SE98A Datasheet, PDF (28/43 Pages) NXP Semiconductors – DDR memory module temp sensor, 1.7 V to 3.6 V

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.
DIMM
DRAM
DRAM
SDA
SMBus
SPD
SE98A
SCL
DRAM
EVENT
MEMORY CONTROLLER
Fig 15. System application
DRAM
CPU
002aad760
9.2 Layout consideration
The SE98A does not require any additional components other than the host controller to
measure temperature. A 0.1 µF 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 °C.
Equation 1 is the formula to calculate the effect of self-heating:
SE98A_2
Product data sheet
∆T = R_{th( j-a)} ×
(1)
[(V _DD × I _{DD( AV )}) + (V _OL(SDA) × I _{OL( sink)(SDA)}) + (V _{OL(EVENT )} × I _{OL( sink)EVENT} )]
where:
∆T = 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
Rev. 02 — 6 August 2009
© NXP B.V. 2009. All rights reserved.
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