DC512B not working

Hi,

I'm trying to debug the DC512B (with the LTC4100).

I prepared the setup:

  • Configured the board for a 3S with ILM 3A
  • Connected the power supply to DCin with 16V and 3.2Amp. 
  • Connected a thermistor of 10k on the "T" plug and the battery between Bat and GND

At the beginning I also connected the SCL and SDA to the smart battery pin. I checked with the oscilloscope that the 0x12 commands (current and voltage) was available on the bus.

After turned on the power supply, the ACP led switched on and also the CHGEN.

But I can ear very clearly a switching noise coming from the board and I saw the power supply current demanding completely not constant.

In the second stage I unconnected the SDA and SCL and I tried a “dry run” also with a load of about 50 ohm connected, but the behaviour was the same. (I read that the charger can work also without configuration)

I think that there is something of wrong, but I cannot understand what it is.

I attach the screenshot form the oscilloscope, where you can see the voltage on the battery (blue), the yellow and purple are the two pins of the coil.

Overview:

 :

Zoom:

Thnaks for the support

  • 0
    •  Analog Employees 
    on Mar 9, 2020 7:34 PM 7 months ago

    Hi Fabrizio,

    The switching looks normal. Does it seem to be receiving the current that it is requesting?

    The charging seems to stop after a short time. Did you stop the charging or does that keep happening repeatedly? Try increasing your input power - more voltage or more current. You may be power-limited at startup.

    If you have a current probe, maybe take a look at the battery current.

    Regards,

    Zack

  • Hi Zack,

    thanks for the answer.

    Today I retried with a new test, following your suggestion and in that conditions:

    • 3S battery connected and already charged at 78%. The battery requires less than 1 A in that condition. Its voltage was about 10.70v
    • No load connected on the DC512B
    • ILIM set to 3A, VLIM 3CELL
    • No SMBUS connected
    • Thermistor of 10K connected.
    • Power Supply increased from 15 to 24V, 3.2 A


    ACP, CHGEN high.

    The behaviour is the same of yesterday. I can hear switching glitches from the coil, I can see periodic absorption on the power supply (which didn't enter in limitation, only 3-5 W of peak achieved) .

    I never stopped the charging but it is happening repeatedly.
    I also tried to reduce the cable length, but nothing is changed.

    I have not the current probe. Can you suggest other checks?

  • 0
    •  Analog Employees 
    on Mar 11, 2020 4:52 PM 7 months ago in reply to Fabrizio R.

    Hi Fabrizio,

    Sure, a couple more things to check.

    Take a look at the INFET signal. Is it steady ON or is it turning off with this function?

    Check on SDA/SCL while this happens, is there communication that stops the charging?

    Regards,
    Zack

  • Hi Zack,

    today I tried to make the new test that you suggested, but after switched on the setup, the transistor Q11 burned.

    I suppose the same problem of this topic: 

    https://ez.analog.com/power/f/q-a/116863/ltc4100-evaluation-board-q11-fet-issue/348352#348352

  • 0
    •  Analog Employees 
    on Mar 12, 2020 7:14 PM 7 months ago in reply to Fabrizio R.

    Hi Fabrizio,

    It could just be a hot-swapping issue with a high-voltage battery. Try replacing the FET and adding a 10k pull-down resistor on the gate.

    More info in this blurb:

    When a battery is inserted with no other supply present, the battery will pull up the BAT and CSP
    pins and will begin to charge the inductor which also pulls up the SW node. The CLP and CLN pins
    will also be pulled up via the body diode of the top FET. The exact speed and order of this
    sequence depends on many factors largely influenced by parasitics.
    During these events, the BGATE pin is not driven by the IC (high or low). After a hot plug event, the
    IC typically requires about a millisecond or so to take active control of BGATE. Without an active
    pull-down, SW pull-up energy couples through the bottom FET Miller capacitance, turning on the
    FET if its threshold is exceeded. If the bottom FET turns on for an extended period of time, it can be
    destroyed by the simultaneous combination of Vds and Ids.
    We have been unable to replicate FET failure in the lab, but we have been able to initiate bottom
    FET conduction via the capacitive coupling discussed above. Note — the likelihood of turning on the
    bottom FET depends on many factors including FET threshold and battery voltage. Given the ratio
    of Miller capacitance to gate capacitance, it is unlikely that battery voltages below about 10V can
    cause this problem. Therefore, 1-cell and 2-cell Li-ion applications are probably safe.

    Solution: A simple solution to this issue is to ground the BGATE pin with a resistor. 10k seems to
    work well and has minimal impact on switcher efficiency.

    Regards,

    Zack