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Technical Description
The regulators have got an enable input, which is used to power the phone on/off.
The minimum voltage for turning the regulators on is 2.0V, and the maximum for
turning them off is 0.18V.
Reset
The digital voltage VDIG is monitored by a low voltage detector in ANTON. While
the phone is operating, and if VDIG drops below 3.35V (typical), ANTON's LVN
open-drain output will set GUSTAV's reset input (MRN) low, causing the processor
to reset. Upon power-up, an RC filter holds GUSTAV's reset input low for the
required 20 ms delay.
On/Off Control
The phone may be powered on by either pressing the ON/OFF/END key, or by
applying 7.0V-10.0V at DCIO.
When the ON/OFF/END key is pressed for at least 200 ms, this key powers on the
phone by connecting the battery voltage to the enable inputs of the regulators
through a diode. The processor then comes out of reset and latches the enable inputs
of the regulators.
Chargers and accessories power on the phone by applying 7.0V-10.0V at DCIO.
The voltage difference between DCIO and the battery voltage turns on a transistor
connected to the enable inputs of the regulators. As with the ON/OFF/END key, the
DCIO voltage must be present for at least 200 ms in order to power on the phone.
If no charger is connected, the phone is powered-off by pressing and then releasing
the ON/OFF/END key. Pressing the ON/OFF/END key generates an interrupt to
GUSTAV via a transistor. GUSTAV then tries to disable the regulators but these will
stay on until the ON/OFF/END key is released. If a charger is connected, the phone
will stay on until the processor detects that the charger has been removed (no cur-
rent from charger to phone). The phone cannot turn itself off as long as a charger is
connected.
Charging Circuitry
The phone software controls charging by turning a FET switch on/off, based on bat-
tery voltage and charging current through a 0.1Ω resistor. Chargers are designed to
have an open-circuit voltage less than 10V, and supply an average current of approx-
imately 700mA when connected to a battery through the FET switch. A resistor
allows a dead battery to become trickle charged high enough for the phone to turn
on. MIA provides charge switch control and analog outputs corresponding to
charger current and battery voltage. These outputs are connected to BERTINDY's
A/D inputs. GUSTAV turns on the charge switch using a current control output port,
which is connected to an input of MIA. If the battery voltage is less than 8.0V, the
current control port controls the on/off state of the FET switch. If the battery voltage
is greater than 8.0V, MIA keeps the charge switch off regardless of the state of the
current control port.
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