topic Re: FS26 - Read VBAT via AMUX by MCU, voltage levels? in Power Management

FS26 - Read VBAT via AMUX by MCU, voltage levels?

HerrBert — Thu, 13 Mar 2025 08:19:35 GMT

Hello!

I am designing a BMS and trying to figure out how to mux the BATSENSE Pin to the AMUX output of the FS26, then reading it by ADC via an external MCU. I am not sure about the voltage levels between the two devices, see below:

In the datasheet it says for AMUX: "Absolute max rating -0,3 - 5,5V".
I would bet that the input range of BATSENSE pin is is divided down to the 0-5V scale. But since I cannot find more information on that I cannot rely on just the "idea".
Or does that only apply to voltage that is being applied from the outside world to that pin?

Unfortuantely the datasheet is very unclear with more information on how to use that feature.

My question is, what appears on the AMUX pin when BATSENSE is muxxed to it? Can I read that with an MCU without external adaption?

Can someone help please?

Product page:
https://www.nxp.com/products/FS26#documentation

Datasheet:
https://www.nxp.com/docs/en/product-brief/FS26_PB.pdf

Re: FS26 - Read VBAT via AMUX by MCU, voltage levels?

TomasVaverka — Thu, 13 Mar 2025 12:01:05 GMT

Hello Stephan,

You are referring to the FS26 Product brief, while more info can be found in the FS26 Full datasheet (Secure file requiring an NDA).

The BATSENSE pin voltage is divided down before being output to AMUX (AMUX[4:0] = 0b10110). The divider ratio is configurable using the AMUX_DIV bit, with options of 7.5 (default) or 14. The AMUX output voltage range is 0.3V to 3.0V.

If your MCU ADC has an input range of 0-3V or higher, you can read AMUX directly. If it has a lower input range (e.g. 0-1.8V), you will need a voltage divider or scaling circuit.

Example calculation:
If BATSENSE = 12V:
Divider ratio 7.5 (AMUX_DIV = 0) → AMUX output = 12V/7.5 = 1.6V
Divider ratio 14 (AMUX_DIV = 1) → AMUX output = 12V/14 = 0.86V

BRs, Tomas

Re: FS26 - Read VBAT via AMUX by MCU, voltage levels?

HerrBert — Thu, 13 Mar 2025 12:07:26 GMT

Thank you.

Yes, the information is available in the full datasheet I found on the product site und "secure" documents, an hour ago.

Nonethe less, thank you for clarifying!

I think this information is well hidden for given the case that is crucial for working with the component.

Thank you for the reply...