Analog Devices ADT7460 Manual page 45

Table 63. T Registers
MIN
Register Address
0x67
0x68
0x69
These are the T registers for each temperature channel. When the temperature measured exceeds T
MIN
minimum speed and increase with temperature according to T
These r egisters become read-only when the Configuration Register 1 lock bit is set. Further attempts to write to these registers have no
e ffect.
Table 64. THERM Limit Registers
Register Address
0x6A
0x6B
0x6C
If any temperature measured exceeds its THERM limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail-safe mechanism
inco rporated to cool the system in the event of a critical overtemperature. It also ensures some level of cooling in the event that software
o r hardware locks up. If set to 0x80, this feature is disabled. The PWM output remains at 100% until the temperature drops below
Limit – Hysteresis. If the THERM pin is programmed as an output, exceeding these limits by 0.25°C can cause the THERM pin
T HERM
to assert low as an output.
These registers become rea -only when the Configuration Register 1 Lock bit is s d
no effect.
Table 65. Temperature Hysteresis Registers
Register Address
0x6D
0x6E
Each 4-bit value controls the amount of temperature hysteresis applied to a particular temperature channel. Once the temperature for that
channel falls below its T value, the fan remains running at PWM
MIN
hysteresis may be assigned to any temperature channel. The hysteresis value chosen also applies to that temperature channel if its THERM
limit is exceeded. The PWM output being controlled goes to 100% if the THERM limit is exceeded and remains at 100% until the
temperature drops below THERM – Hysteresis. For acoustic reasons, it is recommended that the hysteresis value not be programmed less
than 4°C. Setting the hysteresis value lower than 4°C causes the fan to switch on and off regularly when the temperature is close to T
These registers become read-only when the Configuration Register 1 lock bit is set to 1. Further attempts to write to these registers have
no effect.
Table 66. XNOR Tree Test Enable Register (Power-On Default = 0x00)
Register Address R/W
0x6F Read/Write
This register becomes read-only when the Configuration Register 1 lock bit is set to 1. Further attempts to write to this register have no
effect.
R/W
Read /Write
Read/Write
Read/Write
R/W
Read/Write
Read/Write
Read/Write
R/W Description
Read/Write Remote 1 Local Temperature Hysteresis
Read/Write Remote 2 Temperature Hysteresis
Description
XNOR Tree Test Enable
Bit Mnmeonic
<0> XEN
<7:1> RES
Description
Remote 1 T emperature T
MIN
Local Temperature T
MIN
Remote 2 Temperature T
MIN
.
RANGE
Descrip tion
Remote 1 THERM Limit
Local THERM Limit
Remote 2 THERM Limit
et to 1. Further attempts to write to these registers have
duty cycle until the temperature = T
MIN
Description
If the XEN bit is set to 1, the device enters the XNOR tree test mode.
Clearing the bit removes the device from the XNOR test mode.
Unused. Do not write to these bits.
Rev. C | Page 45 of 52
ADT7460
Power-On Default
0x5A (90°C)
0x5A (90°C)
0x5A (90°C)
, the appropriate fan runs at
MIN
Power-On Default
0x64 (100°C)
0x64 (100°C)
0x64 (100°C)
Power-On Default
0x44
0x40
– Hysteresis. Up to 15°C of
MIN
MIN.