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UCC2818A: They need the variation data of SS terminal charge current (source current).

Kazuya Nakai59
Guru 20660 points
Part Number: UCC2818A
Other Parts Discussed in Thread: UCC2818

Tool/software:

Hello guys,

One of my customers is evaluating UCC2818A for their new products.

At this moment, they have the following questions.
Could you please give me your reply?

Q1.
The device datasheet shows on page 7 that SS charge current is -6uA(Min), -10uA(Typ) and -16uA(Max).
Do you have any information or data about the SS current variation?
The customer want to get any data like a distribution graph of SS current variation.
Do you have such data?

Q2.
They think that SS pin voltage is charged up to about 7.5V eventually.
However they found a device which can not charge SS pin up to 7.5V.
The device SS pin voltage rising is stopped around 1V.
Do you think what the possibility of the cause is?

Your reply would be much appreciated.

Best regards,
Kazuya.  

  • 0
    TI__Mastermind 31250 points

    Hello Kazuya-san, 

    Thank you for your interest in the UCC2818A PFC controller. 

    For Q1:  I am not able to find any characterization data for the UCC2818A device, however, I did find some data for the UCC2818 (non-A).
    I can't share the file, but I can summarize the test results for SS-pin current variation. 
    This file:  8726.Differences between UCC2817A-18A-19A and UCC2817-18-19 slua294.pdf describes that the difference between -A and non-A devices involves only the gate-drive design.
    The rest of the two devices are identical, so SS characterization data for UCC2818 applies to UCC2818A as well. 

    The characterization data of one lot shows that SS charging current averages about 11.7uA with a standard deviation of about 0.3uA.  These data hold nearly flat over the temperature range of -40C to +85C.   Based on this data, it is my opinion that the datasheet min/max limits of -6uA to -16uA are overly conservative.  For example, applying 6-sigma deviation to the mean (Cpk = 2) results in -11.7uA +/- 1.8uA, or min/max = -10uA to -13.5uA.  

    Your customer can expect a similar tight deviation of current from the mean in any given lot, however it is unclear how the mean may vary from lot to lot. 
    I suggest (but cannot guarantee) that a +/-1uA variation of the mean is not unreasonable to estimate, based on other history with TI process control. 

    For Q2:  The block diagram shows no other internal influence on the SS voltage except the connections to the Error Amp, to the current source, and to the external pin. 
    In my opinion, the SS voltage may be limited to 1V due to two possibilities:
    a) external limiting by some unknown, unexpected clamping action by the test equipment (either by test-circuit fault or other undetermined reason), or
    b) internal limiting due to failure of some internal circuit from externally-applied overstress (such as ESD, for example, which exceeded the ESD ratings of the device).

    Regards,
    Ulrich