ADT7473 查看數據表（PDF） - ON Semiconductor
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ADT7473 Datasheet PDF : 74 Pages
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ADT7473
THERM LIMIT
TEMPERATURE
HYSTERESIS (5C)
FANS
100%
Figure 28. THERM Limit Operation
Limits, Status Registers, and Interrupts
Limit Values
Associated with each measurement channel on the
ADT7473/ADT7473−1 are high and low limits. These can
form the basis of system status monitoring; a status bit can
be set for any out−of−limit condition and is 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 ADT7473/
ADT7473−1.
Voltage Limit Registers
Register 0x46, VCCP Low Limit = 0x00 default
Register 0x47, VCCP High Limit = 0xFF default
Register 0x48, VCC Low Limit = 0x00 default
Register 0x49, VCC High Limit = 0xFF default
Temperature Limit Registers
Register 0x4E, Remote 1 Temperature Low Limit = 0x01
default
Register 0x4F, Remote 1 Temperature High Limit = 0xFF
default
Register 0x6A, Remote 1 THERM Limit = 0xA4 default
Register 0x50, Local Temperature Low Limit = 0x01 default
Register 0x51, Local Temperature High Limit = 0xFF default
Register 0x6B, Local THERM Temperature Limit = 0xA4
default
Register 0x52, Remote 2 Temperature Low Limit = 0x01
default
Register 0x53, Remote 2 Temperature High Limit = 0xFF
default
Register 0x6C, Remote 2 THERM Temperature Limit = 0xA4
default
THERM Limit Register
Register 0x7A, THERM Timer Limit = 0x00 default
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 fans running under speed or stalled are
normally the only conditions of interest, only high limits
exist for fan TACHs. Because the fan TACH period is
actually being measured, exceeding the limit indicates a
slow or stalled fan.
Fan Limit Registers
Register 0x54, TACH1 Minimum Low Byte = 0xFF default
Register 0x55, TACH1 Minimum High Byte = 0xFF default
Register 0x56, TACH2 Minimum Low Byte = 0xFF default
Register 0x57, TACH2 Minimum High Byte = 0xFF default
Register 0x58, TACH3 Minimum Low Byte = 0xFF default
Register 0x59, TACH3 Minimum High Byte = 0xFF default
Register 0x5A, TACH4 Minimum Low Byte = 0xFF default
Register 0x5B, TACH4 Minimum High Byte = 0xFF default
Out−of−Limit Comparisons
Once all limits have been programmed, the ADT7473/
ADT7473−1 can be enabled for monitoring. The ADT7473/
ADT7473−1 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.
Analog Monitoring Cycle Time
The analog monitoring cycle begins when a 1 is written to
the start bit (Bit 0) of Configuration Register 1 (0x40). By
default, the ADT7473/ADT7473−1 powers up with this bit
set. The ADC measures each analog input in turn and, as
each measurement is completed, the result is automatically
stored in the appropriate value register. This round−robin
monitoring cycle continues unless disabled by writing a 0 to
Bit 0 of Configuration Register 1.
As the ADC is normally left to free−run in this manner, the
time taken to monitor all the analog inputs is normally not
of interest, because the most recently measured value of any
input can be read out at any time.
For applications where the monitoring cycle time is
important, it can easily be calculated. The total number of
channels measured is
• One dedicated supply voltage input (VCCP)
• Supply voltage (VCC pin)
• Local temperature
• Two remote temperatures
As mentioned previously, the ADC performs round−robin
conversions. The total monitoring cycle time for averaged
voltage and temperature monitoring is 146 ms. The total
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