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LM5033: SS/SHDN pin

Yury Krivtsov
Prodigy 10 points
Part Number: LM5033

Hello!

I met a strange problem with this IC. It works fine but doesn't shut down when pulling pin 10 (SS) down to ground. Even if I do it just by shortening it with a wire.

It works fine in the other project. The only difference is that it is supplied by 24V at pin Vin. In the problem project Vin and Vss are connected and supplied by 12V. But it seems this is not the reason.

The artwork is straightforward. Everything is close to the IC. Capacitors are present. 4-layer PCB so it's OK with groundplanes etc. I spent a week already, changed several ICs but still at a loss. 

No I am not a novice :)

  • 0
    TI__Mastermind 34465 points
    Hello Yury,
    You did not attach any waveforms so I would like to ask :
    (1) Did you measure a gate drive output when the soft start pin is less than 0.25V ?
    (2) With the output discharged, did you measure a soft start into a full load condition ?
    (3) Have you tried shorting pin 10(SS) directly to pin 7 (GND) and powering up the unit ?

    It is unlikely that the ic is bad because this parameter is tested before the LM5033 is shipped so I think there is either a noise issue holding a residual voltage on SS, a measurement /test issue or a pcb or schematic error.
    Regards
    John
  • 0 in reply to John Griffin1
    TI__Mastermind 34465 points
    Hello Yury,
    I am going to close this post since there has been no new communication in almost 2 weeks.
    Please open a new thread if you need further help.
    Regards
    John