TPS61088: Review of Passive Component Calculation at COMP pin

saiteja manchukanti

Intellectual 330 points

Part Number: TPS61088

Hello,

Here are the details of my TPS61088 IC's application.

Switching Frequency (Fsw) - 600 kHz
Frhpz - 225.71 kHz
Loop Gain crossover frequency (Fc) - 45.14 kHz
Output derated capacitance - 32.35 uF

As per the formulae in the datasheet, calculated values for R5, C5 and C8 are as follows.

R5 - 53.88 kOhms
C5 - 1.7 nF
C8 - 0.29 pF

And selected values for design are

R5 - 53.6 kOhm
C5 - 10nF
C8 - Left open as the calculated value is less than 10 pF

Please suggest whether we can go ahead with the selected values in the design?

Here is the link of the datasheet for your reference - http://www.ti.com/lit/ds/symlink/tps61088.pdf

Regards.

over 6 years ago

0 Helen chen over 6 years ago

TI__Mastermind 40080 points

Dear Sir,

Why you choose 45.14kHz cross over frequency? it is very high for the boost converter

0 Helen chen over 6 years ago in reply to Helen chen

TI__Mastermind 40080 points

For the boost converter, generally we set the fc at less than 20kHz. 10kHz is a common choice.

0 saiteja manchukanti over 6 years ago in reply to Helen chen

Intellectual 330 points

Dear Helen Chen,

Thanks for your response. As mentioned in the datasheet, loop gain crossover frequency should be no higher than 1/10th of Fsw and 1/5 of Frhpz. I have chosen 1/5th of Frhpz as loop gain crossover frequency.

However, I will change the loop gain crossover frequency to 10kHz and recalculate the values of passive components for loop compensation.

Please tell whether I am heading towards correct direction?

Regards.

0 Helen chen over 6 years ago in reply to saiteja manchukanti

TI__Mastermind 40080 points

Yes， u're heading toward a right direction.

What is your Vin, Vo, Io? So that I can have a double check!

0 saiteja manchukanti over 6 years ago in reply to Helen chen

Intellectual 330 points

Hi Helen,

Here are the details of the applications

Application 1

Vin - 3V to 4.2V

Vout - 8.4V

Iout - 1.485 A. (This current is drawn periodically once in every 10 seconds)

Application 2

Vin - 3V to 4.2V

Vout - 6.6 V

Iout - 1.89 A. (This current is drawn periodically once in every 10 seconds)

Please tell how you are checking, so that I can do the same for our other applications.

Regards.

0 Helen chen over 6 years ago in reply to saiteja manchukanti

TI__Mastermind 40080 points

Dear Sir,

It depend on your effecting Cout, which is the Cout after derating. And you can get the Rc, Cc, Cp by the following equation.

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TPS61088: Review of Passive Component Calculation at COMP pin