Electronics > Projects, Designs, and Technical Stuff
Synchronous Buck IC with Internal Power Switches - failing
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Systemtek:
It is designed to be supplied from the output of another DC/DC converter with a large output capacitance. I don't yet know what the DV/DT of the output of the supplying converter is when it starts up.
Jeroen3:
Who said this works with lion batteries? The thing is made for lead batteries. Specifically:

--- Quote ---The switching charger can
charge 6V, 12V, 18V or 24V lead-acid batteries.
--- End quote ---

A 24V system absolute max voltage is often 33.6V. So the 35V maximum voltage is for fault conditions.
I'd expect intended operating voltage of this chip to be 14 or 28 Vdc.
Systemtek:

--- Quote ---Who said this works with lion batteries? The thing is made for lead batteries. Specifically:
Quote
The switching charger can
charge 6V, 12V, 18V or 24V lead-acid batteries.

A 24V system absolute max voltage is often 33.6V. So the 35V maximum voltage is for fault conditions.
I'd expect intended operating voltage of this chip to be 14 or 28 Vdc.

--- End quote ---

Apologies I meant to link the datasheet for the li-ion/lifepo4 model. I ordered this exact part number - LTC4162EUFD-LAD#PB. From this page and datasheet.https://www.mouser.co.uk/ProductDetail/584-4162EUFDLADPB
nctnico:

--- Quote from: Systemtek on November 24, 2019, 07:30:03 pm ---Thanks for your replies.

So lets say I can design an input filter that is optimized for stopping the input voltage ringing/overshooting. Is it still the case that when charging the 8 Li-ion cells it is designed for it might just keep failing?

The fully charged voltage of the stack is 33.6V it doesn't allow me to drop the input voltage much lower at all. There also isn't enough of a margin there to use a TVS diode that wouldn't have too high of a leakage current as far as I can tell. 

I can't find another 8 cell solution as good and feature rich as this one so I'd hate to have to give it up.

--- End quote ---
I'm afraid you have to. I ran into a similar problem with one of my own designs but fortunately I could set the supply voltage lower and use a TVS diode to keep the device within limits. The absolute maximum rating doesn't have any margin on it.
Systemtek:
Maybe it's worth just adding a cheapy high ESR electrolytic across the input filter ceramic and starting it up with a current limit to create a slower rising edge while monitoring Vin at the pins of the IC and switch node with a scope. I could run it at a lower voltage but no so much as to voltage coefficients of the ceramics don't throw out the filter cap tuning and see if I can work it out by experimentation.
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