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CM3107

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

California Micro Devices Corp 

CM3107

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 CM3107-00SN (SOIC) is mounted on a double

sided printed circuit board with two square inches of

copper allocated for "heat spreading", the resulting θJA

is 151°C/W. Based on the over temperature limit of

150°C with an ambient of 85°C, the available power of

this package will be:

PD = (150°C -85°C) / 151°C/W = 0.43W

For the CM3107-00SB (PSOP), the θJA is 40°C/W and

the available power for this package will be:

PD = (150°C -85°C) / 40°C/W = 0.1.625W

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

0.344A for CM3107-00SN and 1.3A for CM3107-00SB.

The maximum instantaneous current is specified at 2A,

so this condition should not be exceeded 17% and

65% of the time for CM3107-00SN and CM3107-00SB,

respectively. 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

17% (SOIC) and 65% (PSOP) 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 0.73W

for CM3107-00SN and 2.75W for CM3107-00SB. So

the maximum average RMS current increases from

0.42A to 0.58A for CM3107-00SN and maximum

instantaneous current of 2A should not be exceeded

29% of the time. For CM3107-00SB, the maximum

RMS current increases from 1.3A to 2.2A. Thus, the

maximum continuous current can be 2A all the time.

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 L Tel: 408.263.3214

L Fax: 408.263.7846 L www.calmicro.com

02/02/04

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