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TPS65131: Noise issue on dual DC/DC converter

HXC
Prodigy 20 points
Part Number: TPS65131

Tool/software:

Hi everyone!

I used the TPS65131 in my project to have a dual power supply following the application notes and the routing of the evaluation board. When I power the board I hear an annoying buzz. I checked the schematic, PCB, power supplies and everything else but I didn't find any particular inconsistencies. If I put my finger on C70/R133 the noise fades a lot becoming almost imperceptible.

Any ideas on what it could be? Incorrect sizing? Incorrect routing? What tests can I do to understand where I'm going wrong? The integrated circuit seems to work correctly with the correct input and output voltages.

Below I post the electric diagram, the layout and the BOM.

Thanks to anyone who can help me.

Item Quantity Reference Description Value Manufacturer PartNumber
______________________________________________
1 1 C65 Multilayer Ceramic Capacitors MLCC - SMD/SMT 220 nF 6.3 VDC 220 nF 0603 X5R 220nF KYOCERA AVX 06036D224KAT2A
2 1 C66 Multilayer Ceramic Capacitors MLCC - SMD/SMT 7.5 pF 50 VDC 0.1 pF 0603 C0G (NP0) 7.5pF Murata GRM1885C1H7R5BA01D
3 1 C67 Condensatore ceramico multistrato MLCC, 0603 (1608M), 4.7nF, ±5%, 50V cc, SMD, C0G 4.7nF Murata GRM1885C1H472JA01D
4 2 C68,C71 COND CERAM SMD1206 4.7UF 50V 10% 4.7uF SAMSUNG CL31B475KBHNNNE
5 1 C69 CONDENSATORE MLCC 10nF ±10% 25Vdc C0G(NP0) SMD0603 10nF KEMET C0603X103K3GECTU
6 1 C70 MLCC - SMD/SMT 0805 6,8PF 50VOLTS X7R 5% 6.8pF VISHAY VJ0805A6R8BXACW1BC
7 3 C72,C164,C166 COND CER SMD 0603 0.1UF 10% 16VOLTS 0.1uF MURATA GRM188R71C104KA01D
8 2 C73,C74 4.7 µF, ceramic, 6.3 V, X5R 4.7uF AVX 08056D475KAT2A
9 5 C163,C165,C167,C168,C169 COND CERAM 10UF 25V 10% X7R SMD1206 10uF AVX 12063C106KAT2A
10 2 D12,D13 Schottky Diodes & Rectifiers 1A 20V Low Vf MBR120LSFT3G onsemi MBR120LSFT3G
11 2 L3,L4 Power Inductors - SMD 4.7uH 2A 20% 6.3x6.3mm SMD B82462G EPCOS / TDK B82462G4472M
12 2 L9,L10 Perline di ferrite 400 mA 25 % IMP=1 kOhms Shielded SMD/SMT DCR=300 mOhms Ferrite Bead Pulse Electronics BBGK00201209102Y00
13 1 Q3 MOSFET, P-channel, 12 V, 4 A, Si2323DS Vishay Si2323DS
14 1 R21 THICK FILM CHIP RESISTOR  121K 1% 0.1W 0603 SIZE 121k Vishay CRCW0603121KFKEA
15 2 R22,R23 SMD 1/4W 1M OHMS 0.05% 1206 10PPM 1M SUSUMU RG3216N-1004-W-T1
16 1 R24 Thin Film Resistors - SMD RP 1J 0.166W 130K 0.1% 25PPM 130k TE Connectivity / Holsworthy RP73PF1J130KBTDF
17 1 R25 Resistore SMD Vishay Film sottile, 100O, 0603 (1608M), ±0.1%, 0.100W R100 YAGEO RT0603BRC07100RL
18 3 R117,R118,R130 RESISTORE FILM SPESSO 0R 5% 1/10W SMD0603 0R Vishay Draloric CR0603AJ/-000ELF
19 2 R132,R133 THICK FILM CHIP RESISTOR  51.1K 1% 0.1W 0603 SIZE 51.1k Vishay CRCW060351K1FKEA
20 1 U18 x Dual, Positive and Negative Output DC-DC Converter TPS65131 Texas Instruments TPS65131RGER
  • 0
    TI__Mastermind 30761 points

    Dear Sir,

    Our expert Patrick will get back to you early next week. Thanks for your understanding!

    BRs

    Lucia

  • 0
    TI__Mastermind 34840 points

    Hi HXC,

    Could you please capture the waveforms of VPOS and INP?

    Seems you only added one 4.7uF as the output cap of VPOS which might be too small, you can try adding more capacitance as well.

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Prodigy 20 points

    Hi Patrick,
    thanks for your feedback.

    Attached you'll find captures of
    -INP as design
    -VPOS as design
    -VPOS + 4x10uF X7R

    Adding capacitors on top of C71 relaxed the ripple frequency but didn't changed at all the audible noise.

    More test were given adding capacitance (one change at time) on:
    - C70 +6.8nF
    - C74 +10uF
    - C163 +10uF
    but, again, nothing changed.

    Are there any more test I can perform to spot the issue?


    Thanks,

    Salvatore

    INP

    INP

    VPOS

    VPOS

    VPOS + 40uF

    VPOS + 40uF

  • 0 in reply to HXC
    TI__Mastermind 34840 points

    Hi HXC,

    When increasing the load current, will the audible noise have improvement?

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Prodigy 20 points

    Hi Patrick,

    without load (removing R118 and R117) noise is significantly reduced, almost inaudible. Current absorption is about 20mA +-10% on both channels 

    Below you can found waveform of the output with and without resistors 

    Regards,

    Salvatore

    VNEG - VPOS

    VNEG NO LOAD - VPOS NO LOAD

  • 0 in reply to HXC
    TI__Mastermind 34840 points

    Hi HXC,

    What is the power inductance you used?

    And if you remove the C70/R133, will the noise be reduced?

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Prodigy 20 points

    Hi Patrick,

    The Power inductance is:

    L9,L10 - Ferrite Head 400 mA 25 % IMP=1 kOhms Shielded SMD/SMT DCR=300 mOhms - Pulse Electronics - BBGK00201209102Y00

    Removing C70/R133 (FBP compensation), or C66/R132 (FBN compensation), it makes no change with the noise.

    Do you have any idea what else it could be? Can I do more tests?

    Regards,

    Salvatore 

  • 0 in reply to HXC
    TI__Mastermind 34840 points

    Hi Salvatore,

    What are the inductance of L3 and L4?

    Because you mentioned "If I put my finger on C70/R133 the noise fades a lot becoming almost imperceptible.", so I thought it might be related to this RC.

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Prodigy 20 points

    Hi Patrick,

    inductance L3 and L3 are 

    EPCOS / TDK B82462G4472M

    If it can be useful, the BOM with all the other components are in the first post.

    I agree with you that the problem is related to the RC I identified, but I don't understand how. Could you provide me with more support to resolve the issue? I can run any tests you request immediately.

    Thank you.

    Regards,

    Salvatore

  • 0 in reply to HXC
    TI__Mastermind 34840 points

    Hi Salvatore,

    I will give you feedback later.

  • 0 in reply to HXC
    TI__Mastermind 34840 points

    Hi Salvatore,

    Are you able to capture the load current waveform? Since removing the load can reduce the audible noise so I suspect the voltage ripple maybe caused by the inrush current.

    It will be helpful if you can also capture the inductor current waveform to see whether it has low frequency oscillation.

    BR

    Patrick