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Original question:

BQ24075: Charging Issue

BQ24075: BQ24075 does not start re-charge unless USB is removed and replaced

Warren Muir
Intellectual 525 points
Part Number: BQ24075


Hi Power Management Gurus

A previous post of mine on the BQ24075 refers. The only way I managed to solve the problem was by connecting a 10k resistor between NTC and the supply. See schematic below:-

I am now challenged with a new issue, and wonder if anyone can assist. The battery charges up to 100% and then obviously stops as expected. My application draws about 100mA in a certain mode from the battery. The charger does not seem to turn on unless the USB is removed and re-inserted. Is there a way to kick start the charge without having to remove the USB? 

  • 0
    TI__Mastermind 23410 points

    Hi,

    Warren Muir said:
    The charger does not seem to turn on unless the USB is removed and re-inserted

    Is this based on the /CHG output? The /CHG indicator will only be low for the first charge cycle after power insertion at the IN pin. Once the battery has been fully charged, the /CHG output will pull high to indicate not charging. If the battery voltage falls below the recharge threshold, the battery should still be charging but the /CHG will not indicate that. 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Intellectual 525 points

    Thanks for the response Anthony.

    Yes, I use the /CHG pin to indicate charging on an LCD, so this answers my query to an extent.

    Is there any other way to detect charging, apart from monitoring battery voltage with an A-to-D?

    What is the charging threshold on the BQ24075 - datasheet indicates Vrch = Vbat(reg) - 100mV, and Vbat(reg) is 4V2 for the '75, so it should start recharging at 4V1. However, on our application, the battery does not seem to recharge until well below 3V7. Our challenge is that our application is pulsing 100mA and we have a msp430 on a 3V3 reg fed by Vbat, so when Vbat falls below 3V5, a pulse sometimes causes the micro to reset.

  • 0 in reply to Warren Muir
    TI__Mastermind 23410 points

    Hi Warren,

    Warren Muir said:
    Is there any other way to detect charging, apart from monitoring battery voltage with an A-to-D?

    You can use the voltage on the ISET pin to monitor charge current. The voltage can be used by the host (in this case the MSP430?) to calculate the current sourced into the battery

    Warren Muir said:
    However, on our application, the battery does not seem to recharge until well below 3V7

    Are you measuring the current going into the battery? How are you determining that the battery doesn't seem to recharge until below 3V7? 

    Warren Muir said:
    Our challenge is that our application is pulsing 100mA and we have a msp430 on a 3V3 reg fed by Vbat, so when Vbat falls below 3V5, a pulse sometimes causes the micro to reset.

    Can you show a snippet of this portion of the schematic? Are you saying something else is also being connected to the battery and regulating to 3V3? 

  • 0 in reply to Anthony P Pham
    Intellectual 525 points

    Thanks for your response Anthony, and apologies for my delayed feedback - I have been out of the office.

    1. I have an OpAmp on ISet feeding an A-to-D to the host, so will use this to confirm charging

    2. I am measuring the current into the battery - charge current is set to 360mA and I measure 356mA, so happy that this is working well  

    3. Battery charging seems to stall after the battery charge reaches 100%. Worst case draw on Vout is approx 200mA, so this theoretically exceeds the 500mA from source when simultaneous charge current is 360mA. However, when charging stalls, the total draw from the source will be proportional equivalent to 200mA from 5V-USB. I have left units connected to a PC USB and/or a wall charger for a few hours but they still won't start charging again. 

    4. Vout supplies a LD2981 that supplies 3v3 to the MSP430 and Vbat supplies a TI boost converter that supplies a TI H-Bridge - see snippets below - not sure if you can see these clearly, but can private message them in pdf if necessary.

  • 0 in reply to Warren Muir
    Intellectual 525 points

    Hi Anthony

    Just a point to consider. As per previous correspondence with Raheem, I could not get charging to initiate until I connected a pull-up on the Tprg (NTC) pin - see schematic below. Could this be causing the issue? If so, any suggestions on solving it. Also, does TI have a USB charger that can source higher current from the USB.

     

  • 0 in reply to Warren Muir
    TI__Mastermind 23410 points

    Hi Warren,

    The direct connection with the battery to the resonant output driver could be the culprit here. As it also consumes power from the battery, the current going into the battery when it meets the recharge threshold is low compared to the power draw by the driver. 

    Does this behavior of not charging occur with the resonant driver?

    Warren Muir said:
    I could not get charging to initiate until I connected a pull-up on the Tprg (NTC) pin - see schematic below.

    I looked over the thread with Raheem. Did you receive an EVM and did it work when you tested the IC on the EVM? Do you also see the TS voltage at 0V when the battery falls below the recharge threshold after a complete charge cycle?

    Best regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Intellectual 525 points

    Hi Anthony

    1. The issue occurs when the boost converter and H-Bridge are active and drawing 200mA or more from the battery - 200mA seems to be the threshold. Anything lower seems to be fine. The issue is that after the boost converter and H-Bridge are turned off, battery charging does not seem to restart until I remove and re-insert the USB.

    2. I never received the EVM from Raheem. I followed up with our local agent Rodney Farrow, but he could not track the package for some reason.

    3. I have not checked the voltage at TS for the issue in item 1 above - will confirm tomorrow.

  • 0 in reply to Warren Muir
    TI__Mastermind 23410 points

    Hi Warren,

    Thank you for the information!

    Warren Muir said:
    The issue is that after the boost converter and H-Bridge are turned off, battery charging does not seem to restart until I remove and re-insert the USB.

    Interesting! Just to satisfy my curiosity, does this occur if the boost converter and H-bridge are not connected? 

    Warren Muir said:
    I never received the EVM from Raheem. I followed up with our local agent Rodney Farrow, but he could not track the package for some reason.

    Let me also reach out to Rodney and see what we can do about this. 

    Warren Muir said:
    I have not checked the voltage at TS for the issue in item 1 above - will confirm tomorrow.

    I appreciate the update, looking forward to the new data. 

    Best Regards,

    Anthony Pham