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ADT7461AARMZ-REEL

±1°C Temperature Monitor with Series Resistance Cancellation

Analog Devices 

VDD

I

N1 × I N2 × I

IBIAS

ADT7461A

REMOTE

SENSING

TRANSISTOR

D+

C11

D–

BIAS

DIODE

LPF

fC = 65kHz

VOUT+

TO ADC

VOUT–

1CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1000pF MAX.

Figure 15. 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 compared with limits programmed into the local and

remote high and low limit registers.

The local temperature value is in Register 0x00 and has a

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

two registers, with the upper byte in Register 0x01 and the

lower byte in Register 0x10. Only the two MSBs in the external

temperature low byte are used giving the external temperature

measurement a resolution of 0.25°C. Table 7 lists the data

format for the external temperature low byte.

Table 7. 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, read the LSB

first. This causes the MSB to be locked (that is, the ADC does

not write to it) until it is read. This feature ensures that the

results read back from the two registers come from the same

measurement.

TEMPERATURE MEASUREMENT RANGE

The temperature measurement range for both internal and

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

the ADT7461A can be operated using an extended temperature

range. The extended measurement range is −64°C to +191°C.

Therefore, the ADT7461A can be used to measure the full

temperature range of an external diode, from −55°C to +150°C.

The extended temperature range is selected by setting Bit 2 of

the configuration register to 1. The temperature range is 0°C

to 127°C when Bit 2 equals 0. A valid result is available in the

next measurement cycle after changing the temperature range.

In extended temperature mode, the upper and lower temperature

that can be measured by the ADT7461A is limited by the

remote diode selection. The temperature registers can have

values from −64°C to +191°C. However, most temperature

sensing diodes have a maximum temperature range of −55°C to

+150°C. Above +150°C, they may lose their semiconductor

characteristics and approximate conductors instead. This results

in a diode short. In this case, a read of the temperature result

register gives the last good temperature measurement. Therefore,

the temperature measurement on the external channel may not

be accurate for temperatures that are outside the operating range

of the remote sensor.

It should be noted that although both local and remote temperature

measurements can be made while the part is in extended

temperature mode, the ADT7461A 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 ADT7461A has two temperature data formats. When the

temperature measurement range is from 0°C to 127°C (default),

the temperature data format for both internal and external

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 are offset by

64°C in the offset binary data format. Examples of temperatures

in both data formats are shown in Table 8.

Rev. A | Page 11 of 24

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