• State
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 31 views
  • Users 0 members are here
Support feedback
Options
Options
Related

TPS546D24A: VOUT Collapses When VOSNS Connected

Yake Li
Prodigy 120 points
Part Number: TPS546D24A

Tool/software:

I'm using the TPS546D24ARVFR for an FPGA core voltage (0.85V) and hitting a weird issue:

  • When I connect VOSNS normally:
    • EN/UVLO = 1.07V
    • VDD = 4.7V 
    • VOUT = -0.05V

  • But if I disconnect VOSNS (removed R254):
    • Same EN/VDD voltages
    • VOUT =  0.85V

My setup:

  • Layout confession: Sweat smile
    • VOSNS/GOSNS aren’t routed as diff pair
    • VOSNS jumps through a via to another layer

  • Schematic attached for reference

My questions:

  1. Why would connecting VOSNS kill my output?

  2. Can I just leave VOSNS disconnected? 

  3. What should I try next?8304.TPS546D24ARVFR.pdf

  • 0
    Prodigy 120 points

    Hi, 

    After further testing,  POWER good = 0 in both cases.

    I'm still stuck and would really appreciate some help on this. Thanks!

  • 0 in reply to Yake Li
    TI__Guru 56795 points

      

    You have VOSNS connected to the output with no capacitance between the primary inductor L34 and the Ferrite Bead (FB24) so the ripple at the remote sense point will be extremely high, and the ferrite bead will need to carry all of the inductor ripple current.

    Due to the high ripple voltage at the sense point, the output is likely 0V because it's generating OV and/or UV faults and shutting down.

    The schematic also shows a connection between INPUT_GND and ANALOG_GND, but no connection between GND and either INPUT_GND or ANALOG_GND.  The TPS546D24A requires a mounting surface layer direct metal connection between the AGND pin and the exposed pad, the width of the pin-pad (0.2mm / 8mils) 

    With R254 removed, there is no connection from the output voltage to the regulation loop, so I'm not actually sure how it's regulating to 0.85V when this resistor is removed.