Post Go back to editing

LT3743 - Current shoot through in LTSpice sim?

Hi all, 

I would appreciate a bit of friendly advice. Can you please point me in the right direction? 

I am trying to push the LT3743 to a ~40A solution. I am using it to drive a laser at dc. No PWM. Just 12V to about 40A (Vf is about 1.25V at this current).

I have downloaded and made some adjustments to the LT3743 LTSpice file: the inductor and sense resistor, of course, needed to change. Current at the laser looks good. However, I see the top and bottom side FETs have a significant current transient right when the high-side fet is turned on (HG driven high, LG is low already). It is a current that passes right though both FETs - seemingly from VIN to GND for just a couple of ns . I would appreciate a bit of advice on how to dampen this a bit. I have tried the usual suspects within the circuit, but with no luck. 

It does seem to be FET dependent - I can make it "tolerable" if I switch both FETs to BSC009NE2LS5I, which should be overkill for this circuit. 

Below are two pics showing the transient. I have also attached the .asc files if you are so inclined to look at them.

Thank you!

Jason

Top Fet is BSC080N03LS, Bottom FET is BSC011N03LS 

Top and Bottom FET are BSC009NE2LS5I. 

LT3743_original_40A.asc

LT3743 - BSC009NE2LS5I.asc

  • There is a reference design in the LT3743 datasheet for a 40A circuit - why not start there and then modify that circuit to your requirements?  I mentioned that reference design in this EZ post.  Let's agree on an approach and then we can talk about shoot-through.

    I duplicated that reference design in LTspice and uploaded the .asc file.  The image below shows the circuit and simulation result.  What modification do you want to make to the circuit below so it is better for your requirements?

    LT3743 40A sim ckt and result_1.png

    3743 40A_1.asc