CM313202SB Ver la hoja de datos (PDF) - California Micro Devices Corp

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CM313202SB

Triple Linear Voltage Regulator for DDR-I Memory and CPU

California Micro Devices Corp 

PRELIMINARY

CM3132

Performance Information (cont’d)

Typical Thermal Characteristics

The overall junction to ambient thermal resistance

(θJA) for device power dissipation (PD) consists prima-

rily of two paths in series. The first path is the junction

to the case (θJC) which is defined by the package style,

and the second path is case to ambient (θCA) thermal

resistance which is dependent on board layout. The

final operating junction temperature for any set of con-

ditions can be estimated by the following thermal equa-

tion:

TJUNC = TAMB + PD ( θJC ) + PD ( θCA )

= TAMB + PD ( θJA)

When a CM3132-02SB (PSOP-8) is mounted on a

double-sided printed circuit board with two square

inches of copper allocated for "heat spreading," the

resulting θJA is 40°C/W. Based on the over tempera-

ture limit of 150° C with an ambient of 70°C, the avail-

able power of this package will be:

PD = -1---5---0-4---°0----C°----C-–---/--7--W-0----°----C-- = 2W

PCB Layout Considerations

The CM3132-02SB/SH has a heat spreader attached

to the bottom of the PSOP-8 package in order for heat

to be transferred more easily from the package to the

PCB. The heat spreader is a copper pad of dimensions

just smaller than the package itself. By positioning the

matching pad on the PCB top layer to connect to the

spreader during manufacturing, the heat will be trans-

ferred between the two pads. The drawing below

shows the recommended PCB layout. Note that there

are six vias on either side to allow the heat to dissipate

into the ground and power planes on the inner layers of

the PCB. Vias can be placed underneath the chip, but

this can cause blockage of the solder. The ground and

power planes should be at least 2 sq in. of copper by

the vias. It also helps dissipation if the chip is posi-

tioned away from the edge of the PCB, and not near

other heat-dissipating devices. A good thermal link

from the PCB pad to the rest of the PCB will assure the

best heat transfer from the CM3132 package to ambi-

ent, θJA, of around 40°C/W.

Figure 4. Recommended Heat Sink PCB Layout

© 2004 California Micro Devices Corp. All rights reserved.

8 430 N. McCarthy Blvd., Milpitas, CA 95035-5112 ● Tel: 408.263.3214 ● Fax: 408.263.7846 ● www.calmicro.com 10/13/04

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