Charging Process - Wavecom GR64 GSM/GPRS Integrator's Manual

During microprocessor supervised mode, the GR64 takes a current-limited voltage
source at the CHG_IN pin to implement constant-current charging of a single Li-Ion
cell connected to the VCC pins.
Figure 12: Typical application for pulse charging a battery
5.7.1

Charging Process

Figure 12 shows a typical battery charging implementation. The voltage source must
be current limited (500 mA max).
external fault conditions from draining the battery.
should be placed close to the CHG_IN pin.
In the application shown, a conditioning phase slowly raises the voltage of a deeply
discharged battery cell to a level suitable for fast-charging. After cell conditioning is
complete, the microprocessor uses the GR64'S ADC converter to monitor the cell's
status and uses the power management block to control the charge-FET.
A charge request is initiated when an external voltage source (CPS) is applied to the
CHG_IN pin. However, before this request is passed to the microprocessor, CHG_IN is
verified to be greater than VCC by 150 mV, and at least 3.7 V. If the latter criterion is
not met, the Wireless CPU limits charging to the conditioning phase. If the former
criterion is not met, the charge request is ignored and all charging is disabled. If the
CHG_IN voltage exceeds the upper limit of 6.3 V it will be detected by the Wireless
CPU, but charging is not inhibited.
normal operating range of the device, so the software will not initiate charging if
CHG_IN > 6.3 V is detected.
The delta between CHG_IN and VCC is continuously monitored; however, the valid to
invalid detection has a delay of 46 ms. When CHG_IN exceeds VCC by 150 mV, it is
considered to be at a valid relative level. It is considered to have an invalid relative
GR64 Integrators Manual
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A reverse current protection diode prevents
In this case, however, CHG_IN is outside the
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A small (typ 10µF) capacitor