LTC7862 Current Threshold

The way I have set up the sense pins in LTSpice for reference

Hi Beth,

I noticed that sense resistor is placed right before the inductor (L1).  It should be placed after the inductor. See diagram below from the datasheet.

Please fix the connection and run the simulation again. 

Did you see switching behavior when it trips near 30A? If so, it is due to overhead inductor ripple current on top of the average output current.  In this case, you will have to take into account of the inductor ripple current in your design calculation.  See page 15 of the datasheet for guidance.

Hi, thank you for your response and the advice on the inductor placement. I have since changed the set to the following:

I understand your explanation of the inductor ripple during regulation. For example, during an overvoltage when the FETs are switching causing the inductor current to ripple. The peak of this current reaches about 48A before the overcurrent condition kicks in, which (allowing for tolerances) is what I would expect after your explanation and that of the datasheet.

However, if the situation occurs during normal operation (ie no switching) and the current increases, I'm unsure as to why it would start to regulate when the output current (and inductor current) are roughly 30A.

The simulation above shows this. As the current increases from 25A, at 30A regulation starts to take place and a fault condition is flagged (light blue trace shows the warning pin which is pulled low). I can see no reason for this as the voltage feedback is below it's threshold and the current sense voltage is at roughly 30.9mV (below the 50mV threshold). If you are able to shed some light on this that would be much appreciated.

For the simulation:

Green= Input voltage; Dark blue= output voltage; Red= Inductor current; Pink = output current; Light blue = warning pin

Hi Beth,

Could you upload the LTspice file?  or show a picture of full schematic?  I just want to replicate the problem here and see what's gong on.

What's the design output clamp is set at?

LTC7862 surge stopper with RB.asc

Are you meaning the maximum output voltage? If so, it set at roughly 39V

Hi Beth,

It seems maximum current sense threshold is not set properly in the LTspice model.  Thanks for reporting this problem.  I will contact our LTspice team to fix this issue.  Make sure you update the LTspice program often.

Hİ, Did you fix the current limit threshold problem ? 

Hi Gene, 

It is still not working properly in the LTspice. I checked the lastest version.

Hi,

Thank you for your patience. We apologize for the long delay before this has been started to be addressed.

The issue on LTC7862 Current threshold has already got the attention of the LTspice team.
A model update is already on its way.
An internal process just needs to be completed before the updated model will be made available in the LTspice library.

Please perform a Sync Release to update your LTspice library in a week or two.
We will also monitor the progress of this until your concern on this particular issue in LTC7862 is resolved.

Hi KAYDIN556,

An updated LTC7862 model is now available in LTspice library.
Please perform a Sync Release to update your library.

Here's a basic test I did. It shows that the Vsense max is set at 50mV.