13892 datasheet(93/156 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

13892

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

0 < BATT < BATTMIN

BATTMIN < BATT < BATTON

Table 70. Internal Trickle Charger Characteristics

Trickle Charge Current Accuracy

Operating Voltage

BATTISNS

BP-BATTISNS

Extended Operating Range (68)

BP-BATTISNS

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

0000, 0001

Yes

Other Settings

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.

BATT

Trickle Charge Current (mA)

Parameter

Condition

Min

Typ

Max

Units

Setting ICHRG[3:0]

Charger Valid

Comparator

Charger Presence

Comparator

CHGCURR Comparator

Charger Detected

Table 72. Charger Detectors main characteristics

Parameter

Condition

Min

Typ

Max

Units

BATTMIN Threshold

At BATT

2.9

3.1

Volts

BATTON Threshold

At BATT

3.3

3.5

Volts

BATTCYCL Threshold

At BPSNS relative to VCHRG[2:0]

Charger Presence

CHRGRAW-BPSNS

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