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LTC3114 devices failing in application according to datasheet

joachimbaumm

LTC3114 devices failing in application taken from datasheet

Customer Kuhnt has an issue with LTC3114EFE.

About 30 devices of 40 in total were damaged.

They use an application like the lead acid battery charger on page 29 of the data

sheet, with the optional diode.

The deviations from the datasheet schematics is

- they have a 24V battery instead of 12V

- hence the output voltage is set to 27,5V

- with a prog-resistor of 100k they set a current limit of 250mA,

- they have a regulated input voltage of 24V

- they use a 10uH inductor (Bourns SRR0745A-100M).

The layout of the four layer PCB is based on the recommendation on page

 18 of the data sheet. There is a shottky diode between the regulator

 output and the battery to prevent reverse current.

 -> Damaged parts have a shortcut either from SW1 to ground or from SW2 to ground.

 The application has also been simulated with LTspice and did not show any fault.

  • 0
    •  Analog Employees 
    on Jan 23, 2018 8:32 PM

    Thanks for your question.  We will review your application and follow up with suggestions.

  • 0 on Feb 20, 2018 1:01 AM

    I have 2 x same problem with same part.

    Application 1, a 4V Power Supply

    Using component values from 5V regulator circuit in app note

    LTC3114 is programmed to 4V output.instead of 5V with feed back resistors

    25% of LTC3114 get hot and fail on start up when 12V applied to input

    25% of LTC3114 catastrophically fail with burning when 30V is applied to input

    Application 2, a 12V Power Supply

    Using component values from 12V regulator circuit in app note

    25% of LTC3114 get hot and fail on start up when 30V is applied to input. 12V on input no problem.

    In both cases the problem happens on start up when the input voltage is higher than output voltage (buck mode).

    When input voltage applied is less than the programmed output voltage (boost mode) the failure doesn't happen. 

    In both cases if failure on start up does not happen the circuits are reliable.

    Advice is appreciated.

  • 0
    •  Analog Employees 
    on Feb 21, 2018 12:37 AM

    I would suggest reviewing the datasheet for layout and design suggestions as well as looking at the demo board design (DC1821B).  The demo board design files are available on www.linear.com.

     

    Since the layout and component placement are critical in these designs the demo board can provide an example of a working design.  It can also be helpful to obtain the demo board and compare the working circuit’s waveforms to your design.

     

    If you continue to experience issues it’s best to contact a local Field Applications Engineer so that operating parameters, waveforms, layout and circuit design can be reviewed. 

  • 0 on Feb 21, 2018 2:58 AM

    Thanks for suggestion. It would be interesting to see if the demo board is different to mine. I'm using 4 layer PCB with ground plane under the LTC3114 and very short tracks. Meantime I have temporarily fixed the problem by clamping the VC pin low at power on time for one second followed by a 1 second turn on time ramp using a FET and RC. No failures at all since then. I dont know if temporary connection of VC to GND is a problem.

  • 0
    •  Analog Employees 
    on Aug 2, 2018 4:01 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin