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TPS40170: 5V,7A Power supply issues

Part Number: TPS40170
Other Parts Discussed in Thread: TPL5010,

Hello,

I designed a circuit with ti webench, I have some issues in the revision A. I discussed the issue on forum on the below link.

e2e.ti.com/.../2220524

Now I redesigned it. I added 10R resistors at MOSFET gate and layout changed to 4 layer as per the datasheet and webench.
Now my powersupply is turning on when i place the board on an ESD protectionn sheet once it on then the ESD protection sheet can remove. Without the ESD protection sheet the power supply is not stable there is a dip in the output as shown below.

its output wave is shown below.

Now I changed the gate resistor to 15R, then the power supply is turning on normally without an ESD protection sheet.

Kindly help me to solve this issue.

Regards

Sebastian

  • Can you post your schematic and layout? Can you provide a waveform showing the switching node?
  • I hope you understood our issue. Actually, I have one more point to mention. We are using a watch dog timer circuit using TPL5010, in order to wake up the raspberry pi, which is the core unit, in case of software hang. Please find the attached circuit of power section and watch dog timer section below

    When the board is powered after placing on ESD sheet, there is no issues and everything works fine. But when it is powered without ESD sheet, its power supply indication LED is blinking indicating power dip, so the raspberry pi won't boots. At this time, when we touch the power supply IC, TPS40170, with and ESD cover, suddenly Pi boots. Another observation is, when we by-pass the WDT functionality by R21 resistor, everything works fine with or without ESD sheet.

    After lot of thinking and observations, we have changed the gate resistors, R3 & R15 to 15 Ohms instead of 10 Ohms to slow down the switching speed. Then all the issues were disappeared and never observed even a single time in multiple power cycle test. But we still didn't get the exact reason of why it is happening like this and what is the significance of ESD sheet. We have to find the exact reason because it shouldn't happen in customer site. We really need your help for this :-)

    Please find the screen shots of gate signals and output below

    Please find the layout files also in the order of layout top, layout bottom, layout power and layout ground.

    Also attaching top layout PDF fileAQUADAACS_CAR_TOP_REVB_11AUG2017.pdf

  • Hello,
    Kindly help me on the above issue. Waiting......
    Regards,
    Sebastian
  • I will assign this to someone who supports TPS40170.
  • Sebastian ,

    Can you please provide input and inductor current  waveform when the output goes low ?

    Further here are few comments on your layout and Schematic :

    1. I dont see any decoupling cap on Vin pin of the device . Please place a cap as close as possible to the pin and GND .

    2. I see only one Ceramic Cap C7 at the output . Is it 6.3V rated X7R cap ? The DC biased Ceramic cap loose their capacitance at higher voltage . You may want to add Ceramic + Electrolytic combo or atleast few ceramic caps in parallel . The design ca be recompensated using the attached excel calculator .

    TPS40170Type III Loop Stability 5V_7A.xls

    3. Since you are not using Master /Slave functionality , you may want to remove M/S pin connection to VIN and left it floating . May be there is coupling of noise on SYNC output (which is left floating) creating issue in the design .

    ----Ambreesh