AXP battery input maximum ratings

[mawe242]

Hi all,

I would like to use the AXP209 chip on my A20 SOM as a simple 3-way power management system. I don't need the PWM charger functions, so I disabled them in the driver and set the AXP to never charge the battery.

Now my question is: does anyone know what the absolute maximum voltage range of the BAT input is? Is it the same as for AC_IN and VBUS_IN (-0.3V - 11V)? Would it be safe to connect 5V to the BAT input, or do I risk frying the AXP that way?

Thanks and best regards,

MaWe

[JohnS]

I suspect those other voltage ranges are not as you posted - beware!

5V may be OK on BAT but did you read the datasheet and also check all the things connected to BAT?

The board says max 4.2 check very carefully.

John

[mawe242]

Hi John,

thanks for your answer! You are right of course, the voltage ranges I posted were the absolute maximum ratings for the inputs from the AXP209 datasheet. The A20-SOM manual speaks about 5V for 5VEXT and OTG_PWR and warns about providing "more than 5V" and that "12V would cause immediate permanent damage". It also says to connect a "4.2V battery" to BAT, but my hope is that the 4.2V rating is only because of the built-in PWM charger.

I couldn't find properly specified absolute maximum ratings for the A20-SOM itself. The "do not connect more than 5V" and "12V leads to damage" could imply that there is a little headroom on the 5V inputs.

Maybe someone from Olimex can help out? To clarify my questions:
- Is the 5V rating on 5VEXT and 5V_OTG_PWR the absolute maximum, or is there a little headroom for slightly higher voltage (up to 6V)?
- Can I connect a 6V source to the BAT input, if I disable the PWM charger of the AXP209 completely?

Thanks,

MaWe

[JohnS]

If you're finding it too hard to study datasheets then I'd just connect the right voltage.  Not hard to do, there are plenty of supplies.

John

[mawe242]

Touché :-) I guess I should have read first before adjusting my question. There's a step-up converter on the board that generates 5.1V for the "5V" rail from the AXP IPSOUT. And as IPSOUT always follows the currently active AXP input, connecting more than 5V to any SOM power input seems to be a bad idea...

Ok, but my original question (if 5V on BAT would be ok) can only be partly answered by looking at the datasheets. The SOM-side of things seems to be ok (all caps on BAT rated at 6.3V, apart from one 0.1uF without rating, nothing else connected to BAT). But whether the AXP can cope with 5V on BAT, BATSENSE, CHSENSE and LX1, that information is lacking from the AXP datasheet. Or I'm too blind to see it...

Anyway, thanks for your input.

MaWe