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TPS746-Q1: Using two voltage regulators in parallel to increase the current output

Nikhil Sharma
Prodigy 15 points
Part Number: TPS746-Q1
Other Parts Discussed in Thread: TPS7A52-Q1, OPA388

Tool/software:

Can I connect the output of two TPS746-Q1 in parallel to increase the current output? 

I have a circuit where I would be needing 3.3V at 1.2-1.6A. Due to size restrictions I am looking at smaller regulators and TPS74633PQWDRVRQ1 is small enough that I can use 2 or even 3 of them.

So, can i just stack them in parallel to share the load amongst them?

  • 0
    TI__Mastermind 36705 points

    Hi Nikhil,

    The short answer is that yes, you can parallel this LDO however you'll need additional components which will make the solution size larger.  Can you use the TPS7A52-Q1 instead?

    Thanks,

    Stephen

  • 0 in reply to Stephen Ziel
    Prodigy 15 points

    Hey Stephen,

    Thanks for your reply !

    TPS7A52-Q1 would be the perfect solution but TPS746-Q1 is cheaper and easier to source than TPS7A52-Q1 for me.

    could you tell me how i can go by using multiple TPS746-Q1 together? 

    thank you very much in advance.

  • +1 in reply to Nikhil Sharma
    TI__Mastermind 36705 points

    Hi Nikhil,

    If you wish to parallel the TPS746-Q1 then you'll need to use one of two techniques. 

    Technique 1: ballast resistors
    The first technique uses ballast resistors on the outputs of each LDO.  The outputs of the ballast resistors are tied together to connect each LDO output together and parallel the LDO's.  The ballast resistor is selected based on the error voltage, which is the maximum difference of the output voltage between each LDO.  A significant percentage of the error voltage comes from the tolerance on the reference voltage itself, so ideally this reference can be tied externally between LDOs to completely eliminate this error.  This would be an NR/SS pin in modern LDO's.  This is the main issue with the TPS746-Q1: You cannot tie the references together so the error voltage may be large, and your ballast resistors may be larger in value than desired.  I have written comprehensive collateral on this topic which you can find below:

    Parallel LDO Calculator

    Parallel LDO Architecture Design Using Ballast Resistors

    Comprehensive Analysis and Universal Equations for Parallel LDO's Using Ballast Resistors

    Technique 2: Op-amp and current sense resistors
    The second technique uses small current sense resistors in series with Vin of each LDO with an op-amp to parallel the LDO's.  The output of the op-amp is tied to one of the LDO's FB pin.  Unfortunately, comprehensive literature on this topic is lacking in the industry (and I have not had a chance to write it yet).  So you are free to pursue this option however we can only offer general guidance on it.  Here is a reference design that shows the concept for another LDO.  I'm using the OPA388 configured as an integrator for another parallel reference design (in work) and other op-amps with lower cost may also work but you'll have to assess those.

    https://www.ti.com/tool/TIDA-00270#design-products

    Thanks,

    Stephen