ADT7476
Rev. B | Page 24 of 72
The fans run 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 the THERM temperature limit is the
value programmed into the hysteresis registers (Register 0x6D
and Register 0x6E). The default hysteresis value is 4°C.
Single-Channel ADC Conversions
Setting Bit 6 of Configuration Register 2 (0x73) places the
ADT7476 into single-channel ADC conversion mode. In this
mode, the ADT7476 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 14. Programming Single-Channel ADC Mode for
Temperatures
Register 0x55, Bits [7:5]
Channel Selected
101
Remote 1 temperature
110 Local
temperature
111
Remote 2 temperature
FANS
TEMPERATURE
100%
HYSTERESIS (°C)
THERM LIMIT
05
38
2-
0
29
Configuration Register 2 (0x73)
Figure 28. THERM Temperature Limit Operation
Bit 4 = 1, averaging off.
THERM can be disabled on specific temperature channels using
Bits [7:5] of Configuration Register 5 (0x7C). THERM can also
be disabled by:
Bit 6 = 1, single-channel convert mode.
TACH1 Minimum High Byte (0x55)
Bits [7:5] selects ADC channel for single-channel convert mode.
•
In Offset 64 mode, writing −64°C to the appropriate
THERM temperature limit
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 speed allowed.
•
In twos complement mode, writing −128°C to the
appropriate THERM temperature limit
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