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BQ24073: bq24073 / Input current is reduced at low input voltage

Part Number: BQ24073
Other Parts Discussed in Thread: BQ24079T

Hi,

Now I'm checking VIN-DPM function by using EVM and then I found unexpected behavior when EN2=1 and EN1=0. I understand that VIN-DPM is activated when EN2=0 as described in page 8. Actually I can see VIN-DPM function at USB100 and USB500 mode as attached result, but input current is also reduced at EN2=1 and EN1=0 when Vin is gone down. I can't understand why input current reduced like this without VIN-DPM, so can you please explain about this?

Best Regards,

Satoshi / Japan Disty

  • Hello,

    This is normal.

    For this part, when you set EN2=1 and EN1=0. charge current will not change to 0 when VIN<4.5V.

  • Hi Kerry,

    Please explain more why this is normal.Please see my evaluation result at EN2=1 and EN1=0 again.

    The input current start to reduce from 4.7V though it does not go down to 0 suddenly. I'd like to know why it can't keep charge current down to 4.35V (recommended minimum input voltage) though VIN-DPM is not  worked.

    Best Regards,

    Satoshi

  • Hello,

    If you set EN2=1 and EN1=0, will not have VINDPM function. Charge current will not change to 0 when VIN<4.5V.

    if you want VINDPM, you could set other EN1/EN2.

  • Hi Kerry,

    Now I'm asking the mechanism (reason) why charge current is reduced around VIN=4.5V when VINDPM function is disabled. In other words, why bq24073 can't keep charge current at VIN=4.5V that is within recommended Vin range.

    Best Regards,
    Satoshi
  • Hello,

    Below is my test result on EVM. It is normal.

    what's your other test condition? could you test your VILIM or try to replace your IC?

  • Hello,

    Below is my test result on EVM. It is normal.

    ROUT=9.0 OHMS, EN1= LOW, EN2 = HIGH, RILIM=5.23K
    VIN IIN VOUT VILIM
    6.6 283.8 2.484 0.974
    6.3 284.7 2.493 0.974
    5.8 284.8 2.496 0.975
    5.4 284.4 2.493 0.974
    5 284.3 2.494 0.974
    4.5 284.3 2.494 0.974
    4 284.5 2.495 0.974
    3.5 284.5 2.498 0.975

    what's your other test condition? could you test your VILIM or try to replace your IC?

  • Hi Kerry,

    Thank you for sending your test result. But the test condition was not the same with my case. It looks the load was added on SYS pin and the battery voltage was too low. I evaluated again with no load and approx. 4.0V battery as below. Can you try again by referring my result?

    Best Regards,

    Satohi

  • Hello,

    Do you have our EVM? You could test EVM for reference. I think your board and design may be not ideal.

  • Hi Kerry,

    All of my result was measured by using EVM but I'm using bq24079T EVM. My customer also see the same behavior at bq24073 on their test board. Can you try again with the same condition I sent?

    Best Regards,

    Satoshi

  • Hello

    I notices that your 2 test results are different, why?
    I think that the reason for your issue is the voltage drop between VIN and VBAT, because there is a MOS between VIN and VBAT, it will have a voltage drop . please decrease your battery voltage to test.
  • Hi Kerry,

    Here is additional test result as waveform. I changed input voltage continuously. As you can see the input current start to decrease when input voltage down to approx. "Vbat+1V" that is enough higher than Vdo.

    Can you find my email address in profile and contact me directly? I need to respond my customer the reason of this behavior, so I'd like to discuss offline.

    [Evaluated with bq24079T EVM]


    Best Regards,

    Satoshi

  • Hello,

    Could you tell me: 1. is it another question about bq24073? 2. from your waveform, VBAT 3V, VIN decrease to 4V, then IBAT decrease to 0? it is not reasonable, please check your test condition? 3. also, please think about the voltage drop on MOS.
  • Hi Kerry,

    1. I'm using bq24079T for all result in this thread, sorry for confusing.
    2. Regarding input voltage, Vin decreased to 4.35V in my waveform. 4V is out of recommended condition.
    3. Regarding voltage drop on MOS, VDO(IN-OUT) is 475mV(max) and VDO(BAT-OUT) is 100mV(max). I believe that 4.35V input is enough high for 3V battery voltage. Do you not think so?

    Please try again on your bench and send the result. If you don't have EVM, I'll contact app engineer in BMS team directly.

    Best Regards,

    Satoshi

  • Hello,

    could you clear your test condition, I will test at the same condition.
    what's your voltage on VIN pin? this is important, test the voltage near the IC's VIN pin
    please clear your main issue, the main issue now is VIN ? V, then stop charging?
  • Hi Kerry,

    [Test Condition]

    • Start to input 5V and down 0.1V in step as waveform I attached already.
    • There is no system current (SYS is left open).
    • EN2 = High, EN1 = Low

     

    [Main issue]

    • Don't keep the charge current around Vin = 4.35 ~ 4.7V. My understanding is that it should keep it because the recommended minimum input voltage is 4.35V.
    • At this point, battery voltage is approx. 3.0V so I believe that drop out voltage is not the cause of this behavior.

    Best Regards,

    Satoshi