ADT7481 Просмотр технического описания (PDF) - Analog Devices

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ADT7481

Dual Channel Temperature Sensor and Over Temperature Alarm

Analog Devices 

ADT7481

TEMPERATURE MEASUREMENT RESULTS

The results of the local and remote temperature measurements

are stored in the local and remote temperature value registers

and are compared with limits programmed into the local and

remote high and low limit registers.

The local temperature measurement is an 8-bit measurement

with 1°C resolution. The remote temperature measurements are

10-bit measurements, with the 8 MSBs stored in one register

and the 2 LSBs stored in another register. Table 5 is a list of the

temperature measurement registers.

Table 5. Register Address for the Temperature Values

Temperature

Register Address, Register Address,

Channel

MSBs

LSBs

Local

0x00

N/A

Remote 1

0x01

0x10 (2 MSBs)

Remote 2

0x30

0x33 (2 MSBs)

If Bit 3 of the Configuration 1 register is set to 1, then the

Remote 2 temperature values can be read from the following

register addresses:

Remote 2, MSBs = 0x01

Remote 2, LSBs = 0x10

The above is true only when Bit 3 of the Configuration 1 register

is set. To read the Remote 1 temperatures, this bit needs to be

switched back to 0.

Only the two MSBs in the remote temperature low byte are

used. This gives the remote temperature measurement a

resolution of 0.25°C. Table 6 shows the data format for the

remote temperature low byte.

Table 6. Extended Temperature Resolution

(Remote Temperature Low Byte)

Extended Resolution Remote Temperature Low Byte

0.00°C

0 000 0000

0.25°C

0 100 0000

0.50°C

1 000 0000

0.75°C

1 100 0000

When reading the full remote temperature value, including both

the high and low byte, the two registers should be read LSB first

and then the MSB. This is because reading the LSB will cause the

MSB to be locked until it is read. This is to guarantee that the two

values read are derived from the same temperature measurement.

The MSB register updates only after it has been read. The MSB

will not lock if a SMBus repeat start is used between reading the

two registers. There needs to be a stop between reading the LSB

and MSB.

If the LSB register is read but not the MSB register, then fail-safe

protection is provided by the THERM and ALERT signals

which update with the latest temperature measurements rather

than the register values.

TEMPERATURE MEASUREMENT RANGE

The temperature measurement range for both local and remote

measurements is, by default, 0°C to +127°C. However, the

ADT7481 can be operated using an extended temperature range.

The temperature range in the extended mode is −64°C to +191°C.

The user can switch between these two temperature ranges by

setting or clearing Bit 2 in the Configuration 1 register. A valid

result is available in the next measurement cycle after changing

the temperature range.

Bit 2 Configuration Register 2 = 0 = 0°C to +127°C = default

Bit 2 Configuration Register 2 = 1 = −64°C to +191°C

In extended temperature mode, the upper and lower temperatures

that can be measured by the ADT7481 are limited by the remote

diode selection. While the temperature registers can have values

from −64°C to +191°C, most temperature sensing diodes have a

maximum temperature range of −55°C to +150°C.

Note that while both local and remote temperature measurements

can be made while the part is in extended temperature mode,

the ADT7481 should not be exposed to temperatures greater

than those specified in the Absolute section. Furthermore, the

device is only guaranteed to operate as specified at ambient

temperatures from −40°C to +120°C.

TEMPERATURE DATA FORMAT

The ADT7481 has two temperature data formats. When the

temperature measurement range is from 0°C to +127°C

(default), the temperature data format is binary for both local

and remote temperature results. See the Temperature Measurement

Range section for information on how to switch between the

two data formats.

When the measurement range is in extended mode, an offset

binary data format is used for both local and remote results.

Temperature values in the offset binary data format are offset by

+64. Examples of temperatures in both data formats are shown

in Table 7.

Rev. 0 | Page 10 of 24

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