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ADT7481ARMZ-1RL Datasheet(PDF) 8 Page - ON Semiconductor |
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ADT7481ARMZ-1RL Datasheet(HTML) 8 Page - ON Semiconductor |
8 / 20 page ADT7481 http://onsemi.com 8 Table 1. Register Address for the Temperature Values Temperature Channel Register Address, MSBs Register Address, LSBs Local 0x00 N/A Remote 1 0x01 0x10 (2 MSBs) Remote 2 0x30 0x33 (2 MSBs) If Bit 3 of the Configuration 1 register is set to 1, then the Remote 2 temperature values can be read from the following register addresses: Remote 2, MSBs = 0x01 Remote 2, LSBs = 0x10 The above is true only when Bit 3 of the Configuration 1 register is set. To read the Remote 1 temperatures, this bit needs to be switched back to 0. Only the two MSBs in the remote temperature low byte are used. This gives the remote temperature measurement a resolution of 0.25 °C. Table 2 shows the data format for the remote temperature low byte. Table 2. 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 remote temperature value, including both the high and low byte, the two registers should be read LSB first and then the MSB. This is because reading the LSB will cause the MSB to be locked until it is read. This is to guarantee that the two values read are derived from the same temperature measurement. The MSB register updates only after it has been read. The MSB will not lock if a SMBus repeat start is used between reading the two registers. There needs to be a stop between reading the LSB and MSB. If the LSB register is read but not the MSB register, then fail−safe protection is provided by the THERM and ALERT signals which update with the latest temperature measurements rather than the register values. Temperature Measurement Range The temperature measurement range for both local and remote measurements is, by default, 0 °C to +127°C. However, the ADT7481 can be operated using an extended temperature range. The temperature range in the extended mode is −64 °C to +191°C. The user can switch between these two temperature ranges by setting or clearing Bit 2 in the Configuration 1 register. A valid result is available in the next measurement cycle after changing the temperature range. Bit 2 Configuration Register 2 = 0 = 0 °C to +127°C = default Bit 2 Configuration Register 2 = 1 = −64 °C to +191°C In extended temperature mode, the upper and lower temperatures that can be measured by the ADT7481 are limited by the remote diode selection. While the temperature registers can have values from −64 °C to +191°C, most temperature sensing diodes have a maximum temperature range of −55 °C to +150°C. Note that while both local and remote temperature measurements can be made while the part is in extended temperature mode, the ADT7481 should not be exposed to temperatures greater than those specified in the Absolute section. Furthermore, the device is only guaranteed to operate as specified at ambient temperatures from −40 °C to +120°C. Temperature Data Format The ADT7481 has two temperature data formats. When the temperature measurement range is from 0 °C to +127°C (default), the temperature data format is binary for both local and remote temperature results. See the Temperature Measurement Range section for information on how to switch between the two data formats. When the measurement range is in extended mode, an offset binary data format is used for both local and remote results. Temperature values in the offset binary data format are offset by +64. Examples of temperatures in both data formats are shown in Table 3. Table 3. Temperature Data Format (Local and Remote Temperature High Byte) Temperature Binary Offset Binary (Note 1) −55°C 0 000 0000 (Note 2) 0 000 1001 110°C 0 000 0000 0 100 0000 +1°C 0 000 0001 0 100 0001 +10°C 0 000 1010 0 100 1010 +25°C 0 001 1001 0 101 1001 +50°C 0 011 0010 0 111 0010 +75°C 0 100 1011 1 000 1011 +100°C 0 110 0100 1 010 0100 +125°C 0 111 1101 1 011 1101 +127°C 0 111 1111 1 011 1111 +150°C 0 111 1111 (Note 3) 1 101 0110 1. Offset binary scale temperature values are offset by +64. 2. Binary scale temperature measurement returns 0 for all temperatures <0°C. 3. Binary scale temperature measurement returns 127 for all temperatures >127°C. The user may switch between measurement ranges at any time. Switching the range will also switch the data format. The next temperature result following the switching will be reported back to the register in the new format. However, the contents of the limit registers will not change. It is up to the user to ensure that when the data format changes, the limit registers are reprogrammed as necessary. More information on this can be found in the Limit Registers section. |
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