The LM75A uses the on-chip band gap sensor to measure the device temperature with the resolution of 0.125 °C and stores the 11-bit 2's complement digital data, resulted from 11-bit A-to-D conversion, into the device Temp register. This is a figure of block diagram for the circuit of digital temperature sensor;
The device can be set to operate in either mode: normal or shutdown. In normal operation mode, the temp-to-digital conversion is executed every 100 ms and the Temp register is updated at the end of each conversion. In shutdown mode, the device becomes idle, data conversion is disabled and the Temp register holds the latest result; however, the device I2C-bus interface is still active and register write/read operation can be performed. The device operation mode is controllable by programming bit B0 of the configuration register. The temperature conversion is initiated when the device is powered-up or put back into normal mode from shutdown.
In addition, at the end of each conversion in normal mode, the temperature data (or Temp) in the Temp register is automatically compared with the over-temperature shutdown threshold data (or Tos) stored in the Tos register, and the hysteresis data (or Thyst) stored in the Thyst register, in order to set the state of the device OS output accordingly. The device Tos and Thyst registers are write/read capable, and both operate with 9-bit 2's complement digital data. To match with this 9-bit operation, the Temp register uses only the 9 MSB bits of its 11-bit data for the comparison.
[Schematic circuit source: NXP Semiconductor Notes]
0 comments:
Post a Comment