User's Manual

LZT 123 1836 43
A charge request is initiated when an external voltage source 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 criteria is not met,
the module limits charging to the conditioning phase. If the former criteria 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 module, but charging is not
inhibited. In this case, however, CHG_IN is outside the 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
level if it subsequently falls below VCC by 50 mV. If the relative voltage of CHG_IN
goes invalid and remains invalid for the duration of the detection delay, charging is
terminated.
As a safety precaution, the battery cell voltage must be at least 2.5 V before fast-
charge is allowed to take place. If the battery cell voltage is less than 2.5 V, it is
considered either deeply discharged or shorted. To protect a Li-ion cell from the
damage that may occur if it is fast-charged from this state, a 3.6 V trickle-charge
source is used to safely condition the battery cell. The conditioning charge current is
limited to 50 mA, which for most Li-ion cells is 10% or less of the recommended CC
fast-charge current. In most instances, the battery cell voltage will be greater than
2.5 V at the time the charge request is initiated, resulting in the conditioning phase
being skipped.
There is always a small chance that the charge management block in
the GS64 power management ASIC will malfunction or fail, which
could lead to over-charging of the battery. It is strongly
recommended that any battery chosen for use with your application
has its own additional integrated over-current and over-voltage
protection.
5.8.2 Series Diode
When charging is disabled, the potential for rapid cell discharge through the body
diode inherent in the Enhancement-mode charging FET, a Schottky diode must be
placed in between the external source and the CHG_IN pin. The diode should have a
forward current and power dissipation rating consistent with its intended use, and a
maximum forward voltage drop of 0.6V.
CAUTION