FUNCTIONAL DEVICE OPERATION
BATTERY INTERFACE AND CONTROL
INTERNAL TRICKLE CHARGE CURRENT SOURCE
An internal current source between BP and BATTISNS provides small currents to the battery in cases of trickle charging a
dead battery. As can be seen under the description of the standalone charging, this source is activated by the charger state
machine, and its current level is selected based on the battery voltage. The source can also be enabled in software controlled
charging mode by setting the TREN bit. This source cannot be used in single path configurations because in that case,
BATTISNS and BP are shorted on the board.
Table 69. Internal Trickle Charger Control
BATT
Trickle Charge Current (mA)
0 < BATT < BATTMIN
40
80
BATTMIN < BATT < BATTON
Table 70. Internal Trickle Charger Characteristics
Parameter
Condition
Min
Typ
Max
Units
Trickle Charge Current Accuracy
-
0
-
-
-
-
30
-
%
V
V
V
BATTISNS
Operating Voltage
BP-BATTISNS
BP-BATTISNS
1
-
Extended Operating Range (68)
0.3
-
Notes
68. The effective trickle current may be significantly reduced
CHARGER DETECTION AND COMPARATORS
The charger detection is based on three comparators. The “charger valid” monitors CHRGRAW, the “charger presence” that
monitors the voltage drop between CHRGRAW and BPSNS, and the “CHGCURR” comparator that monitors the current through
the sense resistor connected between CHRGISNS and BPSNS. A charger insertion is detected based on the charger presence
comparator and the “charger valid” comparator both going high. For all but the lowest current setting, a charger removal is
detected based on both the “charger presence” comparator going low and the charger current falling below CHGCURR. In
addition, for the lowest current settings or if not charging, the “charger valid” comparator going low is an additional cause for
charger removal detection. The table below summarizes the charger detection logic.
Table 71. Charger Detection
Charger Valid
Comparator
Charger Presence
Comparator
Setting ICHRG[3:0]
CHGCURR Comparator
Charger Detected
0
1
X
0
1
0
1
X
X
X
X
0
No
No
0000, 0001
1
Yes
No
X
X
X
Other Settings
X
1
Yes
Yes
In addition to the aforementioned comparators, three more comparators play a role in battery charging. These comparators
are “BATTMIN”, which monitors BATT for the safe charging battery voltage, “BATTON”, which monitors BATT for the safe
operating battery voltage, and “BATTCYCL”, which monitors BPSNS for the constant current to constant voltage transition. The
BATTMIN and BATTON comparators have a normal and a long (slow) debounced output. The slow output is used in some places
in the charger flow to provide enough time to the battery protection circuit to reconnect the battery cell.
Table 72. Charger Detectors main characteristics
Parameter
BATTMIN Threshold
BATTON Threshold
BATTCYCL Threshold
Charger Presence
Condition
Min
2.9
3.3
-
Typ
Max
3.1
3.5
-
Units
Volts
Volts
%
At BATT
At BATT
-
-
At BPSNS relative to VCHRG[2:0]
CHRGRAW-BPSNS
98
-
10
50
mV
13892
Analog Integrated Circuit Device Data
Freescale Semiconductor
93
FREESCALE [ Freescale ]
