AXP209 datasheet(18/45 Pages) ETC2

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AXP209

Enhanced single Cell Li-Battery and Power System Management IC

The Host can set IPS parameters and read the feedback by using internal registers in AXP209 via

TWSI.

Voltage Limiting/Current Limiting mode and Direct Mode

In order not to affect the USB communication, VBUS is always working under Voltage-Limit mode by

default. In this mode, AXP209 ensures that VBUS voltage remains above a configurable reference

voltage VHOLD which can meet the USB specification. The default VHOLD is 4.4V, adjustable in

Reg30H [5:3] register.

If the system has limit on current obtained from USB VBUS, a current-limit mode is provided (See

REG30H[1] register), with 900mA/500mA/100mA (Reg30H [0]) selectable.

If the system just utilizes the USB for power supply rather than communication, or the USB power

adapter is utilized, AXP209 can be set to “VBUS Direct Mode” by modifying register REG30H[6], and

then AXP202 will give priority to the application power demand. When the drive ability of USB Host is

insufficient or system power consumption is large then the VBUS voltage is lower than VHOLD,

AXP202 will release IRQ to indicate the weak power supply ability of Host VBUS, which may affect

USB communication, and then Host software will follow up.

AXP209’s Reaction to External Power Supply Connection

AXP209 can automatically detect the connection of external power and judge whether the power is

usable or not. The result will be set in corresponding registers, and IRQ will be asserted to inform the

Host at the same time.

The following table has listed the status bits and meanings of external power registers:

Status register bits

Description

The status bit indicating “whether the VBUS voltage is above VHOLD or not when used” allows the Host

to judge when it receives IRQ7 (indicating weak supply ability) whether VBUS is pulled low by system

load input or the external power itself is below VHOLD, which may facilitate Host software to decide

either to keep on working in Voltage-Limit mode or switch to Direct Mode.

When to Select VBUS as Input Power

N_VBUSEN and register REG30H[7]: is used to determined when shall VBUS be used as the power

supply

N_VBUSEN

REG30H [7] Input Power

Description

Low

VBUS

Select if VBUS is valid and no ACIN is

available

Low

VBUS

Select if VBUS is valid

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