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Single-channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (0x73) places
the ADT7476A into single-channel ADC conversion mode.
In this mode, the ADT7476A can be made to read a single
temperature channel only. The appropriate ADC channel is
selected by writing to Bits [7:5] of the TACH1 minimum
high byte register (0x55).
Table 22. PROGRAMMING SINGLE-CHANNEL ADC
MODE FOR TEMPERATURES
Bits [7:5], Register 0x55
101
110
111
Table 23. CONFIGURATION REGISTER 2 (REG. 0x73)
Bit
[4]
[6]
TACH1 Minimum High Byte (0x55)
[7:5] selects ADC channel for single-channel convert mode.
Overtemperature Events
Overtemperature events on any of the temperature
channels can be detected and dealt with automatically in
automatic fan speed control mode. Register 0x6A to
Register 0x6C are the THERM temperature limits. When a
temperature exceeds its THERM temperature limit, all
PWM outputs run at the maximum PWM duty cycle
(Register 0x38, Register 0x39, and Register 0x3A).
This effectively runs the fans at the fastest allowed speed.
The fans run at this speed until the temperature drops
below THERM minus hysteresis. This can be disabled by
setting Bit 2, the boost bit, in Configuration Register 3
(0x78). The hysteresis value for the THERM temperature
limit is the value programmed into the hysteresis registers
(0x6D and 0x6E). The default hysteresis value is 4°C.
THERM LIMIT
TEMPERATURE
FANS
Figure 28. THERM Temperature Limit Operation
THERM can be disabled on specific temperature channels
using Bits [7:5] of Configuration Register 5 (0x7C).
THERM can also be disabled by:
•
Writing −64°C to the appropriate THERM temperature
limit in Offset 64 mode.
•
Writing −128°C to the appropriate THERM
temperature limit in twos complement mode.
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Channel Selected
Remote 1 Temperature
Local Temperature
Remote 2 Temperature
Description
1: Averaging Off
1: Single-channel Convert Mode
HYSTERESIS (°C)
100%
ADT7476A
Limits, Status Registers, and Interrupts
Limit Values
Associated with each measurement channel on the
ADT7476A 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 out-of-limit conditions to a processor
or microcontroller.
8-bit Limits
The following is a list of 8-bit limits on the ADT7476A.
Table 24. VOLTAGE LIMIT REGISTERS
Register
0x44
0x45
0x46
0x47
0x48
0x49
0x4A
0x4B
0x4C
0x4D
Table 25. TEMPERATURE LIMIT REGISTERS
Register
0x4E
Remote 1 Temperature Low Limit
0x4F
Remote 1 Temperature High Limit
0x6A
Remote 1 THERM Temp. Limit
0x50
Local Temperature Low Limit
0x51
Local Temperature High Limit
0x6B
Local THERM Temperature Limit
0x52
Remote 2 Temperature Low Limit
0x53
Remote 2 Temperature High Limit
0x6C
Remote 2 THERM Temp. Limit
Table 26. THERM TIMER LIMIT REGISTER
Register
0x7A
THERM Timer Limit
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.
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20
Description
Default
2.5 V Low Limit
0x00
2.5 V High Limit
0xFF
V
Low Limit
0x00
CCP
V
High Limit
0xFF
CCP
V
Low Limit
0x00
CC
V
High Limit
0xFF
CC
5.0 V Low Limit
0x00
5.0 V High Limit
0xFF
12 V Low Limit
0x00
12 V High Limit
0xFF
Description
Default
0x81
0x7F
0x64
0x81
0x7F
0x64
0x81
0x7F
0x64
Description
Default
0x00
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