ADT7462ACPZ-R7 datasheet(20/81 Pages) ONSEMI

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ADT7462

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When reading the full temperature value, the LSB should

be read first and then the MSB. Reading the LSBs causes the

current MSBs to be frozen until they are read. Reading the

MSBs only does not cause any register to be locked. This is

useful when a temperature reading with 1

°C resolution is

required.

Series Resistance Cancellation

Parasitic resistance in series with the remote diode D+ and

D− inputs can be caused by a variety of factors, including

PCB track resistance and track length. This series resistance

appears as a temperature offset in the remote sensor’s

temperature measurement. This error typically causes a

0.8

°C offset per ohm of parasitic resistance in series with the

remote diode.

The ADT7462 automatically cancels out the effect of this

series resistance on the temperature reading, giving a more

accurate result, without the need for user characterization of

this resistance. The ADT7462 is designed to automatically

cancel typically up to 2 k

W of resistance. By using an

advanced temperature measurement method, the process is

transparent to the user. This feature also allows an RCR filter

to be added to the sensor path, allowing the part to be used

accurately in noisy environments.

Temperature Limits

Each temperature measurement channel has a high and

low temperature limit associated with it. The temperature

measurements are compared with these limits, and the

results of these comparisons are stored in status registers. A

Logic 0 indicates an in−limit comparison, and a Logic 1

indicates an out−of−limit comparison. The ADT7462 can

generate an ALERT, if configured to do so, after a status bit

is set. For more information on the status registers and

ALERT, see the Status and Mask Registers ALERT section.

Each temperature channel also has a THERM1 and a

THERM2 temperature limit associated with it. When these

temperature limits are exceeded, the corresponding

THERM pin is asserted low (if THERM is configured as an

output), and the fans are boosted to full speed (if the boost

bit is set). Table 10 shows a complete list of all the

temperature limits and their default values.

Table 10. Temperature Limit Registers

Temperature Value

Address

Default

Local Low Temperature Limit

0x44

0x40

Remote 1 Low Temperature Limit

0x45

0x40

Remote 2 Low Temperature Limit

0x46

0x40

Remote 3 Low Temperature Limit

0x47

0x40

Local High Temperature Limit

0x48

0x95

Remote 1 High Temperature Limit

0x49

0x95

Remote 2 High Temperature Limit

0x4A

0x95

Remote 3 High Temperature Limit

0x4B

0x95

Local THERM1 Temperature Limit

0x4C

0xA4

Remote 1 THERM1 Temperature Limit

0x4D

0xA4

Remote 2 THERM1 Temperature Limit

0x4E

0xA4

Remote 3 THERM1 Temperature Limit

0x4F

0xA4

Local THERM2 Temperature Limit

0x50

0xA4

Remote 1 THERM2 Temperature Limit

0x51

0xA4

Remote 2 THERM2 Temperature Limit

0x52

0xA4

Remote 3 THERM2 Temperature Limit

0x53

0xA4

Offset Registers

The ADT7462 has temperature offset registers at Register

0x56 to Register 0x59 for the local, Remote 1, Remote 2, and

Remote 3 temperature channels. By doing a one−time

calibration of the system, the user can determine the offset

caused by system board noise and cancel it using the offset

registers. The offset registers automatically add a twos

complement, 8−bit

reading to every temperature

measurement. The LSBs add 0.5

°C offset to the temperature

reading so the 8−bit register effectively allows temperature

offsets of up to

±64°C with a resolution of 0.5°C. This ensures

that the readings in the temperature measurement registers are

as accurate as possible.

Temperature Offset Registers

°C default)

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