• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 64 subscribers
  • Views 562 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.

Trip resistor for Dual channel Buck TPS5120 Multiphase controller

Jun Tan
Prodigy 10 points
Other Parts Discussed in Thread: TPS5120

Hi, I'm currently designing my SMPS to output 8V@1.5A and 5V@1A. Using TPS5120, How do I work out what is the trip resistor value for my design? I can't find any application note to calculate the trip resistor.

My FLT pin measured 2.2V when FETs are forced off by the controller. So, I came to the conclusion that either 3 of the conditions are met. According to my knowledge (from the datasheet) pin FLT will latch the switches if 3 of these condition occured.

1. Over voltage
2. Under voltage
3. Over current
 
Because, my controller keeps shutting off output1 FETs, using a pot I have to set it to somewhere around 45Kohms to avoid tripping. My 2nd channel works fine with 15Kohms.  I contacted TI, and they sent me the loop compensation calculator instead. I was wondering if anyone here can help me on this?

 Thank you very much!

  • 0
    TI__Genius 12740 points

    Team-

    We have another customer with the exact same question- the data sheet does not specify how to arrive at the trip resistors (R8 and R9 of the Figure 1 of the data sheet) connected between VCC and TRIPx terminals.  It appears that this thread has been open for a long time now- can you please suggest an answer ASAP? 

    Thanks and best regards,

    Steven Dunbar, AFA Colorado

  • 0 in reply to Antenna_Head
    TI__Guru 56925 points

    Process for setting trip resistor value:

     

    1) Select Desired Minimum OCP trip point - Rule of Thumb is 130% of maximum load current.

    2) Calculate worst case MOSFET voltage drop at desired OCP trip point - Don't forget to account for thermal effects on Rdson

      V = Iocp * Rdson(max)

    2) Substract worst case Offset (Vos max) to account for measurement error (Not Specified, but I recommend using +6mV)

    Vtrip(min) = Iocp * Rdson(max) + Vos(max)

    3) Divide trip voltage by minimum trip current to obtain resistor value that will provide AT LEAST Vtrip(min)

    Rtrip(min) = [ Iocp(min) * Rdson(max) + Vos(max) ]  / Itrip(min) or Rtrip(min) = [ Iocp(min) * Rdson(max) + 6mV ]  / 11.5uA

     

    Which Rdson do you use?

    Since the controller uses both High-side and Low-side MOSFETs, use the higher Rdson of the two (typically the High-side Rdson)