LTC4162EUFD-LAD charger (12V/2.5 A) problem

Hello,

I am developping a charging board for lithium battery (2 cells) based on LTC4162EUFD-LAD with a charger 12V/2.5A. I made some samples and all working fine . Now we produce the pre-release series and one problem comes out ( identical components and PCB layout). If we try to charge the battery using the charger 12V/2.5 A the LTC4162 fails battery detection ( repeat battery detection every 30 secods as datasheet describes). Instead with a charger 15V/2A all works fine. Do you have some suggestions? I mean where  should I check to verify why battery detection fail.

Thank you.

Gaetano

Parents
  • 0
    •  Analog Employees 
    on Sep 23, 2020 5:49 PM 3 months ago

    Hi Gaetano,

    Can you send a schematic?

    Take a look at the voltage on the battery node with no battery connected but input voltage present. Every 30 sec, you should see the voltage pop up to the battery float voltage. Can you capture a scope plot of that?

    Also, what does that event look like with the battery connected?

    Regards,

    Zack

Reply
  • 0
    •  Analog Employees 
    on Sep 23, 2020 5:49 PM 3 months ago

    Hi Gaetano,

    Can you send a schematic?

    Take a look at the voltage on the battery node with no battery connected but input voltage present. Every 30 sec, you should see the voltage pop up to the battery float voltage. Can you capture a scope plot of that?

    Also, what does that event look like with the battery connected?

    Regards,

    Zack

Children
  • Hi Zack,

    thank you for your reply.  I found a strange behaviour.

    My current set-up is:

    • Icharge = 1 A ( max current for recharging battery)
    • Iin=1.5 A (max current requested to the charger)
    • Charger is 12V/2.5A

    If I decrease the Icharge to 0.7 A  almost all boards work fine ( using 12 V/2.5A charger) but one of them needs to reduce the Icharge to 0.5 A. That's really strange. Moreover if I move charger and battery to the first samples all working fine with my original current set-up (charge = 1 A ) . It looks like an unwanted current absorption . What do you think? Wrong way to soldered LTC4162 or maybe tollerance of passive components?

    I wasn't in office today so I'll send you the picture of scope tomorrow.

    Regards.

    Gaetano

     
  • 0
    •  Analog Employees 
    on Sep 24, 2020 9:45 PM 3 months ago in reply to gaetano

    Hi Gaetano,

    Hmm, failure at higher currents is usually indicative of a layout issue, though that may not be the case here. Regardless, can you send your layout?

    Regards,

    Zack

  • Hi Zack,

    attached you can find the layout. Just to recap. We produced 10 boards and all work fine with the follow configuration ( I'll call it whished configuration):

    • Icharge =1 A, Ilimit=1.5 A
    • charger 12V/2.5A

    We carried out a lot of test and no problem like this came out. After that we produced 30 identical boards( layout, BOM , etc.) and I saw these strange behaviours. Moreover 23 boards work fine with our "whished configuration" and 7 of them need Icharge lower ( Icharge =0.5 A). These seven boards work fine with our "whished configuration"but  if I use a battery not completely descharged ( 8 Volt , our battery is 2 cells ). Components are not soldered by hands and PCBs are made at the same time.

    I can reduce Icharge( it' isn't critical ) but I want to  understand where is/are the faults (production, project limitation,etc).

    Reagrds,

    Gaetano

  • 0
    •  Analog Employees 
    on Oct 1, 2020 4:53 PM 3 months ago in reply to gaetano

    Hi Gaetano,

    Is this a two-layer board? It is possible to route this on two layers but there is more room for error. What temperature does it reach?

    Also, I can't really see the bottom layer, but is there a good path from the GND side of the VCC2P5 cap back to the IC GND pad? Can you send the bottom layer as well?

    Regards,

    Zack

  • Hi Zack,

    yes the board is two layers. IC reaches the follow temperature:

    • when Icharge=1 A during costant current phase temperature is 72 °C
    • when Icharge=0.5 A during costant current phase temperature is 62 °C
    • of course during costant voltage phase decrease until 40 °C
    • fault occurs at start so I think it isnt temperature the problem

    Can you send me something about the layout guidelines ( link or document)?

    If you give me an email I'll send you the gerber files if needed.

    I still don't understand why  , when  battery is really descharged , charger 15V/2A works fine instead charger 12V/2.5 A not .

    Do you have any idea?

    Regards,

    Gaetano