LMZM33603: About Inverting buck-boost (IBB) topology

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Guru 21045 points

Part Number: LMZM33603

Hi Team,

I would like to use LMZM33603 for Inverting buck-boost (IBB) topology.

Then, I understand that I can connect PGND pin and AGND pin.

Because, the device has AGND and PGND are internally tied in this device.

Please refer to the following E2E thread.

https://e2e.ti.com/support/power-management/f/196/t/754416?tisearch=e2e-quicksearch&keymatch=LMZM33603

Is my understanding correct?

And, could you please let us know if you have any concern?

[Supplementary explanation]

By the way, according to datasheet, “Do not connect this pin to PGND”.

This comment is advice for normal operation(buck topology).

Therefore, I understand that it is not applicable in IBB topology.

Regards,

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over 4 years ago

0 Neal Zhang over 4 years ago

TI__Expert 4720 points

Hi Hide,

The recommendation that not connect AGND to PGND is to reduce noise, as your attached discussion.

Inverting buck-boost has no difference. You don't need to connect them externally.

0 Hide over 4 years ago in reply to Neal Zhang

Guru 21045 points

Hi Neal-san,

Thank you for your prompt reply.

I understand that PGND connect to negative VOUT and AGND connect to Analog GND on board.

And, this circuit does not have any problem even if the device has AGND and PGND are internally tied in this device.

Is my understanding correct?

If yes, I have one more question.

I guess that unnecessary current occurs in the device.

(From Analog GND (0V) to Negative VOUT(less than 0V).

Does this current not have any problem?

Regards,

Hide

0 Neal Zhang over 4 years ago in reply to Hide

TI__Expert 4720 points

Hi Hide,

In your application, both the "IC AGND pin" and "IC PGND pin" should connect to the "system Vout".

For your question, I think you want to know if it is needed to connect "IC AGND pin" and "IC PGND pin" externally on pcb board, right? The answer is you don't have to, because they are connected in the IC, and then both of them will connect to the "system Vout".

Hope it helps.

0 Hide over 4 years ago in reply to Neal Zhang

Guru 21045 points

Hi Neal-san,

Your recognition(my question ) is right.

And, I'm sorry to confuse you.

I understand that both the "IC AGND pin" and "IC PGND pin" should connect to the "system Vout" in IBB topology.

(Please refer to the following circuit.)

Regards,

Hide

0 Marshall_Beck over 4 years ago in reply to Hide

TI__Mastermind 29670 points

Hide, let us know if you need more assistance.

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LMZM33603: About Inverting buck-boost (IBB) topology