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TPS62163 minimum output current for correct output voltage

Other Parts Discussed in Thread: TPS62163, TPS5450

I use a TPS62163 (L: 2.2µH, Cout: 2x 10µF) to generate 5V for USB port from a 11.8V rail.

We got resports of some USB stick failing in the field after been used with this power.

I inspected one device ( and got 7.36V on the output instead of 5V, DCDC is switching +/- 3ms.

Adding a USB key (small current) doesn't change the output voltage.

At max current (add 10R power resistor for 500mA USB) the output voltage is 4.93V, switching is 50% 120ns pulses.

So at high load the output voltage is correct, but not at low and the device is switching and not totaly dead.

Any idea what can be the cause of this malfunction please ?

 

  • Since you have used the fixed output voltage version, and now it is giving the wrong Vout (at any load), it seems the device has been damaged.  To confirm this, I would remove a failing device and solder it onto the EVM (a known good board) and see if it still outputs too high a voltage.

    If it does still output 7.xV, then your local TI or distributor FAE can help you debug your design for the cause pf the failure.  2 common locations to check are an overvoltage on the output or input.  So, look at Vin and Vout when input power is applied and removed.  Do this again for when something is plugged in our out of the USB port.  Voltages excursions past the absolute maximum ratings can damage the device.

    There is no minimum load required for output regulation.  See figure 13 in the D/S for an example.

  • Hi Chris,

     The input voltage to the DCDC is produced by a TPS5450 and will not go mutch higher than 12V because we added a transorb (SMAJ12A) on the power line.

      I found another post on the TPS6213x stating that suppling a voltage on the output isn't a problem, the only voltage available to put on the output would be 5V from another  USB, can this damage the device in any way to put 5V on the output at any time ?

    I will check if it will be possible to remove the part and place it on a good working board, but it will be difficult because of the verry small QFN size. 

     We already have more than 100 working boards in the field so I don't suspect the design but bad manipulation.

    regards,

    Steve

  • Yes, there is no issue with a dc voltage being applied to the output but it is how that voltage gets there that may cause issues.  Applying 5V through a cable, for example, might cause ringing and overshoot through the cable which might cause the output terminal to see higher than 5V when the 5V is applied.  Especially if the output goes directly to a USB port that a user can contact, this opens up a lot of failure possibilities since the user can really apply any signal to the output.

  • Of all devices used in our lab (30 pcs) only one was faulty at 7V, so I'm taking a closer look at spickes on the input voltage.

    The supply voltage of 11V is also routed to an external display, and one could disconnect it while the voltage is on. When disconnecting (or connecting) this external load to the supply voltage it rings up to 12V (blue) and more.  These transients are transfert on the output of the regulater (cyan).

    How can I inprove the transient respons on a fixed output regulator ? (slva289 is only for FB devices) or is this not a problem for a USB device ?

    Some trancient on the input are up to 15V (from TPS5450).

     

  • It is most likely that these are not transients at all but rather noise pickup from the act of removing the display.  The timescale is too short (400 nsec) for the IC to do anything.  400 nsec is the typical length of one switching cycle.

    More output capacitance generally increases the regulation of the supply but I think all you're seeing is noise pickup here.

  • I placed the probes very close to the chip (max 3mm) with very good ground connection, output is 2 x 10µF and the load is a small USB stick. 

    Do you mean it's noise on the input or output voltage  or both ?  I could understand noise on the output because of spikes on the input, but the trancients on the 11V input are real ?

    The max supply voltage of this DCDC is 17V, would a spike of 20V or 24V @ 400ns cause any damage ?

    This is the only out of spec that I can measure on the boards (if the measurement is correct ?), spikes on the input voltage when the external display is disconnected (what is normaly not done).

    Maybe I should have a look at the 11V regulator TPS5450 to reduce the output swing when disconnecting the extra load.  There's no cap in the FB of this DCDC.

    Or should I add protection like a transorb to protect the TPS62163 against to high input voltage ?

  • Well, it's likely noise picked up by the probes from the air.  The disconnected circuit creates a fast dV/dt that propagates through the air.

    If the display were consuming any current, then removing it would remove that current from the load on the 11V.  This would be seen as a load step by that converter.  This response could be seen on the scope but would be over some 10 or 100 usec timescale.

    Since you are powered from an upstream switching converter and not an adapter, the input source is not likely to be the cause of the failure.  I still suspect the output side, since the user has access to this, anything can possibly happen.

    It's always good to check your board layout as well, as poor board layout can cause failures of switching power supplies.