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BQ76920: Power management forum

FJ
Intellectual 340 points
Part Number: BQ76920
Other Parts Discussed in Thread: UCC27511A

I am reviewing a BMS design that uses the BQ76920 and drives 8 CHARGE and 8 DISCHARGE FETS using drive circuitry that utilizes a HEF4011BT NAND Gate.   This is for a high power design that is claimed to handle a 12 Volt LIFE pack and provide up to 200A continuous and 800A pulse.

My question is, does the drive circuitry using the NAND gate provide an increase in drive current to control the CHG and DSG gates?  Would this type of design out perform or have an advantage over using specific gate drives like the UCC27511A?

  • 0
    TI__Guru 54715 points

    Hi FJ,

    4000 series logic was one of the early logic families, is still a popular high voltage logic option, and has been used with quite a lot of versatility in many applications.  Looking at the data sheet IOH/IOL magnitude is 3.4 mA for each driver at 1.5V from each supply.  The UCC27511A output capability is listed as 4A/8A so the driver is much more capable.  In your schematic clip the current to the gates will be limited by 1k R9 (and R3 if these are individual for each FET)  So with a 12V drive you can only get less than 12 mA.  Looking at one of the FETs note Ciss is 18 nF, for 8 144 nF. I would expect R9 might need some adjustment for a final value for high current switching.  The driver is likely more capable and predictable.  Posting a specific question for the driver people may be helpful if you have a question on its application.