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BQ76940: FET Configurations

Part Number: BQ76940
Other Parts Discussed in Thread: BQ76200, , BQ78350, , BQ78350-R1

I found the SLVA729A "FET Configurations for the bq76200 High-Side N-Channel FET Driver" and in this document there are multiple examples of parallel and series connected fets.

www.ti.com/.../slva729a.pdf

the document states it uses the bq769400 and bq78350 in the test setups (Table 1. Test Configurations).

so my question how to configure the 78350 and bq769400 for a parallel mosfet setup?

  • Hi Manfred,
    The bq78350 was used for the demonstration of the parallel FETs since it was a convenient platform for automatic control of the FETs . In practice the bq78350 does not support parallel FETs well because of the body diode protection built into it. When there is a charge fault, with sufficient discharge current the charge FET will be turned on again to prevent heating of the charge FET in the series FET configuration. Similarly the discharge FET will be turned on with sufficient charge current during a discharge fault. Current information is available to the bq78350 from the bq76940 on 250ms intervals. With separate paths and charger and load simultaneously present the FETs may cycle and allow undesired continued charge or discharge. Additionally the bq78350-R1 has only the VAUX input available to monitor the condition of the PACK+ voltage. With separate paths a system may want to monitor charger and load voltages separately for fault recovery and behavior decisions.
    The series FET configuration is not immune to having FETs cycle if there is a simultaneous load and charger, particularly if the load changes or has a delayed start. So your system still needs to have control of its current paths.
    If you use the bq78350-R1 for parallel paths there is no special configuration, be aware and accommodate these behaviors in your system design, see the technical reference manual for available configurations.