Adding an outpiut current clamp to a LTC7803 based Buck?

Hi,

I haven't checked the two datasheets in detail, but have you considered to use the RUN pin for complete shutdown, or manipulating the output/feedback voltage to decrease the peak current?



What is your aimed function / target response?

BR

Thanks yes, i appreciate the foldback feature...but with the tolerances, you could still get an overload of 150% and that woudlnt even kick in.
RUN can shut it down yes. But we want clamping to say 3.2A.

Hi,

cupoftea said:

But we want clamping to say 3.2A.

Click to expand...

isn't that the case if the sense resistor has been chosen properly, to limit the peak current to 3.2 A? Is there an actual use case to allow more current e.g. for a short time?

BR

Thanks, due to the "room" that has to be left for the slope compensation ramp, and the fact that the sense resistor must be undersized, to account for the sense voltage tolerance, the Buck made for 3A output will give significantly more than 3A when overloaded, indeed, significantly more than 3.2A, ....this is why we need the clamp.

Have you considered to increase the switching frequency in case your aimed clamping current is exceeded? The question would be what's the response time if changing the programmable frequency at the FREQ pin.

What is your opearting switching frequency and MODE of operation?

Thanks, its 150kHz and CCM.
Yes its true that if an overload were on the output.....the output current could be regulated down to say 3.2A by reducing the switching frequency.....though i wouldnt be sure if this was the way to go , instead of as already mentioned, playing with the ITH pin or the SS/Track pin.

Ayk, An opamp (acting as an error amplifier) with diode and resistor could be put into the FREQ pin, anode toward pin, but the opamp would then likely need a slightly negative rail in order to be able to pull more current through the resistor, whilst getting into regulation.

The ITH threshold and ranges are defined for each mode.

Why can't they be used to solve your problem?

Hi,

To add a current clamp to the LTC7803 Buck regulator, consider pulling down the ITH pin based on the LTC1871 datasheet suggestion. However, be cautious as the datasheet doesn't explicitly allow it. Since manipulating the "SS/TRACK" pin has no effect, consulting Analog Devices or testing might be needed for a clear approach.
https://www.edaboard.com/threads/adding-an-outpiut-current-clamp-to-a-ltc7803-based-buck.4generative ai09482/

I hope this will help you.

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