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UCC29002: UCC29002DR Current Share Application with Adjustable Voltage 4-18V

Dimitrios Koutsogeorgos
Prodigy 10 points
Part Number: UCC29002

Tool/software:

Hi,

I am using the UCC29002DR IC with the external BJT connected to the ADJ pin.

In my application UCC29002DR is needed for n+1 redundant operation of DC/DC Converters. The output of those converters can be varied between 4-18V.

By having the npn BJT connected in the ADJ pin of the UCC29002DR the IC can anticipate voltages more than 12V(VDD is 12V).

My question arise from the datasheet of the UCC29002DR which states:

The voltage of the VEAO pin is the same as the voltage of the voltage sense amplifier CSO (correct me if I am wrong) which in my case is around 2V. So the voltage of the ADJ pin should be greater than 3V.

So, my question is this: Is there a way to have a minimum 3V at ADJ pin (while having the npn BJT connected) when the converters output are configured at 4V?

My only thoughts to overcome this issue is to somehow bypass the npn BJT when the output voltage of the converters is below a certain limit.

Thank you in advance for your help!

  • 0
    TI__Genius 9550 points

    Hello Dimitrios,

    Is your system similar to the schematic below on page 15 of the datasheet?

    I do not see why you need to worry about a minimum 3V at ADJ pin. The output voltage is not dependent on the voltage at the ADJ pin. The ADJ pin just allows a place for the current in the converter feedback loop to sink. Thus, the converter will detect a lower feedback voltage and try to increase the output voltage in response.

    I think it would be helpful to look at the block diagram to understand how the UCC29002 works. The block diagram on the datasheet is good but we have another diagrams that shows both the internal and external circuitry. 

     6283.UCC29002 Sharing Blocks2.pdf

    Regards,

    Jonathan Wong