AXP202 datasheet(18/48 Pages) ETC2

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Single Cell Li-Battery PWM Charger and Power System Management IC

AXP202

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

default. In this mode, AXP202 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, AXP202 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.

AXP202’s Reaction to External Power Supply Plugin

AXP202 can automatically detect the plugin of external powersand judge whether the power is usable

or not. The result will be set in corresponding registers, and IRQ will be released to inform the Host at

the same time.

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

Bits

Description

REG00H[7]

Indicating the presence of external ACIN

REG00H[6]

Indicating whether the external ACIN is usable or not

REG00H[5]

Indicating the presence of external VBUS

REG00H[4]

Indicating whether the external VBUS is usable or not

REG00H[3]

Indicating whether the VBUS voltage is above VHOLD when used

REG00H[1]

Indicating whether ACIN/VBUS short circuits on PCB or not

REG00H[0]

Indicating whether the system is triggered to startup by ACIN/VBUS

or not

The status bit of “indicating whether the VBUS voltage is above VHOLD or not when used” enables 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 power

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