CM3109-00SH Ver la hoja de datos (PDF) - California Micro Devices Corp

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CM3109-00SH

2A Sink/Source Regulator for Front Side Bus and DDR Memory Bus Termination

California Micro Devices Corp 

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 CM3109-00SB/SH (PSOP) 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 85°C, the avail-

able power of this package will be:

PD = (150°C -85°C) / 40°C/W = 1.625W

DDR Memory Application

Since the output voltage is 1.25V, and the device can

either source current from VDDQ or sink current to

Ground, the power dissipated in the device at any time

is 1.25V times the current load. This means the maxi-

mum average RMS current (in either direction) is 1.3A

for CM3109-00SB/SH. The maximum instantaneous

current is specified at 2A, so this condition should not

be exceeded 65% of the time. It is highly unlikely in

most usage of DDR memory that this might occur,

because it means the DDR memory outputs are either

all high or all low for 65% of the time.

If the ambient temperature is 40°C instead of 85°C,

which is typically the maximum in most DDR memory

applications, the power dissipated (PD) can be 2.75W.

So the maximum RMS current increases from 1.3A to

2.2A. Thus, the maximum continuous current can be

2A all the time.

CM3109

Figure 12. Duty Cycle vs. Ambient

Temperature (ILOAD = 2A)

Figure 13. Duty Cycle vs. Output

Current (Temp=70°C)

© 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

01/15/04

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