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TPS54302: pulse skipping mode question

Pedro Parodi Ramirez
Prodigy 90 points

Part Number: TPS54302

Hi there.

I have a question about using the TPS54302 step-down converter with light loads.

In my design I was originally using the TPS6217 (up to 500mA) wich was okay for my circuit (not tested, just designing schematics and PCB). But chip is out of stock in DigiKey and it's expensive on China market so I wanted to change it.

The main thing about the TPS54302 model is that under 500mA loads enters in Eco-mode (pulse skipping) and I'm not sure about it's consequences.

I have a design wich consumes 150mA top. The step down converter will mainly use to power a 5V sensor and as a Vin for 3.3 linear regulator (MCP1702).

The regulator powers MSP430FG6047 uC and other things.

 

Could I expect problems by using the TPS54302 continusly in pulse skipping mode? The idea it's to power the all system with 12V and 24V. The converter fix an 5V output and then the regulator a 3.3V.

Will the 3.3V linear regulator function properly?

Any tip or comment about this would be appreciated.

Thank you!!

  • 0
    TI__Mastermind 36461 points

    Hi,

    I will help on this after this weekend.

    BRs

    Lucia

  • 0
    TI__Mastermind 36461 points

    Hi,

    With regard to your question,

    1.When you use TPS54302 in eco-mode, the efficiency will be lower. But it will not affect the normal operation of the chip.

    2. For  TPS54302, when the peak inductor current is lower than 500 mA (typical), the device enters pulse-skipping mode. But it does not mean under 500mA loads it will enter eco-mode.

    Could I double check two things with you?

    1. What is the output current of your design? Do you mean the max loading is 150mA or what is it's nominal current?

    2.What is the value of the inductor? And what is your input voltage?  So that I can check whether it enters eco-mode for you.

    Does it make sense to you? Or if you have any other questions, please feel free to let me know.

    Best regards

    Lucia

  • 0 in reply to Lucia Gao
    Prodigy 90 points

    Hi there.

    1. The peak current of the design is 150mA approx. As the nominal value, it should be around 40mA.

    2. The inductor i'm using is 10uH, according to datasheet recommendation. Using datasheet equations to calculate inductor value for 40mA output current, the value is closed to 1mH (too high).

    My main question would be:

    1) Pulse skipping mode will increase the current ripple. Will this affect a linear 3.3V regulator (MCP1702)?

    2) If the converter enter in discontinous mode, will the linear regulator be affected by the fact that instantaneously the current in reaching zero?

    Thank you for your time.

    Best Regards,

    Pedro.

  • 0 in reply to Pedro Parodi Ramirez
    TI__Mastermind 36461 points

    Hi Pedro,

    1) It will increase the inductor current ripple, but its output current is stable. It will not affect 3.3V regulator. It is suggested to check whether your output voltage range is between 2.7V to 13.2V which is MCP1702 input voltage range since output voltage ripple would be large in eco-mode.

    2) It will not be affected because of discontinuous mode.

    Best regards

    Lucia

  • 0 in reply to Lucia Gao
    Prodigy 90 points

    Hi Lucia.

    Thanks again for your time.

    Input for the converter will be 24V as standard but also 12V occationally. The output will be fixed to 5V. Could you help me with the inductor selection?

    1) With 24V and switching frecuency of 290kHz (worst case) and a load of 40mA I get 170uH as minimun value for the inductor. It is a reasonable value?

    2) The inductor should be SMD but I don't know wich are the standard packages and values. Is there any recomendation in this regard?

    Regards,

    Pedro.

  • 0 in reply to Pedro Parodi Ramirez
    TI__Mastermind 36461 points

    Hi Pedro,

    1) You can find recommended component value below.

    2) You can find about standard packages information in some manufacture website like Wurth Elektronik

    Passive Components | Catalog | Würth Elektronik Product Catalog (we-online.com)

    Best regards

    Lucia