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TPS62175: Fails at Input voltages above 16V

Part Number: TPS62175
Other Parts Discussed in Thread: LMR36006

We are using TPS62175DQCR chip in our products to get 3.3V. In one of our product (in development stage ) the input voltage can go up to 21 V. When the input voltage is around 18V the chip fails with the symptom that pin 1 ( PGND ) is shorted to pin 2 ( VIN ). Is there something we’re missing ?

  • Hi John,

    Can you post or send me your schematic, PCB layout, and a waveform of Vin and Vout as the input voltage is increased?

    How are you increasing the input voltage?  Are you just turning the knob on a standard lab power supply?

  • Hi Chris,

    Thanks for your reply.

    I will send the you the schematics and layout privately - the designs are confidential.


  • Thanks for your reply John.  Were you able to start a 'conversation' with me?

    Did you have a chance to measure the waveform?

  • Hi John,

    Thanks for sending your PCB layout.  The input cap is not placed properly and this is the most important component for a buck.  Its GND has a long path, through vias, back to the PGND pin of the IC.

    Can you try manually placing Cin right next to the IC's VIN and PGND pins?  It looks like you should be able to use the existing VIN pad for C10 and scrape away the soldermask to make the GND connection just above the IC.

    We also recommend adding a few GND vias under the IC.

  • Hi Chris,

    We implemented the suggestion of reworking the boards to make sure that the Cin was near the chip and that the chip's PGND was close to Cin GND. 

    However, before implementing the above rework we decided to replaced the damaged IC's ( which were bought in China - our prototype boards were assembled in China with all the electronic components being sourced there ) with new IC's we bought on Digikey. With the new IC's we could increase the input voltage past 18V without damaging the chips. This is contrary to the original scenario - where the original boards ( with ICs from China ) would have the buck IC fail when the input voltage was somewhere around 18V. Any ideas on what this observation could mean ?

    Back to the reworked boards - we modified the boards such that we had input caps increased in value and placed close to the IC. With this modifications we realized that the ICs failed when we hot plugged the boards to power. The input voltage was limited to up to 19V. When hot plugging both the original ICs (from China) and ones bought on Digikey failed even with the modification to increase Cin value and have Cin GND very close to PGND of IC. I have attached some waveforms of how the input voltage shoots on hot plugging power. 

    Is there something that we're still missing ?

    HotPlug - 12.5V 22uF+100nF Ground_Rework No_Bead.PNG

    HotPlug - 12.5V 22uF+100nF Ground_Rework With_Bead.PNG

    HotPlug - 16V 22uF+100nF Ground_Rework With_Bead.PNG

    HotPlug - 19V 22uF+100nF Ground_Rework With_Bead.PNG




    John Ayuya.

  • Hi John,

    Thanks for sending the waveforms.  On the hot plug cases, does only the 19V one fail or do you see failures with lower voltages?  In any case, the overshoot on that one looks like it is right at the rating of the IC.  This could easily cause a failure if it rings above the abs max rating.  Here is a blog I wrote a while ago on this topic:

    It would also be a good idea to look at Vin when the input power is hot unplugged.

    On the steady state increase of Vin case (your initial question), can you post a waveform of Vin during the Vin change?  Does this look different with either set of ICs?  If you want to verify the authenticity of the units you received, these pages have this information:

  • Hi John,

    Are you still debugging this?

  • Hi Chris,

    Thanks for the follow up. I am done debugging - thanks to your information that was helpful and to the point. I did prove that on my test set up the cable from the PSU was causing the ringing - the shorter the cable I used the less the ringing I saw. And our final product will have less than 5 mm of cable / connector to the source voltage; so I think there will be no serious problem related to ringing.

    However, am considering using a regulator with a higher input voltage. In our application the maximum input voltage we expect is 21V and the IC is rated at 28V - do you think this IC gives enough margin ( "derating marging" ) ?

    Thank you,

    John Ayuya.

  • Perfect!  Setup differences between bench testing and the final application can cause issues for sure.  You can also simulate the overshoot with spice and a model of your cable, input caps, etc.

    The derating requirement depends on how much ringing you expect to see in your application and what derating policies your company has.  21V is 75% of 28V.  

    The LMR36006 is a popular higher voltage device and I'm sure there are others too, if you want to go that route.

  • Thanks for your reply.

    We currently use IBM's derating guideline. Even though the IBM's guideline does a good job at derating of most semiconductors such as FETs, diodes, BJTs, Rectifiers, etc. it does not have an explicit guideline on regulators ( I can understand it would a herculean task to list all devices ). So, a look at the table below shows that the most likely place to place regulator is under "Other Types" which they recommend a voltage derating of 50%.

    What would your recommendation be with regard to voltage derating ?

    John Ayuya

  • Hi John,

    We don't have derating guidelines; this is your company's job to tell you what is required for your safety margins in your market and at your customers, etc.

    I will note that such derating guidelines should probably be measured against the IC's 30V absolute maximum rating, rather than the 28V recommended maximum.  Above 30V is what could break the device.

  • Hi Chris,

    Thanks for that information and your help.

    I am glad and greatly appreciate that you made me understand the issue I was facing. I marked the issue as resolved, yesterday.

    Thank you,

    John Ayuya.