Undervoltage Shutdown If No Battery Ntc Is Present; Overvoltage Shutdown - Siemens AC75 Hardware Interface Description

AC75 Hardware Interface Description
Strictly confidential / Preliminary
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.
To enable or disable the URC use the AT^SBC command. The URC will be enabled when
you enter the write command and specify the current consumption of your host application.
Step by step instructions are provided in [1].
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 terminal. Thus, you can take advantage of this feature even though the
application handles the charging process or AC75 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.
3.3.4.6

Overvoltage Shutdown

The overvoltage shutdown threshold is 100mV above the maximum supply voltage V
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.
Keep in mind that several AC75 components are directly linked to BATT+ and, therefore, the
supply voltage remains applied at major parts of AC75, even if the module is switched off.
Especially the power amplifier is very sensitive to high voltage and might even be destroyed.
AC75_HD_V00.202 Page 39 of 120
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BATT+
27.04.2006