WEBENCH® Tools/TPS43060: Rsense value

Roy Chou1

Part Number: TPS43060

Tool/software: WEBENCH® Design Tools

Hi Team,

I use WEBENCH to do the simulation, but Rsense confused me.

My condition is input 5V -> outpu 7V/0.15A in 30C and the Rsense showing in WEBENCH is 330m//330m=165mohm but I use datasheet formula(10) to get Rsense is 375mohm.

I think these two value is so different. how could I choose?WBDesign62 (1).pdf

over 5 years ago

0 Helen chen over 5 years ago

TI__Mastermind 40080 points

Dear Sir,

The Webench result is OK. Please check the Vcs value in the below table, it is 50mV and generally should leave some margin. So I'm curious how did you get 375m ohm?

0 Roy Chou1 over 5 years ago in reply to Helen chen

TI__Genius 16170 points

Hi Helen,

My calculation is

Rsense = Vcs(max)/(Iave_max+delta_IL/2) = 370

Vcs(max) = 72mV (D=0.3)

Iave_max = 0.15A

delta_IL = 88.758mA

Regards,

Roy

0 Helen chen over 5 years ago in reply to Roy Chou1

TI__Mastermind 40080 points

Hi Roy,

You should calculate in below way:

Vcs(min) = 50mV

Iave_max = Vo*Io/0.88

In case there's some noise, Vcs(min) should leave some margin, so you can use 40mV or 45mV in your calculate.

0 Roy Chou1 over 5 years ago in reply to Helen chen

TI__Genius 16170 points

Hi Helen,

I follow the below figure and calculation in datasheet. Could you let me know the comments of your calculation?

Regards,

Roy

0 Helen chen over 5 years ago in reply to Roy Chou1

TI__Mastermind 40080 points

Hi Roy,

In the Webench, Vcs choose 50mV, it will not choose according to the duty cycle.

For the current, Iavg=Vo*Io/Vin/eff., it is around 0.247A, the peak inductor current is IL=Iavg*(1+K)=0.247*(1+0.2)=0.2964A

0 Roy Chou1 over 5 years ago in reply to Helen chen

TI__Genius 16170 points

Hi Helen,

Webench formula confused me..... So don't we follow the datasheet to select Vcs(max)? And when will webench choose D=0 or D=max

As I know, we could set the current limit value by Rsense. For our condition, Iout(max)=0.15A and I would like to set the current limit value = 0.25A

How could I design the Rsense value?

Regards,

Roy

0 Helen chen over 5 years ago in reply to Roy Chou1

TI__Mastermind 40080 points

Roy,

Webench generally should leave enough margin for the customer, so it just use the minimum value. Because we need to consider the noise in the circuit.

For the 0.25A current, it is load current , right? If it is, you need to calculate the related input current.

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WEBENCH® Tools/TPS43060: Rsense value