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TPS62177 Design Review

Thomas Forster
Prodigy 180 points
Other Parts Discussed in Thread: TPS62177

Hi
with the help of WEBBENCH I have painted an implementation.
For C1, C2 and L1 I used the values recommende by WEBBENCH (2.2uF, 22uF, 10uH).
Input is 17V to 18V and current bewenn 100 mA in standby and around 400mA when the ESP8266 is transmitting

Please find attached a part of the Schema and the board.

I would be most garteful if somone could Review and tell whether this is gonna work or not (before I order some PCBs...).

Tank you and best regards

Thomas

  • 0
    TI__Guru*** 148040 points
    It looks like you did substantial modifications to what Webench gave you? There are many errors. Please read the D/S to check your circuit schematic and layout.

    The inductor needs to connect to SW. VOS connects to the other end of the inductor, the output cap, and the output voltage. NC should be grounded.

    What part numbers are you using? These are critical as well.

    Neither capacitor is placed properly in the layout. The inductor should rotate 180 degrees and connect to a properly placed output cap.

    Can you use thermal vias under the IC?

    Finally, what is the voltage range of the AC source you are rectifying? The TPS62177 is rated up to 28V. Could you have spikes above this?

    Lastly, I suggest adding extra input capacitance per my blog: e2e.ti.com/.../what-is-that-giant-tantalum-cap-on-the-input-of-the-evm It does not appear that your circuit is supplies from a low impedance source as usually done.
  • 0 in reply to Chris Glaser
    Prodigy 180 points

    Holy moly....

    Thank you Chris for preventing me from ordering these PCBs...
    It all started with swapping 2 pins on the Schema. Lousy...

    So here is my second attempt:

    Input: Square wave (PWM) signal with +/-12v to +/-18V
              Other loads on the same signal are PWM Decoders that drive Motors.
              Signal ist generated by amplifiers capable of sourcing 5 to 10A.
              Wires for the source can be several meters long.
              There no big spikes on the line because all loads are behind bridge rectifiers.

    Local load: An ESP8266, I2C Mux, I/O Expander, 2 I2C infrared proximity sensors.
              Normal consumption about 80 to 100mA, while ESP8266 WiFi sending maybe 200 to 300 mA
             The bottom (blue) layer is all GND, so I put some additional termal vias from the top to the bottom..

    C1 ceramic 100nF, C2 ceramic 22 µF, C3 ceramic 47 µF
    L1 as suggested in the design) Bourns SDR0503-100ML
    C1, C2: I thought it might be a good idea to place a small cap as close as possible to the chip an a larger one near to the bridge.
    I don't need PG, so I left it open.

    Now I hope you can give me hope that this design will work at first go .....

    Thank you for your valuable help and
    Best regards
    Thomas

     PS: WEBENCH is a very valuable tool. Without it, I woul have a hard time to find the right chip in the jungle of the switching Regulators...

  • 0 in reply to Thomas Forster
    TI__Guru*** 148040 points
    This looks much better.

    I recommend using a shielded inductor instead.

    As well, it is better to remove the extra copper on the SW node below the inductor. This is just radiating more noise and not helping anything.

    I recommend replacing the 0.1uF C1 with a 2.2uF. And replace C3 with some sort of cap with ESR. This will snub ringing from your long input cable connection.

    Finally, it looks like your load is powered from the trace going from L1 to the right. This is quite narrow. It should be wider.
  • 0 in reply to Chris Glaser
    Prodigy 180 points
    Hi Chris
    I have now implemented your suggestions: Replaced C1 with 2.2µF, C3 with a tantalum 10 µF 35V and the inductance by ASPI-0418FS-100M-T3 from Abracon.
    So now is time to order a small PCB quantity and keep the fingers pressed....
    Thank you for your support and
    Best regards
    Thomas