Datasheet ADT7461A (ON Semiconductor) - 8

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ADT7461A
The resulting DVBE waveforms are passed through a is performed by averaging the results of 16 measurement 65 kHz low-pass filter to remove noise and then to a cycles for low conversion rates. At rates of 16-, 32-, and chopper-stabilized amplifier. This amplifies and rectifies the 64-conversions/second, no digital averaging occurs. waveform to produce a dc voltage proportional to DVBE. Signal conditioning and measurement of the internal The ADC digitizes this voltage producing a temperature temperature sensor are performed in the same manner. measurement. To reduce the effects of noise, digital filtering 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 IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1000 pF MAX.
Figure 14. Input Signal Conditioning Temperature Measurement Results
used to measure the full temperature range of an external The results of the local and remote temperature diode, from −55°C to +150°C. measurements are stored in the local and remote temperature The extended temperature range is selected by setting value registers and compared with limits programmed into Bit 2 of the configuration register to 1. The temperature the local and remote high and low limit registers. range is 0°C to 127°C when Bit 2 equals 0. A valid result is The local temperature value is in Register 0x00 and has a available in the next measurement cycle after changing the resolution of 1°C. The external temperature value is stored temperature range. in two registers, with the upper byte in Register 0x01 and the In extended temperature mode, the upper and lower lower byte in Register 0x10. Only the two MSBs in the temperature that can be measured by the ADT7461A is external temperature low byte are used giving the external limited by the remote diode selection. The temperature temperature measurement a resolution of 0.25°C. Table 7 registers can have values from −64°C to +191°C. However, lists the data format for the external temperature low byte. most temperature sensing diodes have a maximum temperature range of −55°C to +150°C. Above +150°C, they
Table 7. EXTENDED TEMPERATURE RESOLUTION
may lose their semiconductor characteristics and
(REMOTE TEMPERATURE LOW BYTE)
approximate conductors instead. This results in a diode
Remote Temperature
short. In this case, a read of the temperature result register
Extended Resolution Low Byte
gives the last good temperature measurement. Therefore, 0.00°C 0 000 0000 the temperature measurement on the external channel may 0.25°C 0 100 0000 not be accurate for temperatures that are outside the operating range of the remote sensor. 0.50°C 1 000 0000 It should be noted that although both local and remote 0.75°C 1 100 0000 temperature measurements can be made while the part is in When reading the full external temperature value, read the extended temperature mode, the ADT7461A itself should LSB first. This causes the MSB to be locked (that is, the not be exposed to temperatures greater than those specified ADC does not write to it) until it is read. This feature ensures in the absolute maximum ratings section. Further, the device that the results read back from the two registers come from is only guaranteed to operate as specified at ambient the same measurement. temperatures from −40°C to +120°C.
Temperature Measurement Range Temperature Data Format
The temperature measurement range for both internal and The ADT7461A has two temperature data formats. When external measurements is, by default, 0°C to +127°C. the temperature measurement range is from 0°C to 127°C However, the ADT7461A can be operated using an (default), the temperature data format for both internal and extended temperature range. The extended measurement external temperature results is binary. When the measurement range is −64°C to +191°C. Therefore, the ADT7461A can be range is in extended mode, an offset binary data format is used
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