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System Memory Design Guidelines (DDR-SDRAM)
7.7.
External Thermal Sensor Based Throttling (ETS#)
The Intel 852GM chipset GMCH's ETS# input pin is an active low input that can be used with an
external thermal sensor to monitor the temperature of the DDR SO-DIMMs for a possible thermal
condition. Assertion of ETS# will result in the limiting of DRAM bandwidth on the DDR memory
interface to reduce the temperature in the vicinity of the system memory.
By default, the functionality and input buffer associated with ETS# are disabled. Also, the GMCH can
be programmed to send an SERR, SCI, or SMI message to the ICH4-M upon the assertion of this signal.
External thermal sensors that are suitable for the purpose described above would need to have a small
form factor and be able to accurately monitor the ambient temperature in the vicinity of the DDR system
memory.
Intel is currently in the process of enabling this feature on the Intel 852GM GMCH and is actively
engaging with thermal sensor vendors to ensure compatibility and suitability of vendors' products with
the ETS# pin. This includes electrical design guidelines for the ETS# pin and usage/placement
guidelines of the thermal sensors for maximum effectiveness. Current third party vendor product
offerings that may be suitable for the ETS# pin application include ambient temperature thermal sensors
and remote diode thermal sensors. Also, thermal sensors that implement an open-drain output for
signaling a thermal event would provide the most flexibility from an electrical and for layout design
perspective.
The design guidelines for ETS# and external thermal sensor placement below are considered
preliminary and subject to change in future revisions of this design guide. Please contact your local FAE
for any updates.
7.7.1.
ETS# Usage Model
The thermal sensors targeted for this application with the GMCH's ETS# are planned to be capable of
measuring the ambient temperature only and should be able to assert ETS# if the preprogrammed
thermal limits/conditions are met or exceeded. Because many variables within a mobile system can
affect the temperature measured at any given point in a system, the expected usage and effectiveness of
ETS# is also very focused. Because of factors such as thermal sensor placement, airflow within a mobile
chassis, adjacent components, thermal sensor sensitivity, and thermal sensor response time, ETS# can
effectively be used for controlling skin temperatures. However, ETS# should not be used for measuring
or controlling the Tj or Tcase parameters of DDR-SDRAM devices since due to the location of the
thermal sensor it cannot respond quickly enough to dynamic changes in DRAM power.
7.7.2.
ETS# Design Guidelines
ETS#, as implemented in the GMCH, is an active low signal and does not have an integrated pull-up to
maintain a logic 1. As a result of this, a placeholder for an external 8.2 kΩ to 10 kΩ pull-up resistor
should be provided near the ETS# pin. Electrical details on output characteristics of suitable thermal
sensors for use with the GMCH are currently not finalized. The currently recommended pull-up voltage
for this external pull-up should be 3.3 V. The thermal sensor should implement an open drain type
output buffer to drive ETS#. A system is expected to have one thermal sensor per SO-DIMM connector
on the motherboard. As a result, routing guidelines for the output of these thermal sensors to the ETS#
pin will also be important.
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Intel
852GM Chipset Platform Design Guide
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