• State
  • Locked Locked
  • Replies 7 replies
  • Subscribers 63 subscribers
  • Views 952 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS62140 Issues

Yang Wang5
Prodigy 160 points
Other Parts Discussed in Thread: TPS62140EVM-505

Our team is using two TPS62140s as main power regulators on our board to step down the voltage from a higher voltage to 3.3 and 5V. We followed TPS62140EVM-505's PCB layout and the same parts for our boards (just changing some resistor values according to the datasheet to get the desired output voltage). The only major difference is that we have a switch that en/disable the EN pin. We've experienced some issues.

Issue 1: we used both batteries and external power adapter as inputs. For batteries, @6.4V, never had issues; regulators output 3.3V and 5V consistently. However, when we used external power adapters (tried t two, one rated @12V, 6A and the other @6V, 1A), the regulator stopped working completely after power was applied. It was later on found the moment the power is applied, there was sometimes a negative spike from the power adapters. We thought this might be an problem (since abs. maximum rating of the IC's input voltage is -0.3V to 20V) so we put a relatively large cap (3000uF, 25V) on the input pins to avoid this from happening.

Issue 2: With the cap installed on the input, after using our switch to apply power a few times (worked fine), the regulator seems broke. Even with our switch open (EN pin should be low), after applying power, the IC still outputs 3.3V and 5V; it seems like the EN pin is stuck to HIGH. Please let me know if you guys have some insights on these issues.

Thanks!

  • 0
    TI__Guru**** 150870 points
    Could you post your layout for me to double-check?

    What circuitry is between the adaptor and the IC? Do you have a schematic that shows this connection?
  • 0 in reply to Chris Glaser
    Prodigy 160 points

    Chris,

    Before using the big cap (3300uF, 25V) on the input of the IC, there is no circuitry in between adapter and IC; the adapter is feeding directly its regulated DC power t o the IC.

    I will post portion of the schematic and layout if you still need it.

  • 0 in reply to Yang Wang5
    TI__Guru**** 150870 points
    Yes, this is likely not recommended. An adaptor will generate a hot plug event on Vin which causes ringing through the adaptor cable and small on board capacitance. This can easily ring too high and damage the device. This is one reason why we have a relatively small tantalum cap on the input of the EVM--to damp any ringing.

    The same thing can happen with your switch. I would suggest looking at Vin of the device with a scope to observe the ringing.
  • 0 in reply to Chris Glaser
    Prodigy 160 points
    Thanks for advice.

    Maybe I wasn't too clear in the previous posts. Several points:

    1) When doing the layout, we followed exactly the layout that was on the EVM; our board has the small tantalum cap on the input (60uF). But that doesn't help us much from the ringing so we added another 3300uF, 25V cap on the input.

    2) We already see the ringing from the scope before posting the original post. That's why we added the big cap to begin with.

    3) The switch is for toggling the EN pin of the IC. The adapter power is always there on the input; the switch toggles EN to turn on/off power.

    The problem is, after a few tries to turn on/off with the big cap on the input (working fine, no ringing as observed on the scope), the IC stopped working (seems damaged). I even cut the switch connection so the EN should always be low but IC still outputs regulated voltage.

    Any insights on what caused this?
  • 0 in reply to Yang Wang5
    TI__Guru**** 150870 points
    Ah, the switch is on EN. You will likely need debouncing circuitry there as well to prevent voltage ringing/excursions on the EN pin.

    I don't understand how the IC is damaged (it stops working) yet still outputs a regulated voltage. Perhaps posting your schematic would help.
  • 0 in reply to Chris Glaser
    Prodigy 160 points

    Hi Chris,

    Attached are the schematic and board for the regulator portion of our application. The switch is connected to pin 13 of the IC as you could see.

    I pretty much followed the EVM layout and schematic. Any recommendations?

    Thanks.

  • 0 in reply to Yang Wang5
    TI__Guru**** 150870 points
    Thanks for posting. The layout is difficult to read since the planes are not showing as poured, but the concept looks like a copy of the EVM.

    It's not clear what the exact issue you see when you use the EN switch, but voltage excursions could be happening there as well due to the switch. You might try adding some debounce circuitry and see if it helps.