13892 datasheet(95/156 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

13892

FUNCTIONAL DEVICE OPERATION

BATTERY INTERFACE AND CONTROL

CHARGER OPERATION

USB CHARGING

The USB VBUS line in this case, is used to provide a supply within the USB voltage limits and with at least 500 mA of current

drive capability.

When trickle charging from the USB cable, it is important not to exceed the 100 mA, in case of a legacy USB bus. The

appropriate charge current level ICHRG[2:0] = (0001) is 80 mA typical which accounts for the additional current through the

charge LED indicator.

WALL CHARGING

No distinction can be made between a USB Host or a wall charger. Therefore, when attaching a wall charger, the CHRGSE1B

pin must be forced low as a charger attach indicator. The CHRGSE1B pin has a built-in weak pull-up to VCORE. In the

application, this pin is preferably pulled low, with for instance an NPN of which the base is pulled high through a resistor to

CHRGRAW. The state of the CHRGSE1B pin is reflected through the CHRGSE1BS bit. When CHRGSE1B changes state a

CHRGSE1BI is generated. No specific debounce is applied to the CHRGSE1B detector.

Table 76. Charger Detector Characteristics

CHRGSE1B Pull Up

To VCORE

100

kOhm

Logic Low

0.3

Logic High

1.0

VCORE

If an application is to support wall chargers and USB on separate connectors, it is advised to separate the VBUS and the

CHRGRAW on the PCB. For these applications, charging from USB is no longer possible. For proper operation, a 120 kOhm

pull-down resistor should be placed at VBUS.

STANDALONE CHARGING

A standalone charge mode of operation is provided to minimize software interaction. It also allows for a completely discharged

battery to be revived without processor control. This is especially important when charging from a USB host or when in single

path configuration (M3 replaced by short, BATTFET floating). Since the default voltage and current setting of the charge path

regulator may not be the optimum choice for a given application, these values can be reprogrammed through the SPI if the

CHGAUTOVIB bit is set. Note that the power limiter can be programmed independent of this bit being set.

Upon connecting a USB host to the application with a dead battery, the trickle cycle is started and the current set to the lowest

charge current level (80 mA). When the battery voltage rises above the BATTON = 3.4 V threshold, a power up sequence is

automatically initiated. The lowest charge current level remains selected until a higher charge current level is set through the SPI

after negotiation with the USB host. In case of a power up failure, a second power up will not be initiated to avoid an ambulance

mode, the charger circuitry will though continue to charge. The USB dead battery operation following the low power boot scheme

is described further in this chapter.

Upon connecting a charger to an application with a dead battery the behavior will be different for serial path and single path

configurations.

In serial path (M3 present), the application will be powered up with the current through M1M2 set to 500 mA minimum. The

internal trickle charge current source will be enabled, set to its lowest level (40 mA) up to BATTMIN, followed by the highest

setting (80 mA). The internal trickle charge current is not programmable, but can be turned off by the SPI. In this mode, the

voltage and current regulation to BP through the external pass devices M1M2 can be reprogrammed through the SPI. Once the

battery is greater than BATTON, it will be connected to BP and further charged through M1/M2 at the same time as the

application.

In single path (M3 replaced by a short, BATTFET floating), the battery (and therefore BP) is below the BPON threshold. This

will be detected and the external charge path will be used to precharge the battery, up to BATTMIN at the lowest level (80 mA),

and above at the 500 mA minimum level. Once exceeding BPON, a turn on event is generated and the voltage and current levels

can be reprogrammed.

When in the serial path and upon initialization of the charger circuitry, and it appears BP stays below BPON, the application

will not be powered up, and the same charging scheme is followed as for single path.

Parameter

Condition

Min

Typ

Max

Units

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