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WEBENCH® Tools/TPS53515: Check the design of my power supply

Jordan MICIAK
Prodigy 10 points
Part Number: TPS53515

Tool/software: WEBENCH® Design Tools

2019-10-08_04-56-571.pdf

Hello everyone,

I tried to calculate all components for my design because I am using a 3.3V for the input (i cannot use higher). The problem is that the simulation software is limited to a minimum of 4,5V input.

My calculation:

Choose the inductor:

L=3IoutMax*fsw*(VinMax-Vout*VOut)/(VinMax)

=  312*500k*3,3-0,8*0,8)/(3,3)

=303 nH ~ 330nH

For the peak I decide to use 30% of the maximum output current à 15,6A

IindPeak=Vtrip8*RDSon+1L*fSW*VinMax-VOut*VoutVinMax

IindPeak=10μ*Rtrip8*RDSon+1L*fSW*VinMax-VOut*VoutVinMax

 

IindPeak= 10μ*56,2k8*5,9m+1330n*500k*3,3-0,8*0,83,3=15,74 A

RTrip = 56,2kOhm

 

Calculation Rfbt / Rfbb for output voltage (Rfbb recommended between 1k and 20 k):

Rfbt=(Vout-0,6)/0,6*R2=(0,8-0,6)/0,6*10.2k= 3.4k kOhm

 

Mode operation : Skip à Rpgood = 150k on Mode pin

Choose switching frequency: Set to 479,17 kHz

(R5 (rf low) and R4(rf high))

R5 = 68,1k and R4 = 249k à frequency 478,18kHz

Vripple ? I am stuck because I am not sure of the IL Ripple, is it 30% of iL max ?

 

How can I calculation or dimenssion my by-pass capacitor ? in the schematic in copy I use the simulation for 5V input and then I modify the differents resistor/inductor and I keep the capacitor.

Please give me an answer soon ! Have a nice day.

Jordan

  • 0
    TI__Mastermind 23955 points

    For the TPS53515 to operate below 4.5V on the VIN pin,  the device must have >4.5V on the VDD pin to operate. 

    You can use the 4.5V input in webench to estimate the component values for the 3.3V input,

    the L and C values are not significantly different. 

    ILripple  is 1/3 of 12A output as you used above.     or      ILripple =     (Vin-Vout)*(Vout/Vin)  *1/(fsw*Lo) using your actual Lo value. 

    For Skip mode , connect MODE to GND with 0 ohm or 150kOhm from Table 4 of TPS53515 datasheet.

    Most developers place resistors on MODE pin to PGOOD and MODE to GND for max flexibility, and nopop the resistor that is not needed. 

    R4 and R5   are 240kOhm    71.5kOhm  from table 1 for 500kHz in datasheet page 16   

    yes     ,  Rfbt=(Vout-0,6)/0,6*R2=(0,8-0,6)/0,6*10.2k= 3.4k kOhm  

    See page 80 -82 of the following datasheet or Input Capacitor and Output Capacitor calculations

    http://www.ti.com/lit/ds/symlink/tps546c23.pdf

    Best Regards,

    David