• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 62 subscribers
  • Views 820 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

TPS4811-Q1: Working with motors ( back EMF problems )

TPS4811-Q1: Reverse current protection with back-to-back or ideal diode?

MarkM
Prodigy 70 points
Part Number: TPS4811-Q1
Other Parts Discussed in Thread: LM74930-Q1

Tool/software:

Hey there,

If I may, a bit of a sanity check that I am not about to do anything outside the scope of the device, and a couple of questions.

I have an application where I need to dynamically connect a charger (up to 90A) to a battery system (48V), and have OV, UV and over current protection.  It also needs to ensure that no voltage is present at the charging port from the batteries in the situation where the TPS is told to turn 'off' (INP low). The charger will not provide power unless it sees a (battery) voltage at the charger port, so I need to power the TPS48110 via diode oring as per the EVM schematic. I think my general scheme for this (shown below) is ok.

1.  I have a concern that if the charger is disconnected under load, there might be a negative going current spike from the battery end due to the inductance in the cables. The cables are short, but naturally I don't want to blow anything up and I presume this spike could destroy the mosfets.  In order to prevent this, I was looking at reverse current protection (battery back out towards charger) but am a bit confused by two options.  

I see on this answer (https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1343268/tps4811-q1-working-with-motors-back-emf-problems/5122464?tisearch=e2e-sitesearch&keymatch=TPS4811%252520lm5050#5122464) you have suggested an LM5050 to prevent such a spike due to back EMF, but was wondering whether the back-to-back mosfet set up shown in the TPS datasheet (page 25) will also do reverse current protection (similar to how the LM74930-Q1 seems to)?

2.  I am unsure what factors are involved in determining the maximum number of mosfets the TPS and LM5050 can drive.  I currently have two (option for a third for thermal considerations) IPT015N10N5ATMA1 mosfets being driven by each of the chips.  I have read that the TPS can drive multiple fets and the LM5050 can drive at least two.  Any guidance on how I determine the maximum drive ability of them would be helpful.

Thanks again!

  • +1
    TI__Mastermind 35575 points

    Mark,

    Thank you for the extremely detailed post. 

    For #1- the best recommendation we give in this case would be to have a TVS diode on the output of the switch to clamp the negative voltages due to the inductive turn-off (and would likely be a good idea if there are these sort of hot plug events anyways.

    When paralleling the FETs, the turn on time will increase as you will need to scale up your charge pump cap as well. Since charge pump cap is bigger, it needs time to reach certain threshold (8.6V).

    Also, you can add ~5-10ohms gate resistor at each FET gate to dampen oscillation due to parasitic. Note we have several great design calculators that help with component/FET selection located at:

    https://www.ti.com/tool/download/SLURB09

    https://www.ti.com/tool/download/FET-INRUSH-SOA-CALC

    Best Regards,
    Tim

  • 0
    Prodigy 70 points

    Hi Tim, 

    Thanks for getting back to me. Great!  I already have bidirectional TVS’s at both ends of the circuit and 10r gate resistors. 

    Also thanks for the info about the charge cap needing to be bigger, I will calculate that and compare it to what I have. 

    And thanks for the fet design tools. I had no idea you supplied them.

    cheers

    Mark

  • 0 in reply to MarkM
    TI__Mastermind 35575 points

    Mark,

    You mentioned it on another thread- but the password to unlock the design calculator is INRUSH. Not quite sure why we locked that design calculator- but in the future we will just have them open. This should help enable you to remove the design limits.

    Best Regards,
    Tim 

  • 0 in reply to Timothy Logan
    Prodigy 70 points

    Thanks for that!  Yes, I moved the question to a new thread then realised I had misunderstood one of the values so deleted it.  Thanks for the password though!