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NCT72DMNR2G Datasheet(PDF) 8 Page - ON Semiconductor |
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NCT72DMNR2G Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 21 page NCT72 http://onsemi.com 8 Figure 14. Input Signal Conditioning LOW-PASS FILTER fC = 65 kHz REMOTE SENSING TRANSISTOR BIAS DIODE D+ D− VDD IBIAS I N1 I VOUT+ VOUT− To ADC N2 I C1* *CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1,000 pF MAX. 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 1C. 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 0.25C. Table 6 lists the data format for the external temperature low byte. Table 6. EXTENDED TEMPERATURE RESOLUTION (REMOTE TEMPERATURE LOW BYTE) Extended Resolution Remote Temperature Low Byte 0.00C 0 000 0000 0.25C 0 100 0000 0.50C 1 000 0000 0.75C 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, 0C to +127C. However, the NCT72 can be operated using an extended temperature range. The extended measurement range is −64C to +191C. Therefore, the NCT72 can be used to measure the full temperature range of an external diode, from −55C to +150C. The extended temperature range is selected by setting Bit 2 of the configuration register to 1. The temperature range is 0C to 127C 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 NCT72 is limited by the remote diode selection. The temperature registers can have values from −64C to +191C. However, most temperature sensing diodes have a maximum temperature range of −55C to +150C. Above +150C, 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 NCT72 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 −40C to +120C. Temperature Data Format The NCT72 has two temperature data formats. When the temperature measurement range is from 0C to 127C (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 64C in the offset binary data format. Examples of temperatures in both data formats are shown in Table 7. |
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