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LM51581-Q1: Question about configuring the peripheral components and simulation

Part Number: LM51581-Q1
Other Parts Discussed in Thread: INA849

Hello everyone. This is my first time posting on this forum... I am a senior student in college working with two other guys on a capstone design project and we have some difficulties in our power supplies. Our project is a microphone preamplifier involving INA849. The core amplifier was simulated and producing good frequency response plot and good SNR. We moved on to designing the driver for phantom power, which is a 48V power supply that will conjunctly feed into the input of INA849. A standalone 48V power supply seemed expensive and violated our principle of designing a cheap but still relatively high fidelity preamplifier. So I searched online and learned that a DC-DC boost converter would do the job of converting 15V (which will be provided by an AC-DC converter LD05-23B15R2) to 48V. Our goal is to use the provided 15V to produce 48V used for phantom power. I see that there exists a quick-start calculator, which is quite helpful since we only need to feed input into it. My intended specialization is in the field of digital VLSI, and I only have a vague understanding that DC-DC converters use PWM signals to control the switches to boost up the voltage... The following configurations are the result me and my teammate tinkering for some time:

My classmate produced the loop compensation part and I was responsible for all other parts. Does this look like an okay configuration or a disastrously wrong configuration that guarantees an explosion? Where can I learn more about how to use this chip? Is this chip even necessary for our design?

Sorry for asking so many questions... Our critical design review is coming up and we were spending too much time on learning what preamp is and debugging cadence simulation on the core amplifier part.

  • Hi Zhipeng,

    This design looks OK for the described application.

    A few things to consider when doing a first design on SMPS.

    - take enough margin for the selected components (e.g. Caps on the output side will be good to have >30% better 50%) 

    - consider the saturation current of the inductor I L,Pk

    - take care about the layout and check your current loops. This should be as small as possible.

    To get an understanding of the basics for DC/DC converter (Boost Topology) i can recommend this paper:

    Topic_3_Lynch.pdf (

    Best regards,


  • Hi Stefan,

    Very thankful for your response on the validity of the design, and thanks for the paper recommended. The margin is respect to the "minimum/maximum capacitor value", right? From reading typical phantom power current draw list online, the DC/DC converter would probably be drawn for maximum of 10mA, would the inductor be driven to saturation? And for the current loop, by small do you mean the current going through the loop should be small?

    I put the circuit into cadence virtuoso but the spectre simulation does not yield and useful results... We are kind of stuck at this stage because we would love to make sure it will produce reasonable output first before buying the parts and build physical implementation to our amplifier... Do I post the simulation question here on TI forum, or do I need to go and ask Cadence people about how to simulate it?

    Again, thank you for your support. I will read the paper thoroughly and get more understanding on this topic.


    Zhipeng Fan

  • Hi Zhipeng,

    the important rating for the Capacitor is the voltage rating. Check the max voltage on the capacitor and add the margin here.

    The current loop is the area on the PCB which is enclosed by the current path to the load and back from the load.

    - This needs be done for both phases (Switch closed and switch open)

    For Cadence virtuoso I can not help, as i do not know this tool. May you ask at Cadence for some help.

    Best regards,