TPS55332-Q1: Design procedure example and confirmation tool

Christian Yanez

Part Number: TPS55332-Q1
Other Parts Discussed in Thread: LM5158, LM5157

Tool/software:

Hi,I want to use the TPS55332 in a new design and to do so, I'm trying to understand the example implementation in the section 8.2.1 (datasheet) and I can't understand where some values come from, especially in the output capacitor selection (8.2.2.1).
For example, using the equation 19 the output capacitor value is 0.37uF, I replace the design parameters according to table 1 (datasheet) and I can't get the same result.

I use:

Vin = 14V

Vo = 25.5V

fsw = 2MHz

Io(max) = 0.3A

$▲Vo = 0.52$

$Then, C > 0.13 uF$

$On the other hand, in equation 26, what are Itran and Vodrop?$

$Finally, is there a tool that I can use to verify or validate my design in the future?$

$I'm sorry if the question is so silly.$

$Best regards,$

$Christian$

over 1 year ago

0 Stefan Schauer over 1 year ago

TI__Guru 58641 points

Hi Christian,

thank you for using the E2E forum.

Let me have a look into that and come back in 2-3 days.

Note: you may also check out some of our newer generation devices, e.g. the LM5157 and LM5158.

This also have much more tools for designing the power stage available - e.g. the Quickstart calculator.

Best regards,

Stefan

0 Christian Yanez over 1 year ago in reply to Stefan Schauer

Prodigy 70 points

Hi Stefan,

Thanks for your reply. Actually, I'm using the TPS55332 because I need an automotive step-up IC with a "big" package (soic or some think like that) because I may need to solder it by hand. Also, the device needs to work with low input voltage at least 1.5V, Iout >= 2A peak, Vout = 5V.

If you have any suggestions, I would appreciate your help.

I look forward to hearing from you.

Best regards,

Christian

0 Stefan Schauer over 1 year ago in reply to Christian Yanez

TI__Guru 58641 points

HI Christian,

thanks for the update - will look into that.

Best regards,

Stefan

0 Stefan Schauer over 1 year ago in reply to Stefan Schauer

TI__Guru 58641 points

HI Christian,

for the first formula you need to use the min input voltage as this makes the worst case

Itran is the output load step - is this formula is for the step response

Vodrop is the allow voltage drop when this load step happens.

Best regards,

Stefan

0 Christian Yanez over 1 year ago in reply to Stefan Schauer

Prodigy 70 points

Hi Stefan,

Thanks for your reply,

1.- If I use the minimum input voltage (6V according to the datasheet example), the result is Cccm_min>= 0.59 uF not 0.37 uF, whitch is the data in the datasheet?!

2.- According to the example, what is the value of Itran?

3. Why is fc=10kHz in equation 26?

thanks again.

best regards

+1 Stefan Schauer over 1 year ago in reply to Christian Yanez

TI__Guru 58641 points

Hi Christian,

C_CCM_MIN = 0.5A / 0.52V (1- 6V/25.5V) / 2MHz = 367nF = 0.37uF

Itran is not parameter of the datasheet - this comes from the application requirements

I am not sure what value for I_tran and V_Odroop has been used - i can just back calculate the ratio of both

I assume this was just used as a first estimate, as you can see in 8.2.2.9 later a lower value was evaluated during the compensation.

Best regards,

Stefan

0 Christian Yanez over 1 year ago in reply to Stefan Schauer

Prodigy 70 points

Hi Stefan, thank you very much.

Can I ask you a related last question?

In equation 28, is the term Vi-min the minimum input voltage? In that case the expression (Vi-min - Vo) will be negative and can't take the square root, right?

Thanks again

Best regards

Christian

+1 Stefan Schauer over 1 year ago in reply to Christian Yanez

TI__Guru 58641 points

Hi Christian,

right, this formula does not look to be OK.

Please use the formula for the CI_RMS given in this datasheet instead:

https://www.ti.com/lit/ds/symlink/tps55340.pdf

Best regards,

Stefan

0 Christian Yanez over 1 year ago in reply to Stefan Schauer

Prodigy 70 points

Hi Stefan, thank you very much!

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TPS55332-Q1: Design procedure example and confirmation tool