• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 452 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.

TPS62933: Design a variable output DCDC

Steven Wang
Prodigy 230 points
Part Number: TPS62933

Hi, I would like to have the following design

Input side: fixed 24VDC

Output side: use a variable resistor as the feedback high side resistor, generate variable output 1V - 17V, and 3A.

According to the Webench simulation, the TPS62933 works. However, it requires different component values. The main different is the inductor value. 

1. Could l use the middle or largest inductor value to generate 1-17V Vout range? 

2. Could I use the largest capacitor C_in and C_out? 

Thank you

  • 0
    TI__Genius 16632 points

    Hi Steven,

    Thanks for reaching to us.

    Before checking the feasibility of 1Vout~17Vout using same BOM, I want to check your output current (Iout) condition. Is 3A just peak current, average current is lower than 3A? What's your typical average Iout? For 24Vin-17Vout-3A operation, device thermal performance could be a concern. 

    Besides, do you have requirement on switching frequency? 

  • 0 in reply to Miranda Gu
    Prodigy 230 points

    Hi Miranda, 

    I would like to design a general DCDC buck DC power supply which has as wide Vout range as possible, and same Iout range for all Vout range.

    There is no requirements on switching frequency.

    I would like to have I_ripple as small as possible at all ranges, such as 20-30%. 

    So the design is really up to the performance of TPS62933. The final result could be 1-15V, max 2A (any other combinations) depends on TPS62933 capability. 

  • 0 in reply to Steven Wang
    TI__Genius 16632 points

    Hello Steven,

    Got it, the thermal at 17Vout-2A shouldn't be a concern.

    But why you has strict IL ripple requirement? If so, you need to use a quite large inductance, the loop stability at low Vout needs to be considered carefully. Below is our recommended LC table, generally larger Vout will have larger recommended inductance. 

    If you want lower Vout ripple, another good way is to increase output capacitance, which is an effective way to decrease output ripple.

    To be honest, it's hard to find a golden BOM suitable for all Vout conditions, otherwise we will not list the recommended LC for different Vout. I do see some cases like TypeC PD, where needs 5Vout/9Vout/15Vout/20Vout using same LC BOM. May I know why you have this requirement of your application?

  • 0 in reply to Miranda Gu
    Prodigy 230 points

    Thank you very much for your help Miranda.

    Design Requirements: I would like to design a 24VDC input, variable Vout circuit. The feedback resistor is a variable resistor which controls Vout. 

    My Proposal (unsure if it works or not): Ideally, I wanna output 1-20V, 3A. However, due to the limitation of buck IC, I would like to investigate the the widest Vout range at 2 or 3A load. Could I choose the middle range design (10V 3A). Then, the product will has the min ripple at 10V 3A, and slight larger ripple at 5V and 15V, 3A? I plan to use a slightly large L and very large C_in, C_out to reduce the output ripple.

    Do you think the proposed idea is feasible? Thanks 

  • 0 in reply to Steven Wang
    TI__Genius 16632 points

    Hello Steven,

    According to IL ripple formula, 50% duty-cycle will have largest IL ripple, so it will be 12Vout, not 10Vout.

    The inductance is related to device loop response. Using same inductance for whole Vout range, need to check loop stability in every condition. It's not that easy, need both simulation and bench tests. Please check again the necessarily.