nRF9160 has a built-in thermal protection mechanism to prevent RF Power Amplifier (PA) from breaking and the LTE modem from operating beyond the specified temperature range.
When the internal temperature sensor in nRF9160 measures a case temperature of approximately 90°C, the LTE modem and Global Positioning System (GPS) receiver are deactivated to minimize the internal generation of heat and to protect RF PA. The application can monitor case temperature using the %XTEMP AT command. When %XTEMP indicates that the case temperature has dropped below the critical level, the application can reactivate the LTE modem with the +CFUN AT command.
For more information on thermal protection, see Internal temperature %XTEMP in nRF9160 AT Commands Reference Guide.