RT4532WSC datasheet(11/12 Pages) RICHTEK

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RT4532

DS4532-01 August 2015

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

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, TAis

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

WL-CSP-10B 0.87x2.07 (BSC) package, the thermal

resistance,

θJA, is 99.6°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) / (99.6°C/W) = 1W for

WL-CSP-10B 0.87x2.07 (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 1 allows the

designer to see the effect of rising ambient temperature

on the maximum power dissipation.

Layout Consideration

As for all switching power supplies, the layout is an

important step in the design, especially at high peak

currents and switching frequencies. If the layout is not

carefully done, the regulator might expose noise problems

and duty cycle jitter. Therefore, use wide and short traces

for high current paths. The input capacitor should be placed

as close as possible to the input pin for good input voltage

filtering. The inductor should be placed as close as possible

to the switch pin to minimize the noise coupling into other

circuits. The output capacitor needs to be placed directly

from the VOUT pin to GND rather than across the LEDs.

This reduces the ripple current in the trace to the LEDs.

When doing the PCB layout, the bold traces should be

routed first, as well as placement of the inductor, and input

and output capacitors.

Figure 1. Derating Curve of Maximum Power Dissipation

0.0

0.2

0.4

0.6

0.8

1.0

1.2

100

125

Ambient Temperature (°C)

Four-Layer PCB

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