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BQ24167 hum noise

raj kumar2
Prodigy 110 points
Other Parts Discussed in Thread: BQ24167, TPS2500

HI,

I am using BQ24167RGET dual input charge in my design.

In both charging & discharging phase i am hearing hum sound.

I am suspecting the noise is generated by the inductor.

As per reference design i am using "SPM4012T-1R5M" inductor.

Inductor :-  http://www.digikey.com/product-detail/en/SPM4012T-1R5M/445-15778-1-ND/4328074

Current limit setup:-

Maximum AC charge current limit is 1.5A.

Maximum USB charge current limit is 900mA.

Even for some lower current i am hearing hum sound.

  • 0
    TI__Guru**** 157141 points

    Ceramic capacitors are known for their piezoelectric vibration that can result in the PCB, acting as a diaphragm, to buzz or hum.  Two ways to reduce the buzz/num: replace a big footprint capacitor with several smaller ones in parallel or you can cut slits in the PCB on each side of the capacitor. 

  • 0 in reply to Jeff F
    Prodigy 110 points

    Hi Jeff F,

    Thanks for your replay.

    For your reference here i am attaching the sch & layout placement images.

    I am worried that replacing big caps with several smaller cap will affect the system performance?

    Also it is difficult to cut the PCB.

    Additional info:- All caps in charger blocks are X7R cap except 4.7uF/25V C9&C10 those are X5R cap.

    Will it be the problem?

    Images:-

  • 0 in reply to raj kumar2
    TI__Guru**** 157141 points

    Try replacing the two 4.7uF capacitors with 2 x 2.2uF in parallel in a smaller footprint (same ratings) and the 47uF with either 2 x 22uF in smaller footprint (same ratings).  If the hum changes, then the capacitors are the issue.

  • 0 in reply to Jeff F
    Prodigy 110 points

    Hi Jeff,

    I am using BQ24167 dual input charger IC & TPS2500 USB Boost converter in my charger design.

    I am able to hear HUM sound from the system.(Mostly near Input section of TPS2500 )

    Block Diagram:- 

    Circuit :-

    While probing battery voltage (when Hum sound is resent) i am able to see max 560mV fluctuation on bat+.

    Plot:-

    Battery Signal levels for Samsung Galexy mobile load are,

    Battery Spec:- 3.7V / 3Ahr Li-ion battery.

    Bat Voltage = 3.59V 

    Load current =510mA (To mobile)

    Noise Amplitude=440mV

    Noise Frequency= 4.0KHz (Frequency of the signal will vary depends on Load current & battery % based on this I am able to here different hum sound ).

     

    TO Reduce Noise :-

    I tried to change TPS2500 inductor from 3.3uH to 2.2uH. --> Still noise is present.

    I added 150uF bypass cap on Battery node.--> Noise ampletude reduced to half.(but still low sound noise the present)

    Pls help to solve this issue.

    Thanks in advance.

     

    Regards

    Raj

  • 0 in reply to raj kumar2
    TI__Guru**** 157141 points

    The noise is likely due to the ceramic capacitors.  Ceramic capacitors have an undesirable piezoelectric effect that causes them to vibrate with the ripple voltage across them.  The PCB board acts like the diaphragm of a speaker.  Replacing one large footprint capacitor with several smaller capacitors in series can help.  Cutting slits in the PCB on each side of the capacitor can help.  Replacing the ceramic capacitor with an equivalently low ESR non-ceramic can help.

    But, first we need to figure out why you have such large ripple on BAT+.  Is your load on SYS pulsing at that frequency?  Is the input current to the bq24167 pulsing due to the input source collapsing?  I see that one of your source's is a solar panel?  Does this happen only when on solar power?  When using solar or other high impedance input source, it is generally recommended to use the input with the adjustable VDPM feature, set to the panel's maximum power point voltage, so that the charger does not crash the solar power by pulling too much current from it.

  • 0 in reply to Jeff F
    Prodigy 110 points

    Hi Jeff F,

    Thanks for your kind replay.

    My comments:-

    Replacing one large footprint capacitor with several smaller capacitors in series can help.

    1210 is the biggest size ceramic cap (C4,C9 & C10) in this block rest of them are 0805 package only.

    Do i have to replace 0805 with 0603?

    or can i directly use same size tantalum cap ? (This doesn't require PCB redesign)

    C3 is C2917 size 150uF tantalum cap on load side of TPS2500.

    If you have any suggestion to remove any cap from sch pls let me know it.

    Is your load on SYS pulsing at that frequency?

    Yes, I have a DC-DC Boost converter (TPS2500) on my SYS load. (It’s switching freq is 1MHz)

    Which boosts the battery voltage to 5V & I am using that to charge mobile.

    Is the input current to the bq24167 pulsing due to the input source collapsing?  I see that one of your source's is a solar panel?  Does this happen only when on solar power?  When using solar or other high impedance input source, it is generally recommended to use the input with the adjustable VDPM feature, set to the panel's maximum power point voltage, so that the charger does not crash the solar power by pulling too much current from it.

    One of my inputs is solar panel. My solar panel have internal circuit & DC-DC converter & which gives maximum output of 5V 900mA.There is no ripples on BQ24167’s input.

    While doing this experiment I didn’t give any i/p source to BQ24167. (No solar, No AC Adapter)

    This means I am getting ripples on battery discharge cycle.

    Where can I get more detail about “adjustable VDPM feature”?


    Thanks & Regards

    Raj

    raj@tanmic.co.in

  • 0 in reply to raj kumar2
    TI__Guru**** 157141 points

    The bq24167 was designed for use with very low ESR ceramic capacitors.  If you can change to low ESR tantalum, there should not be an issue.

    I am still still puzzled by the 4kHz pulsing.  Is the voltage at BAT dipping below 2.5V during discharge?

    There is brief section in the 167 datasheet above VINDPM.  Below is a link to an article I wrote that includes a description on VINDPM at the end.

    http://www.ti.com/lit/an/slyt569/slyt569.pdf