Diodes APM8600 - Manual (Page 10)

APM8600
SINGLE CELL LINEAR LITHIUM BATTERY CHARGER
WITH 28V OVP AND PROGRAMMABLE CHARGE TIMER
APM8600
Document number: DS35140 Rev. 1 - 2
10 of 14
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December 2010
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UC
T
Functional Description (continued)
CHARGING PROCESS DESCRIPTION
The charging process is as follows, working through the state diagram.
The device will begin in the Disable state as the input power supply ramps from 0V. Once the input power supply has got
into the valid range (4.15V – 7V), and the device is enabled then it will enter the Prequal state. This state allows for slow
charging of a severely discharged battery. If the battery is already partially charged then the condition to move into the
Charge
state is met. If it is not then the slow charge will increase the battery voltage until it can enter the Charge state, or if
the voltage does not rise sufficiently before the charge timer runs out (set using the capacitor on the CT pin) then the device
will go into the Fault state, indicating that the battery cell may be damaged or has failed and is not taking charge. In the
Prequal
state the battery temperature can be monitored with a 10k NTC thermistor connected to the THM pin, and if the
battery temperature goes out of range (above ~50°C or below ~0°C, depending on thermistor choice) then charging will be
suspended with the device going into the THM state.
Once the battery has charged to a level of 3V, the device enters the Charge state, allowing faster charging of the battery in
its normal voltage range, with 10 times the current used in the Prequal state. For information on setting the charge currents,
see the functional description of the SETI pin. Again, the battery temperature is monitored and charging will be suspended if
the temperature goes out of range. The Charge state will last until the current drawn by the battery drops to 7.5% of the full
charge current. The device will then enter the Top-Off state, maintaining battery voltage and providing top-off charging
current for the time defined by the C
T
value. Once that timer completes, the device will enter the Done state, with zero
battery current. If the battery voltage falls below 4.05V then the device will automatically return to the Charge state.
DONE TOP-OFF CHARGE PREQUAL DISABLE
EN
CHG
V
BAT
I
BAT
t
0V
I
PREQUAL
150/R
SETI
0A
I
CHARGE
1500/R
SETI
3V
4.2V
I
TOPOFF
112.5/R
SETI