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BQ76200: Design question for using BQ76200

Part Number: BQ76200

Hi There:

Our customer would like to design an 13-Cell system (with Vin =54.6V), currently design is 20A for charging, 100A for dis-charge.

The end customer would like to increase the charging current into 100A and 300A max for dis-charge.

Q1:

one BQ76200 could handle this function normally? or need add one or more BQ76200 for CHG/DSG MOS?

Q2:

The total number of CHGDSG MOS could be 12-set or much more?

Q3:

any reference design could share for this kind of application?

thanks again! 

  • Hi Kay,

    Q1.  The bq76200 does not know the current.   The MOSFETs must be able to handle the system current and the power dissipation both steady state and during switching.  Higher currents may also imply large voltage transients due to Ldi/dt, so do check switching speeds or transient suppression for the system.  Using multiple bq76200 outputs in parallel would not be recommended since if propagation delays are different one could be driving high while the other is driving low. Using separate FET groups controlled by separate bq76200 may not be desirable since a difference in the propagation delay when switching would send the load current to the slower FET group.  Some analysis may be needed to determine if the faster switching would allow the higher current. 

    Q2. The bq76200 can drive multiple FETs  The application note FET Configurations for the bq76200 ... shows examples of switching up to 12 FETs.  The internal resistances of the drivers are fixed while the external load will increase with the parallel FET gate capacitances, so note that the switching will be slower with multiple FETs.  Be sure to consider this in the safe operating area of the FETs and thermal design of their mounting. While there are other effects, if using FETs with lower capacitance more FETs could be used for the same switching speed than with higher capacitance FETs. The details in the application note bq76200 Beyond the Simple Application Schematic will be helpful for a system design, an external resistance to the FET gate is typically needed for robustness and will have an effect on the switching.

    Q3. The existing reference design is TIDA-00792, and while the FETs could handle the continuous current from their specification the thermal design is not suitable for such a high current.  I expect a system could be realized with the bq76200, but I don't know of a reference example.