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Original question:

UCC29002: difference between UCC29002, UCC29002-1 and UCC39002

UCC29002: Current Sharing Instability After Startup with UCC29002

Conor
Guru 12115 points
Part Number: UCC29002

Tool/software:

Hi,

We are currently evaluating a parallel power supply configuration using the UCC29002, and we are observing unstable current sharing after startup — the load current is not balanced properly between the modules.

According to the datasheet and application notes, we understand that UCC29002 enters a defined startup mode under the following condition:

  • When V_CSO < 0.8 × V_LS

  • During this mode, the ADJ pin is forced to 3 V to sink the maximum adjust current

  • The LS Bus Driver is disconnected via the Disconnect Switch

We suspect that this behavior is causing the output voltage to rise too rapidly, possibly leading to overcompensation. As a result, the difference between V_CSO and V_LS may oscillate, and the current loop fails to stabilize.

In contrast, when we replaced the UCC29002 with the UCC29002-1 on the same board, the current sharing was much more stable and no such oscillations were observed.

We would appreciate your guidance on the following points:

  1. Have there been any prior reports or known issues regarding instability caused by repeated entry into the startup mode of UCC29002?

  2. Is it possible that fluctuations around the startup mode threshold (V_CSO < 0.8 × V_LS) could prevent proper initiation of current sharing control?

  3. Would TI recommend replacing UCC29002 with UCC29002-1 in cases where stability during startup is critical?

We appreciate your support and look forward to your advice.

Best regards,
Conor

  • 0
    TI__Genius 12795 points

    We will get back to you by next week.

    Thanks

  • 0
    TI__Mastermind 40350 points

    Hello Conor, 

    1. I have heard of cases where current sharing at start-up was unstable and varied widely, but eventually settled out.  I have not heard of sustained oscillations due to this kind of start-up, but that does not mean it has not happened. 

    2.  Yes, it is possible that such fluctuations of Vcso and Vls may cause instability, but it is also possible that the current-loop cross-over frequency has not been set sufficiently lower than the voltage-loop cross-over frequency.

    3.  Yes, I would recommend using UCC29002-1 in place of UCC29002 in cases where stability at startup is critical. 

    Regards,
    Ulrich