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LM20343EVAL: Inverting the output voltage of LM20343EVAL

Mohammad Alsmadi
Intellectual 340 points
Part Number: LM20343EVAL

Hello,

I am writing to inquire if I can get an inverted output voltage from the LM20343eval (Converting to inverting buck-boost). To my understanding, I should connect J3 with J2 and get the output voltage with a positive terminal at J4 and a negative terminal at the merged (J2 and J3), is this right? and how can this affect the conversion ratio? will it follow the conversion ratio of the inverting buck-boost (-D/1-D)?

Thank you 

  • 0
    TI__Mastermind 25590 points

    Mohammad,

    You can find lots of information in this app note and this app note. Connecting J2 to J3 will short the output. Refer to those app notes for the necessary modifications.

    -Sam

  • 0 in reply to Samuel Jaffe
    Intellectual 340 points

    Thank you, Sam! I will refer to the mentioned app notes. Once I do the recommended modifications to make an inverting buck-boost, the conversion ratio will be modified accordingly from (Vout/Vin=D) to (Vout/Vin=-D/(1-D)), right?

  • 0 in reply to Mohammad Alsmadi
    Intellectual 340 points

    Hello Sam, I would like add one more question here, please! I appreciate your great help.

    Could you please give me a simple procedure to invert the output voltage of the LM20343Eval? I read the App. note and I got confused, actually. I know this should not be difficult but I actually still did not get it well. So far, I understand that I need to connect a capacitor between J1 and J3. If this is correct, please tell me what else I need to do, PLEASE!

    Thank you so much in advance. 

  • 0 in reply to Mohammad Alsmadi
    TI__Mastermind 25590 points

    Mohammad,

    For this EVM you might be able to get away with simply connecting VSUPPLY+ to VIN (J1) and connecting VSUPPLY- to VOUT (J3). That will turn VOUT into "GND" and GND into "-VOUT" but, as you said, I'd recommend a cap between J1 and J3 (22uF is good). Put a current limit on the supply for your first tests.

    And yes, the new conversion ratio is: Duty = VOUT / (VIN + VOUT)

    Keep in mind the device must be rated for VIN - (-VOUT) so 15VIN, -12VOUT should be fine. 24VIN to -12VOUT is maxed out.

    -Sam