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

654321

0

64h

U

6Bh

R/W

Zone2 Absolute Temp Limit

7

654321

0

64h

U

6Ch

R/W

Zone3 Absolute Temp Limit

7

654321

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

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