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Original question:

BQ24610: Audible noise and excessive heat

BQ24610: BQ24610: Audible noise

M K
Prodigy 50 points
Part Number: BQ24610

Tool/software:

Hi all!

Let me continue with this thread (cannot continue there, already locked).

Quick reminder: during end stage of charging ("Fastcharge voltage regulation phase"), when current is ramped down, the output voltage (called "Vpwr" on my desing, or "SYSTEM" in datasheet), experience little bumps from 26.4V to 28V. These bumps last about 0.5ms, and are repeated every 3-5ms. These cause audible effect on input ceramic capacitors (C8, C9 on datasheet fig. 20). What is significant, is that these bumps reach voltage that is higher than input power adapter, and obviously than battery voltage. It means this voltage must have been induced by switching action of charger. I can deal with the noise somehow, but again - is it something that can happen with BQ charger, or should I be worried that it is a symptom of underlying design error.

Let me show you screenshots of PH pin voltage (switching node):

Problem overview

detail A

detail B

detail C

, you said, related to noisy capacitors issue:

This might be related to the diode on Vpwr, This should be a MOSFET.

I desoldered the diode between Vbat and Vpwr, but the noise is still there. Waveforms are exactly the same. This issue is encountered only during voltage regulation phase. During current regulation, everything seems fine, and PH waveform looks text-book correct.

Does anyone experienced similar problems with QB charger?

Cheers,

Mateusz Karabela

  • 0
    TI__Mastermind 33111 points

    Hello Mateusz,

    In your schematic it shows a induuctor of 22uF, I reccommend switching to 6.8uF.

    What is the battery voltage?

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    Prodigy 50 points

    Hi Christian,

    I tried 8.2uF (happens to be already on this PCB). I can see it helped somehow - the "bumps" are reduced (from 28V to ~27.5V) but they are still audible. I have 6-in-series cells that I want to charge to 24.6V, and this phenomenon starts to happen about 23V, more or less when the charging current starts to drop from constant 1.05A down.

    The value 22uH seems high, but it was choosen based on datasheet pt. 10.2.1.2.1. like so:

    I assumed charging from completely empty battery, so more or less 18V. Do I get it right?

    Best Regards,

    Mateusz

  • 0 in reply to M K
    TI__Mastermind 33111 points

    Hello Mateusz,

    I'm reviewing this information and will provide feedback after I gather more information.

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    TI__Mastermind 33111 points

    Hello Mateusz,

    After further review, I have another thing to try. Can you add the diode back into the system and place a 10uf capactor after the diode?

    Best Regards,

    Christian.

  • 0
    Prodigy 50 points

    Hello Christian,

    I already tried with and without the diode. Also - there are total 3x10uF capacitors after the diode: one close to BQ, and 2 more bundled with another converters (26/5V and 26/3V3).

  • 0 in reply to M K
    TI__Mastermind 33111 points

    Hello Mateusz,

    Can you provide your updated schematic?

    The schematic I'm looking at does not show the caps.

    I also recommend reviewing the schematic checklist:BQ24610_BQ24650_Schematic_Checklist (58).pdf

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    Prodigy 50 points

    Sure thing, here is updated schematics:

  • 0 in reply to M K
    TI__Mastermind 33111 points

    Hello Mateusz,

    I don't see any capacitance on VBAT.

    M K said:
    I have 6-in-series cells that I want to charge to 24.6V,

    VCharge is set to 24.44V, but you want to charge up to 24.66V?

    Is the inductor still 22uF?

    I recommend following the schematic checklist. 

    Best regards,

    Christian.

  • 0 in reply to Christian Moyer
    Prodigy 50 points

    There is C1115 4u7 capacitance at the right side of schematic, just below schottky diode.

    Yes, I lowered VCharge to 24.44V because I want to charge to 24.44V. I have a feeling that BQ struggles because of something, I don't know what, and I want to make life easier for BQ to operate, eg. by giving it more voltage margin to operate within. And yes, this project is living. Since I am not happy with the results I get with this product, I constantly try to experiment and improve whatever I think needs improving. Because of that, in my posts, you may find that some parameters are not exactly the same as few posts before. So please excuse my inconsistency.

    Yes, the inductor is still 22uH, because of the reasons I described on Jul 29.

    Yes, I did follow the checklist, up to my knowledge and personal experience.

    Cheers,

    Mateusz

  • 0 in reply to M K
    TI__Mastermind 33111 points

    Hello Mateusz,

    These are the recommend capacitor and inductor values, I recommend using the 6.8uH inductor and 20uF output capacitors on VBAT

    Best Regards,

    Christian.

  • 0 in reply to Christian Moyer
    Prodigy 50 points

    Hi Christian,

    I managed to resolve all my problems with BQ:

    - audible noise (this thread)

    - unreliable termination (thread)

    - exploding BQ chips (did not post about it)

    After find my current loop probe, I checked battery current. In full current chaging, it looked nice, just steady level. But as long as Vbat approached Vrechg, it started to look messier and messier:

    And few moments later:

    I had no idea that this current looks so bad. I used TrueRMS meter before, and the RMS value was more or less correct.

    Clearly, there is negative battery current, therefore enegry flows from battery to charger. Datasheet even warns about it in p. 9.3.12 Cycle-by-Cycle Charge Undercurrent Protection:

    This is important to prevent negative inductor current from causing a boost effect in which the input voltage
    increases, as power is transferred from the battery to the input capacitors and leads to an overvoltage stress on
    the VCC node and potentially causes damage to the system.

    Out of curiosity, when hearing noise, I started to manipulate input adapter voltage. When slightly increased, noise seemed to shift up in frequency and be less annoying. In my product I cannot increase input voltage, but I can lower Vreg. I set it to 23,5V. So now, BQ has a margin of 26,5Vadapter - 0,3Vshottky - 23,5Vreg = 2,7V to work with. Now there is practically no noise, and charge termination is accurate and repeatable. And battery current waveform look fine throughout whole charging process. Only downside - I sacrifice a fraction of battery capacity, since I will never charge it to full possible voltage. Anyway, I think datasheet should be more specific about relationship between Vcc and Vreg.

    Another thing: VCC inrush limiting resistor (R17 on fig. 20 in datasheet). Not much is said about it, but in example BOM (table 5) it is rated for 1/4W. Schematic checklist does not mention it's power rating. I had a 63mW resistor there, and replaced it with higher rating. From now on I did not experience any BQ blow outs. Before, I happend from time to time that BQ chip would explode, and R17 resistor was burned. I assumed that resistor burned because of internal short circuit in BQ, but it is possible that it was other way around. Anyway, for anyone interesed: please pay attention to power rating of this component.

    It seems that I got it all sorted out with BQ charger for now. I got a short batch of assembled devices being tested.

    Thanks Christian for your support up to this point.

    Best regards,

    Mateusz