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LM5012-Q1: Do the COT regulator suitable for bootstrap load?

Roberto Schembari
Prodigy 80 points
Part Number: LM5012-Q1


Tool/software:

Hello,

In a 48V drive, I have to supply hi-side mos drivers with bootstrap circuits and a 48 to 15V dcdc.

In this case the load is always impulsive, when low side mos make the transition from OFF to ON, both for low side operation and for hi side bootstrap capacitor charge. I put a 2R2 resistor for bootstrap current limit, and I have 47uF in the supply of hi-side drivers. The maximum voltage difference between hi side supply and the output of DCDC, during normal operation, is 4.4V, so the maximum peak current is 2A.

For reduce DCDC output voltage drop, due impulsive load, I put a 470uF of electrolytic capacitor and 10uF of ceramic capacitor.

The question is: is the COT regulator suitable for this impulsive load?
Do you have some hints for the converter stability?

Thanks

  • +1
    TI__Expert 5520 points

    Hi Roberto,

    You can use the COT based architecture due to it's  superiority on it's transient response compare to voltage or current mode control. However you need to be careful while choosing the output capacitor value. If the output capacitor value is too high, it might take more time to charge the bootstrap capacitor which might cause the low side turn-on time limitation and hence the switching frequency of operation. If the output cap is very low, there is a possibility of hitting bootstrap UVLO level. 

    If there a provision, i would use the LDO as bootstrap supply over DC-DC converter due to simple architecture, BOM cost and overall solution size.

    Thanks,

    Nitya