L99BM114: Wiring clarification for Unmounted Cells (5S configuration) - Section 6.8

[_gabrielfbdiniz_]

Hello everyone,

We are currently designing a decentralized Battery Management System (BMS) node for our Formula SAE electric car. We selected the L99BM114 due to its robustness in automotive environments and high measurement accuracy.

Our architecture requires this specific node to monitor a 5-series (5S) cell module. Since the L99BM114 supports up to 14 series cells, we will have 9 unused channels.

While reviewing Section 6.8 of the datasheet (Unmounted cells), the exact hardware implementation for our case felt a bit ambiguous. We want to ensure our schematic doesn't trigger false internal diagnostics, such as Cell Open Wire or Balancing Short/Open.

Could anyone clarify the recommended wiring for the unused pins in a 5S configuration? Specifically:

1. Voltage Sense Pins (C6 to C14): Should all these unused inputs be shorted together and tied to the highest active potential (C5)?

2. Balancing Pins (S and B) & Filtering: How exactly should we handle the external filtering resistors (RLPF) and the S/B balancing pins for these 9 unused channels? Should they be left floating, or is there a specific pull-up/pull-down tie-off required?

If there is any reference schematic or application note that covers a reduced cell count configuration for this IC, that would be incredibly helpful.

Thanks in advance for the support!

[Max VIZZINI]

Hi,

You need to connect all sensing and balancing pins need to be shorted in series or the IC will not properly work.

The first 2 and the last 2 cells HAVE to be connected, and minimum number is 4 cells. 

I attach below a project we did for 6 cells battery.

Best Regards,

AutoDevKit Team

[Max VIZZINI · Accepted solution]

Hi,

This could be for 5 cells:

When building your new board, please follow the yellow box highlighted in the datasheet, all sensing and balancing have to be short-circuited at pcb level.

Best Regards,

AutoDevKit Team