• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 232 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.

TPS2350 / SWITCHING BETWEEN POWER SUPPLIES

Ran Feldman
Intellectual 780 points
Other Parts Discussed in Thread: TPS2350

Hi,

Our customer is using the TPS2350 and encountered some problems:

 

Attached are the schematics (load(25W) is located on other pages) based on SLUA468 application report.

3858.TPS2350_HOT_SWAP.PDF1682.TPS2350_HOT_SWAP.PDF

The Customer has 2 power supplies, A (Primary) and B (Secondary) and they want them both to be redundant.  Here is the description of the phenomenon:

 

  • Both A and B power supplies are ON. Channel A is      supplying current (Va>Vb). Decreasing A’s voltage (or increasing B’s      voltage) and when the difference between them is about 0.5V(Vb-Va=0.5V)      channel B takes over and supplies current. All works fine.

 

  • Both A and B power supplies are ON. Channel B      Voltage is higher than A’s (Vb>Va), Decreasing voltage B(or increase      voltage A), A doest take control, nothing happens if even Va significantly      exceeds Vb.the customer checked pins 14 and 13 of the chip (VINA and      VINB) and found that although Ch A voltage decreased, VINA follow to VINB(with      difference 300mV), this is not enough for the comparator to switch to      channel A. This deadlock is permanent: channel A cannot take control over      load. If the customer switched off channel B, channel A does take      control, but only after 1-2 Sec during which the voltage on load dropped      down to zero. This is unacceptable for the design.

 

The customer  tried a separated power supplies, or short connecting RTN_A_F and RTN_B_F signals. Nothing changed.

In summary, the customer wants both supplies to switch between them on one of them encounters a problem.

Please advice,

Thanks

  • 0
    TI__Intellectual 1005 points

    Ran,

    I understand your concern.

    The TPS2350 will switch from supply A to supply B once the difference is bigger than 400mV. Based on your description, |VINA-VINB| ~0.3 so the part is acting properly and doesn't switch. The real question is why the difference between VINA and VINB is only 300mV and we need to investigate this further. 

    Please do the following:

    1) Short RTNA and RTNB

    2) Perform the test you mentioned above and probe VINA-VINB. Since this is the low side you'll start with VINA > VINB and go to VINA < VINB. This corresponds to VA (RTNA-(-48VA_F) increasing.  Observe GATA and GATB.

    3) In your diagram the -48VA_F is tied directly to VINA and the postivite terminals of both the supplies are tied together so I don't understand how VINA and VINB don't track VA and VB... Something has to be wrong with the circuit...

    Good Luck,

    Artem Rogachev

    Systems Enginner / Power Interface