> 3.3.4 | Automatic Shutdown

> Automatic shutdown takes effect if:

> • | the TC65 board is exceeding the critical limits of overtemperature or undertemperature

> • | the battery is exceeding the critical limits of overtemperature or undertemperature

> • | undervoltage or overvoltage is detected

> See Charge-only mode described in Section 3.5.7 for exceptions.
> The automatic shutdown procedure is equivalent to the Power-down initiated with the AT^SMSO command, i.e. TC65 logs off from the network and the software enters a secure state avoiding loss of data.
> Alert messages transmitted before the device switches off are implemented as Unsolicited Result Codes (URCs). The presentation of these URCs can be enabled or disabled with the two AT commands AT^SBC and AT^SCTM. The URC presentation mode varies with the condition, please see Section 3.3.4.1 to Section 3.3.4.5 for details. For further instructions on AT commands refer to [1].

> 3.3.4.1 | Thermal Shutdown

> The board temperature is constantly monitored by an internal NTC resistor located on the PCB. The NTC that detects the battery temperature must be part of the battery pack circuit as described in Section 3.5.3 The values detected by either NTC resistor are measured directly on the board or the battery and therefore, are not fully identical with the ambient temperature.
> Each time the board or battery temperature goes out of range or back to normal, TC65 instantly displays an alert (if enabled).

> • | URCs indicating the level "1" or "-1" allow the user to take appropriate precautions, such as protecting the module from exposure to extreme conditions. The presentation of the URCs depends on the settings selected with the AT^SCTM write command:

> AT^SCTM=1: Presentation of URCs is always enabled.
> AT^SCTM=0 (default): Presentation of URCs is enabled for 15 seconds time after start-up of TC65. After 15 seconds operation, the presentation will be disabled, i.e. no alert messages can be generated.

> • | URCs indicating the level "2" or "-2" are instantly followed by an orderly shutdown, except in cases described in Section 3.3.4.2. The presentation of these URCs is always enabled, i.e. they will be output even though the factory setting AT^SCTM=0 was never changed. The maximum temperature ratings are stated in Section 5.2. Refer to Table 9 for the associated URCs.

> Table 9: | Temperature dependent behavior

> Sending temperature alert (15s after TC65 start-up, otherwise only if URC presentation enabled)
> ^SCTM_A: 1 | Caution: Battery close to overtemperature limit.
> ^SCTM_B: 1 | Caution: Board close to overtemperature limit.
> ^SCTM_A: -1 | Caution: Battery close to undertemperature limit.
> ^SCTM_B: -1 | Caution: Board close to undertemperature limit.
> ^SCTM_A: 0 | Battery back to uncritical temperature range.
> ^SCTM_B: 0 | Board back to uncritical temperature range.
> Automatic shutdown (URC appears no matter whether or not presentation was enabled)
> ^SCTM_A: 2 | Alert: Battery equal or beyond overtemperature limit. TC65 switches off.
> ^SCTM_B: 2 | Alert: Board equal or beyond overtemperature limit. TC65 switches off.
> ^SCTM_A: -2 | Alert: Battery equal or below undertemperature limit. TC65 switches off.
> ^SCTM_B: -2 | Alert: Board equal or below undertemperature limit. TC65 switches off.

> 3.3.4.2 | Temperature Control during Emergency call

> If the temperature limit is exceeded while an emergency call is in progress the engine continues to measure the temperature, but deactivates the shutdown functionality. If the temperature is still out of range when the call ends, the module switches off immediately (without another alert message).

> 3.3.4.3 | Undervoltage Shutdown if Battery NTC is Present

> In applications where the module’s charging technique is used and an NTC is connected to the BATT_TEMP terminal, the software constantly monitors the applied voltage. If the measured battery voltage is no more sufficient to set up a call the following URC will be presented:
> ^SBC: Undervoltage.
> The message will be reported, for example, when you attempt to make a call while the voltage is close to the shutdown threshold of 3.2V and further power loss is caused during the transmit burst. In IDLE mode, the shutdown threshold is the sum of the module’s minimum supply voltage (3.2V) and the value of the maximum voltage drop resulting from earlier calls. This means that in IDLE mode the actual shutdown threshold may be higher than 3.2V. Therefore, to properly calculate the actual shutdown threshold application manufacturers are advised to measure the maximum voltage drops that may occur during transmit bursts.
> To remind you that the battery needs to be charged soon, the URC appears several times before the module switches off.
> This type of URC does not need to be activated by the user. It will be output automatically when fault conditions occur.

> 3.3.4.4 | Undervoltage Shutdown if no Battery NTC is Present

> The undervoltage protection is also effective in applications, where no NTC connects to the BATT_TEMP terminal. Thus, you can take advantage of this feature even though the application handles the charging process or TC65 is fed by a fixed supply voltage. All you need to do is executing the write command AT^SBC=<current> which automatically enables the presentation of URCs. You do not need to specify <current>.
> Whenever the supply voltage falls below the value of 3.2V the URC
> ^SBC: Undervoltage
> appears several times before the module switches off.
> This type of URC does not need to be activated by the user. It will be output automatically when fault conditions occur.

> 3.3.4.5 | Overvoltage Shutdown

> The overvoltage shutdown threshold is 100mV above the maximum supply voltage V BATT+ specified in Figure 28.
> When the supply voltage approaches the overvoltage shutdown threshold the module will send the URC
> ^SBC: Overvoltage warning.
> This alert is sent once.
> When the overvoltage shutdown threshold is exceeded the module will send the URC
> ^SBC: Overvoltage shutdown
> before it shuts down cleanly.
> This type of URC does not need to be activated by the user. It will be output automatically when fault conditions occur.
> Keep in mind that several TC65 components are directly linked to BATT+ and, therefore, the supply voltage remains applied at major parts of TC65, even if the module is switched off. Especially the power amplifier is very sensitive to high voltage and might even be destroyed.