LTC7060 BGVcc Current Draw Clarification

I do notice that for the reference design included in the LT7872 LTspice example circuit which includes LTC7060s whose BGVcc is powered from the DRVcc pin, 1.6A pulses are drawn from the LT7872's DRVcc pin, which is rated for only 150mA on the datasheet.

Hello, I have adjust BST's input source to a lower voltage, and am seeing only 3-4A of peak pulsed current at all pins mentioned previously..

Hello Michael,

The maximum current rating for the LTC7872’s DRVCC pin is 150mA DC. Per the simulation, the DRVCC current is 28.5mA DC. Therefore, it is well within the rating. The DRVCC current can be estimated from the switching supply current vs load capacitance curve from your post. It can also be calculated with the formula below:

IGATECHG = f * (QT + QB) * N

Where f = switching frequency

QT = total gate charge for the top MOSFET(s) per phase

QB = total gate charge for the bottom MOSFET(s) per phase

N = # of phases

The DRVCC and gate drive current noise is due to the following:

• The noise on the LTC7872 DRVCC pin’s current is due to the charging of the bottom MOSFET's gate to source capacitance and the refresh of the boost capacitor.
• The noise on the LTC7060 BST pin’s current is due to the charging of the top MOSFET's gate to source capacitance.
• The noise on the LTC7060 TG pin’s current is due to the charging and discharging of the top MOSFET’s gate to source capacitance.

The actual noise on the PCB will be much smaller than in the simulation due to the trace impedance and the ESR/ESL of the boost capacitor, BGVcc capacitor and DRVCC capacitor.

Best regards,

Mike

Thank you for the clear answer Mike, I appreciate it. I will include some high frequency bypass capacitors at the LDO output as a precaution.

Regards,
Michael