adt7476a Analog Devices, Inc., adt7476a Datasheet - Page 28

• Manufacturer Part Number: adt7476a
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

ADT7476A
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 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,
then the fans do not run to full speed.
Select whether THERM timer events should generate
SMBALERT interrupts.
Setting Bit 5 (F4P) of Mask Register 2 (0x75) or Bit 0 of
Mask Register 1 (0x74), depending on which pins are
configured as a THERM timer, masks SMBALERT s when
the THERM timer limit value is exceeded. This bit should be
cleared if SMBALERT s 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 if only 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 s in Hour 3, system performance is degrading
significantly because THERM is asserting more frequently
on an hourly basis.
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Configuring the THERM Pin as an Output
In addition to monitoring THERM as an input, the ADT7476A
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 [5:7] of Configuration Register 5 (0x7C)
enables the THERM output feature for the Remote 1, local, and
Remote 2 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 generated 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 sec to be exceeded,
and the next time it takes only 1 hour, then a serious
degradation in system performance has occurred.
0.25°C
TEMP
MONITORING
CYCLE