RT9428WSC datasheet(12/14 Pages) RICHTEK

12 / 14 page

RT9428

DS9428-01

October 2014

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Figure 8. Derating Curve of Maximum Power Dissipation

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. For WL-CSP-

8B 1.6x1.52 (BSC) package, the thermal resistance,

θJA

is 114.4

°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) / (114.4°C/W) = 0.87W for

WL-CSP-8B 1.6x1.52 (BSC) package

The maximum power dissipation depends on the operating

ambient temperature for fixed TJ(MAX) and thermal

resistance,

θJA. The derating curve in Figure 8 allow the

designer to see the effect of rising ambient temperature

on the maximum power dissipation.

Table4. 2-Wire Protocol

Symbol

Description

Symbol

Description

START bit

Repeated START

SAddr

Slave address (7bit)

R/W

Read : R/W = 1; Write : R/W = 0

CAddr

Command address (byte)

STOP bit

Data

Data byte written by master

Data

Data byte returned by slave

Acknowledge bit written by master

Acknowledge bit returned by slave

No acknowledge bit written by master

No acknowledge bit returned by slave

0.0

0.2

0.4

0.6

0.8

1.0

100

125

Ambient Temperature (°C)

Four-Layer PCB

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