LMR23630: About LMR23630 Functional Blocks

GARAM AN

Intellectual 1990 points

Part Number: LMR23630

Hello,

I’m looking the LMR23630 datasheet functional blocks, and got some questions.

Could you explain what and how the PFM Detector block works?

Does it affect to change the mode from PWM to PFM? Could you explain detail?

And Can you explain how the Rc and Cc are affected to the compensation?

http://www.ti.com/lit/ds/symlink/lmr23630.pdf

Thank you

over 5 years ago

0 Orlando Murray over 5 years ago

TI__Mastermind 22301 points

Hi Garam,

When the converter is in regulation FB is above the reference and the Error amplifier output is low.

The PFM detector senses the error amplifier output and will reduce the switching frequency when it is low.

Once the error amplifier starts going high again the switching frequency will increase back.

This block is NOT in the FPWM devices.

I'm not sure what your question is with the compensation? It is type-2 compensation, designed for loop stability over entire frequency range and output voltage.

Hope this helps,

-Orlando

0 GARAM AN over 5 years ago in reply to Orlando Murray

TI__Intellectual 1990 points

Thank you Olando,

so, you mean is that even the switching frequency is fixed at 400kHz, when error amplifier output is low, the switching frequency is adjusted automatically.

Is this correct?

Then, is this meaning that the regulation mode is changed automatically from PWM to PFM, when error amplifier output is low.

0 Orlando Murray over 5 years ago in reply to GARAM AN

TI__Mastermind 22301 points

Garam,

The output of the error amplifier is the "COMP" node.

When COMP goes low it will transition into PFM, similar to the figure in your other post (https://e2e.ti.com/support/power-management/f/196/p/869134/3215716#3215716)

If you want constant frequency across the load range you will have to select a FPWM device.

-Orlando

Power management

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LMR23630: About LMR23630 Functional Blocks