FUNCTIONAL DEVICE OPERATION
BATTERY INTERFACE AND CONTROL
The precharge will time-out and stop charging, in case it did not succeed in raising the battery to a high enough level: BATTON
for internal precharge, external precharge in the case of USB, and BPON for the external precharge, in case of a charger. This
is a fault condition and is flagged to the processor by the CHGFAULTI interrupt, and the CHGFAULTS[1:0] bits are set to 10.
The charging circuit will stop charging and generate a CHGCURRI interrupt after the battery is fully charged. This is detected
by the charge current dropping below the CHGCURR limit. The charger automatically restarts if the battery voltage is below
BATTCYCL. Software can bypass this cyclic mode of operation by setting the CYCLB bit. Setting the bit does not prevent
interrupts to be generated.
During charging, a charge timer is running. When expiring before the CHGCURR limit is reached, the charging will be stopped
and an interrupt generated. The charge timer can be reset before it expires by setting the self clearing CHGTMRRST bit. After
expiration, the charger needs to be restarted. Proper charge termination and restart is a relatively slow process. Therefore in both
of the previous cases, the charging will rapidly resume, in case of a sudden battery bounce. This is detected by BP dropping
below the BATTON threshold.
Out of any state and after a time-out, the charger state machine can be restarted by removing and reapplying the charger. A
software restart can also be initiated by setting the self clearing CHGRESTART bit.
The state of the charger logic is reflected by means of the CHGENS bit. This bit is therefore a 1 in all states of the charger
state machine, except when in a fault condition or when at the end of charge. In low power boot mode, the bit is not set until the
ACKLPB bit is set. This also means that the CHGENS bit is not cleared when the power limiter interacts, or when the battery
temperature is out of range. The charge LED At CHRGLED follows the state of the CHGENS bit with the exception that software
can force the LED driver on.
The detection of a serial path versus a single path is reflected through the CHRGSSS bit. A logic 1 indicates a serial path. In
cases of single path, the pin BATTFET must be left floating.
The charging circuit will stop charging, in case the die temperature of the IC exceeds the thermal protection threshold. The
state machine will be re-initiated again when the temperature drops below this threshold.
Table 77. Charger Timer Characteristics
Parameter
Charger Timer
Condition
Min
Typ
120
270
Max
Units
min
-
-
-
-
External precharge 80 mA
Internal precharge 40/80 mA
min
Precharge Timer
External precharge 400/560 mA
-
60
-
min
Table 78. Charger Fault Conditions
Fault Condition
Cleared or no fault condition
Over-voltage at CHRGRAW
Excessive dissipation on M1/M2
Sudden battery drop below BATTMIN
Any charge time-out
CHGFAULTS[1:0]
CHGFAULTI
Not generated
Rising edge
Rising edge
Rising edge
Rising edge
Dual edge
00
01
01
10
10
11
Out of temperature
SOFTWARE CONTROLLED CHARGING
The charger can also be operated under software control. By setting CHGAUTOB = 1, full control of the charger settings is
assumed by software. The state machine will no longer determine the mode of charging. The only exceptions to this are a charger
removal, a charger over-voltage detection and excessive power dissipation in M1/M2.
For safety reasons, when a RESETB occurs, the software controlled charging mode is exited for the standalone charging
operation mode.
In the software controlled charging mode, the internal trickle charger settings can be controlled as well as the M3 operation
through FETCTRL (1 = conducting). The latter is only possible if the FETOVRD bit is set. If a sudden drop in BP occurs (BP <
BPON) while M3 is open, the charger control logic will immediately close M3 under the condition that BATT > BATTMIN.
13892
Analog Integrated Circuit Device Data
96
Freescale Semiconductor
FREESCALE [ Freescale ]
