Analog Devices dBCool ADT7476, Manual

Page: 66 / 72

ADT7476
Rev. B | Page 66 of 72
Table 43. THERM Limit Registers
1
Register Address R/W
2
Description Power-On Default
0x6A R/W Remote 1 THERM temperature limit 0x64 (100°C)
0x6B R/W Local THERM temperature limit 0x64 (100°C)
0x6C R/W Remote 2 THERM temperature limit 0x64 (100°C)
1
If any temperature measured exceeds its THERM limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail-safe mechanism incorporated to cool the
system in the event of a critical overtemperature. It also ensures some level of cooling in the event that software or hardware locks up. If set to 0x80, this feature is
disabled. The PWM output remains at 100% until the temperature drops below THERM limit – hysteresis. If the THERM pin is programmed as an output, exceeding
these limits by 0.25°C can cause the THERM pin to assert low as an output.
2 These registers become read-only when the Configuration Register 1 LOCK bit is set to 1. Any subsequent attempts to write to these registers fail.
Table 44. Temperature/T
MIN
Hysteresis Registers
1
Register Address Bit Name R/W
2
Description Power-On Default
0x6D R/W Remote 1 and Local Temperature hysteresis. 0x44
HYSL [3:0] Local temperature hysteresis. 0°C to 15°C of hysteresis can be
applied to the local temperature AFC control loops.
HYSR1 [7:4] Remote 1 temperature hysteresis. 0°C to 15°C of hysteresis can
be applied to the Remote 1 Temperature AFC control loops.
0x6E R/W Remote 2 temperature hysteresis. 0x40
HYSR2 [7:4] RemotetTemperature hysteresis. 0°C to 15°C of hysteresis can
be applied to the local temperature AFC control loops.
1 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
MIN
value, the fan remains running at PWM
MIN
duty cycle until the temperature = T
MIN
– hysteresis. Up to 15°C of hysteresis can 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 at 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
MIN
.
2
These registers become read-only when the Configuration Register 1 LOCK bit is set to 1. Any subsequent attempts to write to these registers fail.
Table 45. XNOR Tree Test Enable
Register Address Bit Name R/W 1 Description Power-On Default
0x6F R/W XNOR tree test enable. 0x00
XEN [0] 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 tree
test mode.
Reserved [7:1] Unused. Do not write to these bits.
1 This register becomes read-only when the Configuration Register 1 LOCK bit is set to 1. Any subsequent attempts to write to this register fail.
Table 46. Remote 1 Temperature Offset
Register Address Bit R/W
1
Description Power-On Default
0x70 [7:0] R/W Remote 1 temperature offset. 0x00
Allows a temperature offset to be applied automatically to the
Remote 1 temperature channel measurement. Bit 1 of
Configuration Register 5 (0x7C) determines the range and
resolution of this register.
1 This register becomes read-only when the Configuration Register 1 LOCK bit is set to 1. Any subsequent attempts to write to this register fail.
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