Other Parts Discussed in Thread: BQ76940, , INA169, BQ76200
Hi,
I'm in the process of considering the reference design of the TIDA-00792 for use in a 60V high power audio amplifier. I noticed from reading the various documents you provide and studying the schematics that the Rsense used by the BQ76940 is placed in the low side return path from PACK- to BAT-. This concerns me a little as it would seem to assume that the PACK- can be considered as a floating connection (from the perspective of your design documentation). i.e. It is not tied to the same high power ground point as the negative side of the battery.
In my application I will have the PACK- as my ground point for all the rest of the system and indeed tied to earth as I will be accepting several line level inputs which will be ground referenced. These analogue signal lines will clearly not take very kindly to a floating ground on the amplifier system, considering that under heavy loads, PACK- could be 20mV higher than BAT- across the sense resistor.
Having considered this I assume that I must be very careful to ensure that in such an application the BAT- is floating with respect to my system GND and should therefore also never be earthed, and that all currents associated with signal connections from the BMS to other parts of my system must share the GND return path through Rsense. If I have connectors that use shielded cables, these must be isolated at the point of interconnect and that I can expect to see the Rsense voltage fluctuations superimposed on all signalling lines between the BMS and the system which has its GND attached to PACK-.
Could you please confirm that this is expected and further to this can you also comment on the possibility of moving Rsense onto the high side and level shifting down using some dedicated high side current measuring differential amp such as the INA169. Although more complex it would avoid the necessity to ensure these ground traces are isolated between the powered system and the BMS.
Thanks in advance
Aidan
