ADT7476 Analog Devices, Inc., ADT7476 Datasheet - Page 30

• Manufacturer Part Number: ADT7476
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADT7476
Configuring the Relevant THERM Behavior
1.
2.
3.
4.
5.
Configure the desired pin as the THERM timer input.
Setting Bit 1 ( THERM timer enable) of Configuration
Register 3 (0x78) enables the THERM timer monitoring
functionality. This is disabled on Pin 14 and Pin 22 by
default.
Setting Bit 0 and Bit 1 (Pin14Func of Configuration
Register 4 (0x7D) enables THERM timer output
functionality on Pin 22 (Bit 1 of Configuration Register 3,
THERM , must also be set). Pin 14 can also be used as
TACH4.
Select the desired fan behavior for THERM timer events.
Assuming that the fans are running, setting Bit 2 (BOOST
bit) of Configuration Register 3 (0x78) causes all fans to
run at 100% duty cycle whenever THERM is asserted. This
allows fail-safe system cooling. If this bit is 0, the fans run
at their current settings and are not affected by THERM
events. If the fans are not already running when THERM is
asserted, the fans do not run to full speed.
Select whether THERM timer events should generate
SMBALERT interrupts.
When set, Bit 5 (F4P) of Interrupt Mask Register 2 (0x75)
or Bit 0 of Interrupt Mask Register 1 (0x74), depending on
which pins are configured as a THERM timer, masks out
the SMBALERT when the THERM timer limit value is
exceeded. This bit should be cleared if the SMBALERT
based on THERM events are required.
Select a suitable THERM limit value.
This value determines whether an SMBALERT is generated
on the first THERM assertion or only if a cumulative
THERM assertion time limit is exceeded. A value of 0x00
causes an SMBALERT to be generated on the first THERM
assertion.
Select a THERM monitoring time.
This value specifies how often OS- or BIOS-level software
checks the THERM timer. For example, BIOS can read the
THERM timer once an hour to determine the cumulative
THERM assertion time. If, for example, the total THERM
assertion time is <22.76 ms in Hour 1, >182.08 ms in Hour 2,
and >5.825 sec in Hour 3, this indicates that system per-
formance is degrading significantly because THERM is
asserting more frequently on an hourly basis.
Rev. B | Page 30 of 72
Configuring the THERM Pin as an Output
In addition to monitoring THERM as an input, the ADT7476 can
optionally drive THERM low as an output. When PROCHOT is
bidirectional, THERM can be used to throttle the processor by
asserting PROCHOT . The user can preprogram system-critical
thermal limits. If the temperature exceeds a thermal limit by
0.25°C, THERM asserts low. If the temperature is still above the
thermal limit on the next monitoring cycle, THERM stays low.
THERM remains asserted low until the temperature is equal to
or below the thermal limit. Because the temperature for that
channel is measured only once for every monitoring cycle, after
THERM asserts it is guaranteed to remain low for at least one
monitoring cycle.
The THERM pin can be configured to assert low, if the
Remote 1, local, or Remote 2 THERM temperature limits are
exceeded by 0.25°C. The THERM temperature limit registers
are at Register 0x6A, Register 0x6B, and Register 0x6C,
respectively. Setting Bits [7:5] of Configuration Register 5 (0x7C)
enables the THERM output feature for the Remote 2, local, and
Remote 1 temperature channels, respectively. Figure 34 shows
how the THERM pin asserts low as an output in the event of a
critical overtemperature.
An alternative method of disabling THERM is to program the
THERM temperature limit to –63°C or less in Offset 64 mode,
or −128°C or less in twos complement mode; that is, for
THERM temperature limit values less than −63°C or −128°C,
respectively, THERM is disabled.
Figure 34. Asserting THERM as an Output, Based on Tripping THERM Limits
THERM
THERM LIMIT
THERM LIMIT
Alternatively, OS- or BIOS-level software can timestamp
when the system is powered on. If an SMBALERT is gen-
erated due to the THERM timer limit being exceeded,
another timestamp can be taken. The difference in time
can be calculated for a fixed THERM timer limit time. For
example, if it takes one week for a THERM timer limit of
2.914 seconds to be exceeded, and the next time it takes
only 1 hour, this is an indication of a serious degradation in
system performance.
0.25°C
TEMP
MONITORING
CYCLE