Rainbow Electronics LM85 - Manual (Page 22)

Functional Description
(Continued)
4.19 Registers 6A-6Ch: Absolute Temperature Limit
Register
Address
Read/
Write
Register
Name
Bit 7
(MSB)
Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
(LSB)
Default
Value
Lock?
6Ah R/W Zone1 Absolute Temp Limit 7 6 5 4 3 2 1 0 64h U
6Bh R/W Zone2 Absolute Temp Limit 7 6 5 4 3 2 1 0 64h U
6Ch R/W Zone3 Absolute Temp Limit 7 6 5 4 3 2 1 0 64h U
For the LM85B in the Auto Fan mode, if a zone exceeds the temperature set in the Absolute Temperature Limit register, all of the
PWM outputs will incresase its duty cycle to 100%. This is a safety feature that attempts to cool the system if there is a potentially
catastrophic thermal event. If set to 80h (-128˚C), the feature is disabled. Default=100˚C=64h
For the LM85C in the Auto Fan mode, if a zone exceeds the temperature set in the Absolute Temperature Limit register, only the
PWM output associated with the Absolute Temperature Limit will go to 100%.
These registers become Read Only when the Ready/Lock/Start/Override register Lock bit is set. Any further attempts to write to
these registers shall have no effect. After power up the default values are used whenever the Ready/Lock/Start/Override register
Start bit is cleared even though modifications to these registers are possible.
TABLE 11. Absolute Limit vs Register Setting
Temperature Reading (Decimal) Reading (Hex)
−127˚C −127 81h
.
.
.
.
.
.
.
.
.
−50˚C −50 CEh
.
.
.
.
.
.
.
.
.
0˚C 0 00h
.
.
.
.
.
.
.
.
.
50˚C 50 32h
.
.
.
.
.
.
.
.
.
127˚C 127 7Fh
4.20 Registers 6D-6Eh: Zone Hysteresis Registers
Register
Address
Read/
Write
Register
Name
Bit 7
(MSB)
Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
(LSB)
Default
Value
Lock?
6Dh R/W Zone1 and Zone2 Hysteresis H1-3 H1-2 H1-1 H1-0 H2-3 H2-2 H2-1 H2-0 44h U
6Eh R/W Zone3 Hysteresis H3-3 H3-2 H3-1 H3-0 RES RES RES RES 40h U
If the temperature is above Fan Temp Limit, then drops below Fan Temp Limit, the following will occur:
– The fan will remain on, at Fan PWM Minimum, until the temperature goes a certain amount below Fan Temp Limit.
– The Hysteresis registers control this amount. See below table for details.
These registers become Read Only when the Ready/Lock/Start/Override register Lock bit is set. Any further attempts to write to
thses registers shall have no effect. After power up the default value is used whenever the Ready/Lock/Start/Override register
Start bit is cleared even though modifications to this register are possible.
TABLE 12. Hysteresis Settings
Setting HYSTERESIS
0h 0˚C
LM85
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