Intel PXA27X manual Batteries, Main Battery, Backup Battery

Intel® PXA27x Processor Family Power Requirements

these supplies must come up at the required voltage to operate reliably and to avoid damage to the external components. VCC_IO must be the highest potential of the system I/O supplies1. VCC_IO can be connected to any of VCC_LCD, VCC_MEM, VCC_USIM, VCC_USB and VCC_BB, but none of these supplies can exceed VCC_IO.

The power-up voltage requirement must be communicated by some input strapping mechanism on the PMIC if a PMIC can provide more than one voltage level for any of these domains. This ensures that each regulator powers up to its designated voltage without processor intervention. Software must read this configuration information using an I2C command.

2.2Batteries

The PXA27x processor supports a variety of system battery configurations with both a main battery and backup battery, and a main battery alone.

In systems with only a main battery, the main battery must drive VCC_BATT directly or use a regulator. In systems with a backup battery, the backup battery connects directly to VCC_BATT or the backup battery can be connected to a power controller, which in turn drives the PXA27x processor VCC_BATT.

2.2.1Main Battery

The main battery is a rechargeable single cell (or multiple cells in parallel) using lithium-ion or lithium-polymer technology. These batteries typically present a voltage as high as 4.2 V when fully charged, declining to under 3.0 V as they discharge. A main battery capacity of 500 to 1200 mAh is typical for most applications.

2.2.2Backup Battery

The backup battery is a lithium or lithium-manganese coin cell with an output voltage of approximately 3.0 V. The backup battery is a small rechargeable coin cell permanently mounted to the printed circuit board (PCB) in many handset applications. The PMIC must include a regulator and associated circuitry for recharging this type of backup battery. The two backup battery configurations are shown in Table 6.

1.excluding VCC_BATT and VCC_USB

14 Application Note