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BQ24100: BQ24100RHLR Charger Excess current consumption

Part Number: BQ24100
Other Parts Discussed in Thread: BQ24010,

Hi,

I am using "BQ24100RHLR " battery charger IC in my application. Here I have attached schematic

This circuit is working but i have little problem over power consumption in this IC. When the 3.7V Li-Po battery gets fully charged, charging is stopped and it doesn't deliver current. So as charger IC stops delivering current, Li-Po battery starts discharging for supplying current to the external circuit. After a while, Li-po discharges a little from full charge voltage and battery ic again starts charging.  This should not be the ideal case. Li-Po battery acts as backup so that when Input power(12-15V) is not available, then only Li-Po should start discharging. when external input is present, Li-Po should not get discharged at all(except for little loss). To get it done, later i pulled down TTC(pin7) to ground so that battery charger should deliver current all the time(even when battery gets full) when external input is present. This also worked but i find problem that in this test, battery charger IC consumes around 20mA current all the time when all the loads to the battery charger is isolated. I mean isolating 3.3V regulator input from charger output and not connecting Li-Po to the battery charger output. This 20mA current at no load is too much current consumption as the 12-15V input comes from another Lead acid battery. So at this much current consumption in the battery charger ic itself will lead to major dron and will soon discharge the lead acid battery..

  • Hi Kumar,

    The IC is operating as expected. It is a non-powerpath device, which does not have a separate rail for system. When you connect the system directly to the battery, this is what happens. If you would like to have the converter run as soon as you have the load connected, you could use a NFET from TTC to GND and activate it when you have a load connected (either controlled by GPIO or manually using a mechanical switch). This will disable termination while having the load connected and enable termination when there is no load.

    Regards,
    Steven
  • Hi Steven,
    Thanks for your suggestion. after pulling the TCC pin low, its able to deliver power even when battery is fully charged. But i have another big concern for power consumption. This IC consumes around 20mA@12V input when programmed for 300mA output even at no load condition. Do you think, this consumption is expected? 20mA consumption is low for no doubt but our concern is the source of this input is another lead acid battery. Basically its automotive application where the system would run from the vehicle battery. vehicle may be parked for more time(maybe in several days) and hence there won't be charging of the lead acid battery for those time. if this charger ic takes 20mA current then vehicle battery would die very soon and our system would not run for long time. If you have any suggestion then please suggest me even for any other part but it should be highly efficient. FYI i would like to tell you that we are going for production. Our old design was using "BQ24010DRCR" but now we need to get with input voltage in the range 16-20V operation ideal being 12-16V input range. Please note that we had serious issue with BQ24010DRCR  over temperature as this ic was getting heated up to 85 degree celcius at normal 350-450mA programmed load.
    Regards
    kumar

  • Hi Kumar,

    Just to quickly note, the bq24010 may have been overheating due to layout. I would see if the thermal pad was properly connected to a ground plane to dissipate heat.

    Does the bq24100 have this 20mA consumption when TTC is not pulled low? I'm thinking that because termination is disabled, the charger never stops charging, and the 20mA consumption is because there is no termination. This is why I suggested some sort of switch (NFET or mechanical switch) to only pull TTC down when the load is connected.

    Regards,
    Steven
  • Hi Steven,

    bq24010 IC was overheating due to its input voltage. I was giving input voltage as 12V and as per the datasheet of this ic, it was expected behavior as the heat dissipation is proportional to the input voltage applied. Later i have changed to 5V input voltage and it works fine(normal temperature).

    Q. Does the bq24100 have this 20mA consumption when TTC is not pulled low?

    Yes i get this 20mA@12V continuous current when TTC pin is pulled low when battery is fully charged and even when charger is not loaded(external load disconnected).

    Regards

    kumar

  • Hi Kumar,

    I understand what happened with the bq24010, the input voltage is directly proportional to the heat loss on the linear regulator.

    As for the bq24100, yes, it looks like a switch on the TTC is necessary to reduce current consumption when battery is fully charged and there is no system load. TTC switch should pull low GND when system load is connected, and disconnect when there is no system load.

    Regards,
    Steven