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Ask a question about LT8620

Category: Hardware
Product Number: LT8620
Software Version: None

Hi,

LT8620 is a buck converter, now I want to use it to get an inverted output, the application is as below:

  1. Input: 12-24V
  2. Output: -3V, maximum output current is 800mA

Do you think this is possible? If yes, would you please give me a reference design?

Thanks!

  • Hi,

    Thanks for application of LT8620. 

    LT8620 is suitable for negative output voltage. 

    The circuit below in LTSpice serves as a good reference design to start with.

    Thanks,

    Andrew

  • Hi Andrew,

    Thanks for your answer. I want to ask you other questions.

    1. LT8620 can be used as an inverter converter, ADP5074 is an inverter. What about their input and output noise? Which solution is better? Do you have some technical articles to explain it in details?
    2. Below picture is shown in AN-1168,it says that The sum of the maximum input voltage and the absolute value of the output voltage must be lower than the maximum operation input voltage of the regulators, VMAX which has the typical value of 20 V.This is Why?
  • Hi,

    1. In fact, the efficiency is quite different. At a similar duty cycle and input voltage range, 

    For the ADP5074, the peak efficiency is around 80%.

    For LT8620, the peak efficiency is over 90%.

    Also, the quiescent current of LT8620 is much less and the EMI of LT8620 is better as well.

    2. It looks like that is another part, ADP238x, which has a typical vmax as 20V. That is determined by the internal power mosfet for the max voltage stress on the switches.

    Best regards,

    Andrew

  • Hi Andrew,

    Thanks for your help. I’d like to consult you some other questions.

    1. When using buck converter, Inverted converter, Inverting Buck–Boost, what about their input noise and output noise? Which topology has the best performance? What factors will affect the noise?
    2. In this application note AN-1168, it says that when using the synchronous buck regulator to achieve the inverting buck-boost topology, one common issue that may be observed is that the output voltage ramps up and becomes positive voltage before the regulator starts to work as shown in Figure 8. If an inverted converter is used, such as ADP5074,MAX17577/8,does it have this problem?

    Thanks!

  • Hi,

    1. I mainly work on the buck regulators, so not that familiar with other product lines. To my understandings, the side with the inductor would normally has much smaller noise.

    2. That is good point. LT8620 does not have this issue. For the other parts, I am not sure about that. 

    Best regards,

    Andrew