Hello guys,
One of my customers is evaluating LM5019 on their own board. They found about 1.2A peak current (triangle shape and the current width of base is 20ns) is flowed into VIN terminal when high side NMOS is turned on. (Any peak current like above is not observed when the high side NMOSFET is turend off.)
I think the current is used for SW terminal node charge up to VIN voltage. But the customer thinks it is a through current from VIN to RTN(GND). Which is correct?
Their power supply condition uses LM5019 is the follow. VIN=60V, Vout=5V, Iout=100mA. (Topology is just a buck converter and no isolated.)
I assumed LM5019 has 50pF at SW terminal and I calculated how much the peak current for SW terrminal charge up from 0V to 60V using the formula "CV=IT" like the following.
I=CV/T=50pF * 60V / 20ns = 0.15A. This current value is average. So it is 0.30A as peak current. But the acutual peak current is 1.2A. So 0.30A is too small compare with 1.2A.
Do you know what the capacitance value of SW terminal (No.6) of LM5019 is? Is it bigger than 50pF? Is it about 200pF?
Or do you think the 1.2A peak current includes any through current from VIN(No.2) to RTN(No.1)?
Could you please give me your reply or comment? (I'm sorry I can't send you the current waveform taken by the customer at this moment.)
.Your reply would be much appreciated.
Best regards.
Kazuya Nakai.
