AXP221

The AXP221 is the PMIC (Power Management IC) used by A31 SoCs and developed by X-Powers, a sister company of Allwinner.

Overview
The AXP221 is a highly integrated power management IC, targeted at single cell battery (Li-ion or Li-Po) applications needing multiple power conversion outputs. It is complete power solution that is both versatile and easy to use, satisfying the precise and complicated needs of multi-core systems.

The AXP221 integrates a USB 3.0 compatible flash charger, which has a 94% maximum efficiency, and a charging current of up to 2.2A. At the same time, it supports up to 21 power outputs (including 5 high-current DC-DC outputs, with efficiencies of up to 95%), and also multiple 12-bit ADC channels to monitor voltage, current, and temperature. To insure safe and smooth operation of the power system, the AXP221 also integrates over/under voltage, over current, overheating protection.

Regulators
The AXP221 features 5 DC-DC step-down (buck) converters, 14 linear regulators (5 of which are low-noise), and 2 switches. The DC-DC converters operate in automatic (PFM + PWM) or PWM mode, controllable via reg 80h, at a default frequency of 3 MHz. The frequency is controlled via reg 37h. It also supports spread spectrum.

Interrupts
This section corresponds to section 9.8 in the datasheet.

The AXP221 pulls the IRQ pin low to signal an interrupt to the host, and stores the interrupt status in the interrupt status registers (48h ~ 4Ch). Writing 1 to the corresponding bit clears the interrupt. When there are no interrupts, the IRQ pin is pulled up (by an external 51KΩ resistor). Each interrupt can be masked via the interrupt control registers (40h ~ 44h).

REG 04-0Fh: Data storage
As long as power exists, this data will be kept, not affected by system power off.

REG 10h: Regulator output control
Default value: XXH

REG 12h: Regulator output control
Default value: XXH

REG 13h: Regulator output control
Default value: 01H

REG 31h: Wake-up control and VOFF - Shutdown voltage setting
Default value: 03H

REG 32h: Shutdown control, battery detection and CHGLED pin control
Default value: 43h

REG 33h: Charge control 1
Default value: C6H

REG 34h: Charge control 2
Default value: 45h

REG 35h: Charge control 3
Default value: 0Eh

Interrupts
See Interrupts section.

Spec Sheets
AXP221 Datasheet v1.2 (PDF, 52 pages, 2013-03-26)