ADT7461ARM datasheet(10/24 Pages) AD

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ADT7461

×IN2×I

IBIAS

VDD

VOUT+

TO ADC

VOUT–

REMOTE

SENSING

TRANSISTOR

*CAPACITOR C1 IS OPTIONAL. IT SHOULD ONLY BE USED IN NOISY ENVIRONMENTS.

D+

D–

C1*

BIAS

DIODE

LOW-PASS FILTER

fC = 65kHz

Figure 14. Input Signal Conditioning

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 value is in Register 0×00 and has a

resolution of 1°C. The external temperature value is stored in

two registers, with the upper byte in Register 0×01 and the

lower byte in Register 0×10. Only the two MSBs in the external

temperature low byte are used. This gives the external tempera-

ture measurement a resolution of 0.25°C. T

shows the data

format for the external temperature low byte.

able 5

Table 5. 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 external temperature value, both the high

and low byte, the two registers should be read in succession.

Reading one register does not lock the other, so both should be

read before the next conversion finishes. In practice, there is

more than enough time to read both registers, as transactions

over the SMBus are significantly faster than a conversion time.

TEMPERATURE MEASUREMENT RANGE

The temperature measurement range for both internal and

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

the ADT7461 can be operated using an extended temperature

range. It can measure the full temperature range of an external

diode, from −55°C to +150°C. The user can switch between

these two temperature ranges by setting or clearing Bit 2 in

the configuration register. A valid result is available in the next

measurement cycle after changing the temperature range.

In extended temperature mode, the upper and lower tempera-

ture that can be measured by the ADT7461 is limited by the

remote diode selection. The temperature registers themselves

can have values from −64°C to +191°C. However, most tem-

perature sensing diodes have a maximum temperature range of

−55°C to +150°C.

It should be noted that while both local and remote temperature

measurements can be made while the part is in extended

temperature mode, the ADT7461 itself should not be exposed to

temperatures greater than those specified in the absolute maximum

ratings section. Further, the device is only guaranteed to operate as

specified at ambient temperatures from −40°C to +120°C.

TEMPERATURE DATA FORMAT

The ADT7461 has two temperature data formats. When the

temperature measurement range is from 0°C to +127°C (de-

fault), the temperature data format for both internal and exter-

nal temperature results is binary. When the measurement range

is in extended mode, an offset binary data format is used for

both internal and external results. Temperature values in the

offset binary data format are offset by +64. Examples of tem-

peratures in both data formats are shown in

Table 6

Rev. 0 | Page 10 of 24

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