RT8288A datasheet(12/14 Pages) RICHTEK

12 / 14 page

RT8288A

DS8288A-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

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.

Layout Considerations

Follow the PCB layout guidelines for optimal performance

of the IC.

Keep the traces of the main current paths as short and

wide as possible.

Put the input capacitor as close as possible to the device

pins (VIN and GND).

SW node is with high frequency voltage swing and

should be kept at small area. Keep analog components

away from the SW node to prevent stray capacitive noise

pickup.

Connect feedback network behind the output capacitors.

Keep the loop area small. Place the feedback

components near the IC.

Figure 6. Derating Curve of Maximum Power Dissipation

VIN

VCC

BOOT

2, 3

VOUT

VIN

RT8288A

CBOOT

COUT

CIN

GND

8, 9 (Exposed Pad)

CS*

RS*

REN*

CEN*

* : Optional

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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