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TPS7A47: TPS7A47 - Parallel Operation via TIDA-01232

Part Number: TPS7A47
Other Parts Discussed in Thread: , TPS7A85

Hello all - 

I require a high current and low noise (High PSRR + low output noise) 7.5V supply that is capable up to about 2A. We also require good transient response ~100mV pk-pk change settling within 3-5us with a 10mA-2A pulse. The 2A-10mA transition can yield more of a spike. 

Normally, you'd use high ballast resistors or try to use opamps in the feedback network; however ballasting is inefficient and the opamp solution seems complex. 

This appnote describes a very similar part being used in parallel by joining the NR pins. It seems that by doing this, you're pretty much guaranteed to be within 0.1% from part to part; which makes ballasting very easy. In the appnote, they've used 5mOhm PCB traces for this. 

My question is, can the TPS7A47 be used in the same manner? 

I would normally just buy a couple evaluation kits and try it; but it seems that these aren't available. I'm skeptical of using simulation, as I don't believe it accounts for device-device variations - and it may give me a false positive.

Can anyone comment on this? 

thank you - 

Stephen

  • I forgot to explicitly link the reference design in question:

    https://www.ti.com/tool/TIDA-01232

    https://www.ti.com/lit/gpn/tps7a47

    Thanks! 

  • Hi Stephen,

    Yes you should be able to parallel this device using the NR pin, much like the app note you linked to.  The TPS7A47 EVM (part number TPS7A4701EVM-094) is in stock but you are correct that the reference design is not orderable.

    Thanks,

    - Stephen

  • Awesome, thank you fellow Stephen ;) 

    I did look at the internal diagrams, but it didn't seem obvious that they worked exactly the same like this. Do you know that this has been done before, successfully? Or, are you more familiar with the internal details of these parts than what published information could provide?

    I may order a couple of these kits and try it before I commit it to my larger hardware project. 

    thanks again! 

    Stephen

  • Hey Stephen,

    I don't have readily available test data for paralleling the TPS7A47, but it should still work the same way.  It looks like another customer asked about paralleling the TPS7A47 some years back on an internal E2E forum post, and the engineers back then said it would work as well.  So it is likely being done by other customers, although I don't have the test data. The TPS7A47 is a very popular device and I would be surprised if multiple customers were not doing this, and we just weren't hearing about it.

    The TPS7A47 has an NR pin that you tie together just like the reference design.  The TPS7A47 and the TPS7A85 both have a large internal resistor that acts as part of the RC filter with the NR capacitor.  They both have a "fast charge" current source to turn on the device in a reasonable amount of time.  The concepts look the same to me.

    Thanks,

    - Stephen

  • This is great news - thank you very much for the further information. What I was really looking for was a bit more certainty, as I will likely end up rolling it into my larger design without going through the hassle of fully validating it on the evaluation boards. 

    I really appreciate it. It would be really neat if TI added this to their appnote, as I had to dig a bit to find a solution that utilized this really fantastic part.

    Stephen

  • Sounds good Stephen, let us know if we can help any further.

    Thanks,

    - Stephen