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UCC21530-Q1: Bootstrap capacitor

Part Number: UCC21530-Q1
Other Parts Discussed in Thread: UCC21530

Regarding boostrap capacitor, what are recommandations from TI when we have no switching commutation for a long period of time (>30s).

Shall we start we a precharge of boost strap capacitor (100 % low side  switch ON) ? Is there any mechanism, except UVLO, into gate driver to prevent insufficient gate voltage ?

What is the maximum time to discharge a 1uF boostrap capacito @ 25V if there is no switching commutation for a long period of time (minimum leakage or quiescent current at vddx)?

  • Hi Sebastien, 

    There's no other mechanism besides UVLO to prevent insufficient gate voltage. When the VDD drops to below UVLO, the output will be off at all times until the VDD recovers to above UVLO. 

    If we're looking at the capacitor discharge formula and take all operating condition into consideration (1uF bootstrap capacitor, VDD dropping from 25V to below UVLO, and quiescent current of 1.8mA max), the time it takes to discharge the capacitor is much less than 1 second. Thus, if there's >30 seconds in between the pulses, the VDD voltage will fall below UVLO and driver will no longer have output. 

    You can experiment with 100% low side switch ON to charge the bootstrap capacitor. In the meantime, if you want a part number with higher VDD UVLO, I would recommend our latest gate driver family, UCC2155x. It has improved robustness against the UCC21530 family, and has option for a 17V UVLO. 

    Thank you!