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BQ76930: 20S battery management

Lenna Yan
Intellectual 1960 points
Part Number: BQ76930
Other Parts Discussed in Thread: BQ78350, ISO1541, TIDA-01093

BQ76930

Hi team,

The customer has some issues in high power battery management.

The target battery pack is Panasonic NCR18650B 20S in series, and the 15S battery pack connected in parallel. What should be noticed when designing?

1. The current solution uses two sets of BQ76930 & BQ78350 in series and uses the MCU to read two modules’ electricity. Single 10S module can work normally. This will be faster and can reduce design risk. Is the design reasonable?

2. The customer designed the 20S system according to TIDA – 01093. The circuit of CHG DSG was modified based on the 10S circuit. The other parts are the same as 10S circuit, just add ISO1541 on the circuit. Is there a risk to this design?

3. Two BQ76930 detect the current simultaneously, but can the SPR SRN of high side BQ76930 withstand such high voltage? The customer thinks that is ok. But when detecting current in high power condition, useless consumption will be high.

 


  • 0
    TI__Guru 54715 points
    Hi Lenna,
    When paralleling batteries be sure that the system can match the voltage before batteries are connected, otherwise large current may flow from one battery to the other and both may fault.
    1. The bq76930 low side FET protection can tolerate reverse voltage if the FETs are sized correctly. There will be leakage current into the clamp for CHG, this will occur if either 10S circuit protects with load, be sure this is acceptable.
    2. TIDA-01093 used a common FET drive. If the FET drive is returned to individual 10S modules the reverse voltage noted in #1 above must be considered.
    3. The top bq76930 would need a sense resistor connected at its VSS potential which would be connected at the 10th cell of the total system, it would not see a high voltage on these pins. The bq78350 needs to know current for its gauging operation, so the second sense resistor is needed. Due to the low levels translating the voltage from a common sense resistor to a different potential does not seem practical. The double power loss from the 2 sense resistors and 2 sets of FETs is one of the reasons for the TIDA-01093 design with a single FET pair and single sense resistor. Each system designer must decide what is OK for their system.