ADT7467 データシートの表示（PDF） - ON Semiconductor
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ADT7467 Datasheet PDF : 72 Pages
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ADT7467
Overtemperature Events
Overtemperature events on a temperature channel can be
automatically detected and dealt with in automatic fan speed
control mode. Register 0x6A to Register 0x6C contain the
THERM temperature limits. When a temperature exceeds
its THERM temperature limit, all PWM outputs run at the
maximum PWM duty cycle (0x38, 0x39, 0x3A); therefore,
fans run at the fastest speed allowed and continue running at
this speed until the temperature drops below THERM minus
hysteresis. (This can be disabled by setting the BOOST bit
in Configuration Register 3, Bit 2, Register 0x78.) The
hysteresis value for that THERM temperature limit is the
value programmed into Register 0x6D and Register 0x6E
(hysteresis registers). The default hysteresis value is 4C.
THERM LIMIT
TEMPERATURE
HYSTERESIS
(C)
FANS
100%
Figure 26. THERM Temperature Limit Operation
Limits, Status Registers, and Interrupts
Limit Values
High and low limits are associated with each
measurement channel on the ADT7467. These limits form
the basis of system-status monitoring in that a status bit can
be set for any out-of-limit condition and detected by polling
the device. Alternatively, SMBALERT interrupts can be
generated to flag a processor or microcontroller of
out-of-limit conditions.
8-bit Limits
The following is a list of 8-bit limits on the ADT7467.
Table 15. VOLTAGE LIMIT REGISTERS
Register
Description
0x46
0x47
0x48
0x49
VCCP Low Limit
VCCP High Limit
VCC Low Limit
VCC High Limit
Default
0x00
0xFF
0x00
0xFF
Table 16. THERM TIMER LIMIT REGISTERS
Register
Description
Default
0x7A
THERM Timer Limit
0x00
Table 17. TEMPERATURE LIMIT REGISTERS
Register
Description
Default
0x4E
Remote 1 Temperature Low Limit
0x01
0x4F
Remote 1 Temperature High Limit
0x7F
0x6A
Remote 1 THERM Limit
0xA4
0x50
0x51
0x6B
0x52
0x53
0x6C
Local Temperature Low Limit
Local Temperature High Limit
Local THERM Limit
Remote 2 Temperature Low Limit
Remote 2 Temperature High Limit
Remote 2 THERM Limit
0x01
0x7F
0xA4
0x01
0x7F
0xA4
16-bit Limits
The fan TACH measurements are 16-bit results. The fan
TACH limits are also 16 bits, consisting of a high byte and
low byte. Because slow or stalled fans are normally the only
conditions of interest, only high limits exist for fan TACHs.
Because the fan TACH period is measured, exceeding the
limit indicates a slow or stalled fan.
Table 18. FAN LIMIT REGISTERS
Register
Description
0x54
TACH1 Minimum Low Byte
0x55
0x56
0x57
0x58
0x59
0x5A
0x5B
TACH1 Minimum High Byte
TACH2 Minimum Low Byte
TACH2 Minimum High Byte
TACH3 Minimum Low Byte
TACH3 Minimum High Byte
TACH4 Minimum Low Byte
TACH4 Minimum High Byte
Default
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
0xFF
Out-of-Limit Comparisons
Once all limits are programmed, the ADT7467 can be
enabled for monitoring. The ADT7467 measures all voltage
and temperature measurements in round-robin format and
sets the appropriate status bit for out-of-limit conditions.
TACH measurements are not part of this round-robin cycle.
Comparisons are done differently, depending on whether the
measured value is being compared to a high or low limit.
High limit: > comparison performed
Low limit: comparison performed
Voltage and temperature channels use a window
comparator for error detecting and, therefore, have high and
low limits. Fan speed measurements use only a low limit.
This fan limit is needed only in manual fan control mode.
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