Datasheet ADT7461 (ON Semiconductor) - 8

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ADT7461
VDD I N1 × I N2 × I IBIAS D+ VOUT+ REMOTE C1* To ADC SENSING TRANSISTOR D− VOUT− BIAS LOW-PASS FILTER DIODE fC = 65 kHz *CAPACITOR C1 IS OPTIONAL. IT SHOULD ONLY BE USED IN NOISY ENVIRONMENTS.
Figure 15. Input Signal Conditioning Temperature Measurement Results
of an external diode, from −55°C to +150°C. The user can The results of the local and remote temperature switch between these two temperature ranges by setting or measurements are stored in the local and remote temperature clearing Bit 2 in the configuration register. A valid result is value registers and are compared with limits programmed available in the next measurement cycle after changing the into the local and remote high and low limit registers. temperature range. The local temperature value is in Register 0x00 and has a In extended temperature mode, the upper and lower resolution of 1°C. The external temperature value is stored in temperature that can be measured by the ADT7461 is two registers, with the upper byte in Register 0x01 and the limited by the remote diode selection. The temperature lower byte in Register 0x10. Only the two MSBs in the external registers themselves can have values from −64°C to +191°C. temperature low byte are used. This gives the external However, most temperature sensing diodes have a temperature measurement a resolution of 0.25°C. Table 6 maximum temperature range of −55°C to +150°C. shows the data format for the external temperature low byte. Above 150°C, they may lose their semiconductor characteristics and approximate conductors instead. This
Table 6. EXTENDED TEMPERATURE RESOLUTION
results in a diode short. In this case, a read of the temperature
(REMOTE TEMPERATURE LOW BYTE)
result register gives the last good temperature measurement.
Remote Temperature
The user should be aware that the temperature measurement
Extended Resolution Low Byte
on the external channel may not be accurate for temperatures 0.00°C 0 000 0000 that are outside the operating range of the remote sensor. 0.25°C 0 100 0000 While both local and remote temperature measurements can be made while the part is in extended temperature mode, 0.50°C 1 000 0000 the ADT7461 itself should not be exposed to temperatures 0.75°C 1 100 0000 greater than those specified in the Absolute Maximum When reading the full external temperature value, both the Ratings section. Also, the device is guaranteed to operate only high and low byte, the two registers should be read in as specified at ambient temperatures from −40°C to +120°C. succession. Reading one register does not lock the other, so
Temperature Data Format
both should be read before the next conversion finishes. In The ADT7461 has two temperature data formats. When the practice, there is more than enough time to read both temperature measurement range is from 0°C to +127°C registers, as transactions over the SMBus are significantly (default), the temperature data format for both internal and faster than a conversion time. external temperature results is binary. When the measurement
Temperature Measurement Range
range is in extended mode, an offset binary data format is used The temperature measurement range for both internal and for both internal and external results. Temperature values in external measurements is, by default, 0°C to +127°C. the offset binary data format are offset by 64°C. Examples of However, the ADT7461 can be operated using an extended temperatures in both data formats are shown in Table 7. temperature range. It can measure the full temperature range
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