Specifications

AC65/AC75 Hardware Interface Description
3.3 Power-Up / Power-Down Scenarios
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AC65_AC75_HD_v01.002 Page 39 of 117 2006-10-30
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3.3.4.4 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 suffi-
cient 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 shut-
down 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.
3.3.4.5 Undervoltage Shutdown if no Battery NTC is Present
The undervoltage protection is also effective in applications, where no NTC connects to the BATT_TEMP termi-
nal. Thus, you can take advantage of this feature even though the application handles the charging process or
AC65/AC75 is fed by a fixed supply voltage. All you need to do is executing the write command AT^SBC=<cur-
rent> 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.
3.3.4.6 Overvoltage Shutdown
The overvoltage shutdown threshold is 100mV above the maximum supply voltage V
BATT+
specified in Table 27.
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 AC65/AC75 components are directly linked to BATT+ and, therefore, the supply volt-
age remains applied at major parts of AC65/AC75, even if the module is switched off. Especially the power ampli-
fier is very sensitive to high voltage and might even be destroyed.