SE98ATP,547【PDF 28/43 页】IC TEMP SENSOR DDR 8-HWSON

SE98A_4

Product data sheet

Rev. 04 25 November 2009

28 of 43

NXP Semiconductors

SE98A

DDR memory module temp sensor, 1.7 V to 3.6 V

9.1 SE98A in memory module application

Figure 15

shows the SE98A being placed in the memory module application with the

SPD. The SE98A is centered in the memory module to provide the function to monitor the

temperature of the DRAM. In the event of overheat, the SE98A triggers the EVENT

output

and the memory controller can throttle the memory bus to slow the DRAM, or the CPU can

increase the refresh rate for the DRAM. The memory controller can also read the SE98A

and watch the DRAM thermal behavior.

9.2 Layout consideration

The SE98A does not require any additional components other than the host controller to

measure temperature. A 0.1 糉 bypass capacitor between the V

DD

and V

SS

pins is

located as close as possible to the power and ground pins for noise protection.

9.3 Thermal considerations

In general, self-heating is the result of power consumption and not a concern, especially

with the SE98A, which consumes very low power. In the event the SDA and EVENT

pins

are heavily loaded with small pull-up resistor values, self-heating affects temperature

accuracy by approximately 0.5 癈.

Equation 1

is the formula to calculate the effect of self-heating:

(1)

where:

擳 = T

j

T

amb

T

j

= junction temperature

T

amb

= ambient temperature

R

th(j-a)

= package thermal resistance

V

DD

= supply voltage

I

DD(AV)

= average supply current

V

OL(SDA)

= LOW-level output voltage on pin SDA

V

OL(EVENT)

= LOW-level output voltage on pin EVENT

Fig 15. System application

002aad76

SE98A

EVENT

DIMM

DRAM

MEMORY CONTROLLER

SMBus

CPU

SPD

SDA

SCL

?SPAN class="pst SE98ATP-547_2307474_14">T R

th j-a

( )

V

DD

I

DD AV

( )

?/DIV>

(

) V

OL SDA

(

)

I

OL

k

sin

(

) SDA

(

)

?/DIV>

(

) V

OL EVENT

(

)

I

OL

k

sin

(

)EVENT

?/DIV>

(

)

+

[

]

?/DIV>

=

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