LTC4020 board troubleshoot

[ferbo]

Hi everyone.

I have designed a battery charger using LTC4020 for 12cell lipo batteries. The input range is 40 to 50 volts and the output is set to Max 50.5 and min 40.9.
Max Chargin current is limited to 2.5 A using the sense resistor and later 1A using RNG resistor.

The assembled board seemed to be functioning well. the charging current limited to 1 A and the charging voltage exactly the one I had set and then the Pfet would disconnect the battery after charging completed and the output voltage would be set on 50.5. I didn't try for loads more than 2-3 A but everything looked fine enough for my application.

Then during one of my tests I touched the Nfets to see if they were hot and then suddenly the IC blew out and had a small hole on it. after disconnecting everything I realized the D shotkey diode, The C switch and P-fet for the charging are also gone.

I replaced these plus the LTC4020 and checked everything again for short circuits. then I connected only the battery with no input or output. The same blow out and hole on IC happened again with the new P-fet again being gone. Afterwards I realized my 100 ohm on CSN pin has become 200k instead of 100ohms.

Does anyone have any idea what could be the reason for this?
I am attaching my schematics and layout.

Thank you all.

 

[barry]

Do you know for a fact that the 100 ohm resistor was, in fact, 100 ohms before this all started? I suspect that if it's 200K, the current limiting circuitry will not work, and, thus, you could run excessive current through the MOSFET, Q5.

 

[KlausST]

Hi,

I guess there are layers missing

Klaus

 

[ferbo]

Do you know for a fact that the 100 ohm resistor was, in fact, 100 ohms before this all started? I suspect that if it's 200K, the current limiting circuitry will not work, and, thus, you could run excessive current through the MOSFET, Q5.

Dear Barry ,
Yes I think so because I know for a fact that it was charging at a limited current of exactly 1A before and the input and output currents were normal as well.

--- Updated May 12, 2021 ---

Hi,

I guess there are layers missing

Klaus

Dear Klaus in the file output you can see all the 6 layers separately.But I am also attaching all the layers in one page without the polygons.