ADS1118 temperature conversion time

Naoki-san,

Thank you for your query and sorry for the delay. 

The Temperature sensor mode is enabled by setting bit TS_MODE = 1 in the Config Register.

If the device is in continuous conversion mode, the ADC is configured to Temperature sensor mode after the current conversion is completed, and does not change immediately after changing the register. After we send a command to set the ADC in Temperature sensor mode, the worst case time required to receive an output with the new configuration will be 2*(1/data rate). Imagine that you send the command to enable the TS_MODE bit right after the converter just started a conversion. It would take all the time to complete the ongoing conversion and then set the TS_MODE = 1 and finally complete the new conversion with the new setting. Also, remember that the internal oscillator variation spec +/-10% and hence the output data rate will too vary by the same amount. Hence, the maximum time required to receive an output data once we change any setting in Config Register is 2*(1/(0.9*data rate)).

Giving you an example, for data rate of 64 SPS, the worst case time required to read from the temperature sensor  = 2*(1/(0.9*64)

 = 34.72 ms

 ≈ 35 ms

If we need to ensure the first conversion data after a the TS_MODE bit is enabled has the temperature sensor reading, it might be more efficient to run the device in single-shot mode. Please note that if you do run the device in single-shot mode, there's an extra 20 us required for the device to power up and start the conversion.

Please let me know if you have any further questions.

Thanks,

Krunal