User's Manual

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Figure 5: Example of how to make a power on/off button using latch feature of the internal
regulators
In Figure 5 the internal regulators are latched on at the rising edge, i.e when pressing SW1. One of the
PIOs is configured to power hold thus keeping the external regulator on until shut down by pressing
SW1 again.
5.3 Battery Charger
The battery charger is a constant current / constant voltage charger circuit, and is suitable for lithium
ion/polymer batteries only. It shares a connection to the battery terminal, VDD_BAT, with the switch-
mode regulator. The charger is initially calibrated by Bluegiga Technologies to have V
float
= 4.2 V.
The constant current level can be varied to allow charging of different capacity batteries. WT32 allows a
number of different currents to be used in the battery charger hardware. Values written to PS key
0x039b CHARGER_CURRRENT in the range 1..15 specify the charger current from 40..135mA in even
steps. Values outside the valid 0..15 range result in no change to the charging current. The default
charging current (Key = 0) is nominally
40mA. Setting 0 is interpreted as “no-change” so will be ignored
The charger enters various states of operation as it charges a battery. These are shown below:
 Off: entered when the charger is disconnected.
 Trickle Charge: entered when the battery voltage is below 2.9V.
 Fast Charge - Constant Current: entered when the battery voltage is above 2.9V.