Query regarding MC33771C in centralized Architecture BMS

[Vishal_Pandey]

 We are using 2 AFEs and the controller in the same board (centralized architecture) and planned to have power supplied to the Board, which will also be from the main battery which is being sensed. We are uncertain about using TPL communication between AFEs and the controller, the reason being ground of Lower AFE and the controller will be the same as the board is powered by the same battery.  We would like to know whether communication will happen with no issue if the transformer is used but the grounds are common.

1. If we are using the pulse transformer only for isolation purposes(which will not be the case in our application as the grounds are the same), can we provide  RDTX differential signals directly to the TPL transceiver with no transformer in between and the impedance is maintained uniform between Lower AFE(MC33771) and the TPL transceiver(MC33664).

[Vishal_Pandey]

Hey Jozef, 

Apart from isolation that is provided inherently  by the transformer, can I know why Transformer finds its place in this protocol, is this because of it helps in impedance matching (if that's so then I will make a way to have same impedance)? Even I will take care that Power currents from the MCU or additional IC's doesn't interfere with the sensing lines reference point.

Doesn't this be a con of this protocol especially  in centralized BMS where the board is powered by the same battery?

If I have to design a Centralized BMS  then I need the board to be powered by an Auxillary battery or have an internal isolated power supply on board. 

Regards, 

Vishal

[JozefKozon]

Hey Vishal, 

please see some of the reasons below. 

Please also refer to the section 2.6 in AN12605, which can be downloaded from docstore.

https://www.docstore.nxp.com/products/product-hierarchy?query=AN12605#button-filter-group-kind:selec...

Isolated 48 V application – capacitive coupling
For low voltage application, typically 48 V, the transformer coupling can be replaced with capacitive coupling, but the isolation is still required.

Please refer to section 3.1.3 in the AN12605.

For EMC performance and common mode noise rejection, Common Mode Chokes
(CMC) should be inserted in series with transformers. Pulse Electronic HM2102 and
HM2103 embeds internal common mode chokes and no external CMC are required.
If transformers do not embed CMC, then the external CMC should be inserted in
series with each transformer. Differential mode attenuation should not affect the 4
MHz modulation amplitude while common mode signal should be rejected. Validations
regarding attenuation should be done.

Please also refer to section 3.5 (Layout recommendation) in the AN12605.

With Best Regards,

Jozef

[JozefKozon]

Dear Vishal,

We are using 2 AFEs and the controller in the same board (centralized architecture) and planned to have power supplied to the Board, which will also be from the main battery which is being sensed. We are uncertain about using TPL communication between AFEs and the controller, the reason being ground of Lower AFE and the controller will be the same as the board is powered by the same battery.  We would like to know whether communication will happen with no issue if the transformer is used but the grounds are common.

1. If we are using the pulse transformer only for isolation purposes(which will not be the case in our application as the grounds are the same), can we provide  RDTX differential signals directly to the TPL transceiver with no transformer in between and the impedance is maintained uniform between Lower AFE(MC33771) and the TPL transceiver(MC33664).

[A]  Unfortunately your configuration wouldn't be possible. There must be a transformer between the MC33664 and MC33771. Even two transformers are recommended. There shouldn't be a common ground between the MCU and MC33771 or between the MC33664 and MC33771. There must a an isolation between the MC33664 and the AFE.

Please find attached an AN5271 describing daisy chain connection.

With Best Regards,

Jozef