FUNCTIONAL DEVICE OPERATION
BATTERY INTERFACE AND CONTROL
BATTERY INTERFACE AND CONTROL
The battery management interface is optimized for applications with a single charger connector to which a standard wall
charger or a USB host can be connected. It can also support dead battery operation and unregulated chargers.
CHARGE PATH
CHARGER LINE UP
The charge path is depicted in the following diagram.
Figure 26. Charge Path Block Diagram
Transistors M1 and M2 control the charge current and provide voltage regulation. The latter is used as the top off change
voltage, and as the regulated supply voltage to the application in case of a dead battery operation. In order to support dead
battery operation, a so called “serial path” charging configuration including M3 needs to be used. Then in case of a dead battery,
the transistor M3 is made non-conducting and the internal trickle charge current charges the battery. If the battery is sufficiently
charged, the transistor M3 is made conducting which connects the battery to the application just like during normal operation
without a charger. In so called single path charging, M3 is replaced by a short and the pin BATTFET must be floating. Dead
battery operation is not supported in this case. Transistors M1 and M2 become non-conducting if the charger voltage is too high.
The VBUS must be shorted to CHRGRAW in cases where the wall charger and VBUS voltages are contained on a common pin.
A current can be supplied from the battery to an accessory with all transistors M1, M2, and M3 conducting, by enabling the
reverse supply mode. An unregulated wall charger configuration can be built, in which case CHRGSE1B must be pulled low. The
battery current monitoring resistor R1 and the charge LED indicator are optional. More detail on the battery current monitoring
can be found in ADC Subsystem.
The preferred devices for M1 and M2 are Fairchild™ FDZ193P, due to their small package outline and thermal characteristics.
The preferred device for M3 is the On Semiconductor NTHS2101P for its low RDSON and small footprint.
CHARGER SIGNALS
The charger uses a number of thresholds for proper operation and will also signal various events to the processor through
interrupts. Table 61 summarizes the main signals given, including the control bits. For details see the related sections in this
chapter and the SPI bit summary in SPI Bitmap.
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Analog Integrated Circuit Device Data
88
Freescale Semiconductor
FREESCALE [ Freescale ]
