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UCC29002: Connecting positive to negative buck-boost converter in parallel with UCC29002

Danilo A.
Mastermind 27440 points
Part Number: UCC29002
Other Parts Discussed in Thread: TPS40075, LM27403, , LM2673

Hi Team,

Our customer is looking for a DC/DC converter with Vin = 15V and Vout = - 12V, Iout = 2A and can be connected in parallel to the same DC/DC converter.

He will configure the TPS40075, LM27403 and LM27403 as negative output converter by connecting the output to Ground and use the device's GND as negative output as shown in the application note below

www.ti.com/.../snva022e.pdf

He will use UCC29002 load share controller for this application. Is the UCC29002 suitable for paralleling DC/DC converter with remote sense such as TPS40075, LM27403 and LM27403?

Regards,

Danilo

  • +1
    TI__Mastermind 35290 points

    Hello Danilo, 

    Thank you for your interest in the UCC29002 load-share controller. 

    I think that in principle, there can be a way to configure the UCC29002 to work with a negative output, HOWEVER I am not aware of any prior design examples, so I am not sure how it would be done.  I will have to think about it.  My main concern is that in typical usage, the UCC29002 ADJ current is GND-referenced and applied to a positive-referenced feedback signal.  Conceptually, such a signal could be translated to a negative feedback but I am not sure about performance when the "GND" of the IC is connected to a variable negative voltage, specifically the very same negative voltage that is being adjusted by the ADJ current.  I do not know if this effectively results in positive feedback or not. 

    That said, I think that your customer's plan to use the TPS40075 and/or LM27403 devices in the manner suggested by the SNVA022E Application Report will NOT work because those two controllers rely on the output GND being the same as the input GND and the output must positive with respect to GND.  From my readings of their datasheets, these devices do not appear to have any provisions to accommodate a negative output voltage.  

    So before adapting the UCC29002 for use with one of these controllers, I think your customer should re-evaluate the original plan, and find PWM controllers that are specifically designed for positive to negative conversion with adjustable feedback, such as the LM2673 referenced in the App-Report. 

    Regards,
    Ulrich