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Original question:

POWERSTAGE-DESIGNER: Loop Calculator Window

TPS54620

Cookie
Prodigy 145 points
Other Parts Discussed in Thread: TPS54620

Hi 

I want to design " CMC Inverting Buck-Boost"  (Compensation Network is Type2 Transconductance)

There are several questions:

1. Does Vref is fixed in Loop caculator?

2. How do we decide the current gain & Vslope(I mean : Rs ? As?) If I want to design the current gain =0.2 , Rs=200m As=1 --> Is it right?)

Thanks! 

  • 0
    TI__Guru 56825 points

     

    1) Yes, the reference voltage for the TPS54620 is internally fixed at 800mV

    2) The TPS54620 uses internal Rdson current sense.  The Current sense gain is set at 16A/V internally to the device.  The effective Rsense for the current loop is 1/16 = 62.5mOhms.

    3) The TPS54620 has internal slope compensation.  I don't see the details of the ramp in the datasheet.  If you need them, let me know and we will get them for you.

  • 0 in reply to Peter James Miller
    Prodigy 145 points

    Ｈi Peter

    Thanks a lot!

    So how do I set the Ｒs As Vslope in TI's Power Stage DEsigner Tool

  • +1 in reply to Cookie
    TI__Guru 56825 points

     

    I provided you with Rs, which is 62.5mOhms 

    As is the current sense gain, which is already included in the Rs in this case, so you'll want to set it to 1.

    Vslope I will still need to look up, but starting with 0 would provide a conservative guidance for loop design.

  • 0 in reply to Cookie
    TI__Guru 56825 points

     

    The Slope Compensation in the TPS54620 is 9A or per switching cycle or 0.5625V per switching cycle.

    I Believe the Power Stage Designer tool wants the slope compensation in peak voltages not per switching cycle volts, so you need to apply a --VOUT / (VIN - VOUT) duty cycle factor to the slope compensation.

    Since the TPS54620 will see the full VIN - VOUT voltage (VIN + |Vout| ) since Vout is negative) it is important to make sure VIN - VOUT does not exceed the TPS54620's input voltage range.