LM5176: Buck-Boost behave half switching frequency

Koji Ikeda

Part Number: LM5176

Hello support team,

Customer inquires LM5176 behavior at buck-boost mode. In buck-boost mode, both power stages do switching with half frequency than buck or boost operation. Why does LM5176 set half frequency at buck-boost mode? Does this mean max duty behavior on both buck and boost mode?

Thanks,

Koji Ikeda

over 4 years ago

0 Brigitte over 4 years ago

TI__Guru 65170 points

Hello Koji,

The idea was to keep the inductor current frequency at the same value in buck-boost mode as in buck or boost mode.

0 Koji Ikeda over 4 years ago in reply to Brigitte

TI__Expert 6295 points

Hello Brigitte-san,

Thank you for your support. They have another question. How does LM5176 enter and exit buck-Boost mode (Half switching frequency)? They ask the threshold.

Thanks,

Koji Ikeda

0 Brigitte over 4 years ago in reply to Koji Ikeda

TI__Guru 65170 points

Hello Koji,

There is no threshold. The device will switch in buck mode as long as it can create the output voltage in buck mode. If the input voltage reduces more, then the device will start to add some boost cycles in between and add more and more boost cycles until it is only in boost mode. There is no fixed threshold implemented in the device.

0 Koji Ikeda over 4 years ago in reply to Brigitte

TI__Expert 6295 points

Hello Brigitte-san,

Thank you very much for your support. Do you have any reference data, mode VS input voltage? I assume next, is my understanding correct?

Thanks,

Koji Ikeda

+1 Brigitte over 4 years ago in reply to Koji Ikeda

TI__Guru 65170 points

Hello Koji,

You are correct, but the levels are extremely dependent on the external components used and the layout. If using the quickstart calculator, the efficiency over VIN curve gives an indication.

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LM5176: Buck-Boost behave half switching frequency