Hi,
I'm playing around with a MOSFET H-bridge and IR21844 halfbridge drivers. I'm seeing what I believe are some strange looking gate drive waveform, especially on the high side MOSFET and I'm asking for advice on what might be the cause.
Here's how it looks with no load attached to the bridge:
As you can see there's a "bumb" on the falling edge of the gate drive signal and there's also some ringing on the low side drive signal but that goes away when I attach a load to the output:
Here you can see that the "bumb" has moved to the rising edge instead. The scale for the upper trace (high side gate) is 20V/div in both pictures, the bridge voltage is 24V and the logic supply voltage is 15V. The "bumb" is right on the 24V mark which leads to believe it has something to do with the bootstrap circuit. But what, and why does move from the falling to the rising edge depending on if there's a load attached or not?
Here's part of the schematic, the MOSFETs aren't STW75NF20 but rather STW52NK25Z.
Does anyone know of if there's some "generic" cause for this thing and/or do I need to worry about it or is it even "normal behaviour"? Have I choosen the wrong bootstrap diode (ES1J)? Unsuficiant Cboot (470nF) unsufficiant decoupling on the supply, to large RBoot?
TIA
/Henrik.