, rate of surrounding airflow, and

difference between junction and ambient temperature. The

maximum power dissipation can be calculated by the

following formula :

PD(MAX) = (TJ(MAX)

− TA) / θJA

where TJ(MAX) is the maximum junction temperature, TA is

the ambient temperature, and

θJAis the junction to ambient

thermal resistance.

For recommended operating condition specifications, the

maximum junction temperature is 125

°C. The junction to

ambient thermal resistance,

θJA, is layout dependent. For

SOP-8 (Exposed Pad) package, the thermal resistance,

θJA, is 75°C/W on a standard JEDEC 51-7 four-layer

thermal test board. The maximum power dissipation at TA

= 25

°C can be calculated by the following formula :

PD(MAX) = (125

°C − 25°C) / (75°C/W) = 1.333W for

SOP-8 (Exposed Pad) package

Figure 6. Derating Curve of Maximum Power Dissipation

VIN

VCC

BOOT

2, 3

VOUT

VIN

RT8288

CBOOT

COUT

CIN

GND

8, 9 (Exposed Pad)

CS*

RS*

REN*

CEN*

* : Optional

reducing the SW trace area and keeping the main power

in a small loop will be helpful on EMI performance. For

detailed PCB layout guide, please refer to the section

Layout Considerations.

The maximum power dissipation depends on the operating

ambient temperature for fixed TJ(MAX) and thermal

resistance,

θJA. The derating curve in Figure 6 allows the

designer to see the effect of rising ambient temperature

on the maximum power dissipation.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

100

125

Ambient Temperature (°C)

Four-Layer PCB

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