• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 669 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS63700: Question about Ground Plane use with Non-Isolated Inverter

Harrison Burch
Prodigy 20 points
Part Number: TPS63700
Other Parts Discussed in Thread: TPS7A30, , TPS54160, TPS62125

Hi,

I have a positive Vin rail, and need to generate a negative Vout for use as a power rail with bipolar supply analog components. 

My output needs are:

-10 V > Vout > -16 V   (target Vout is -12 V)

Iout >= 150 mA

Low Ripple/Noise

I will be filtering this switching inverter output with an LDO (TPS7A30) for ripple and noise suppression.

My question is how to implement an inverting buck/boost IC in a non-isolated design when using a system-wide ground plane?

Wouldn't the inverting circuit cause greater issues with ground noise than it's non-inverting equivalent? 

As the analog circuits are rather sensitive (>120dB dynamic range) is it still okay to simply use a ground plane? Would it be detrimental to attempt to filter the switching noise that will be entering the ground plane?

Or should I simply leave ample distance between the inverter and any sensitive circuitry to minimize ground contamination? 

I have tried to find the answer in the many application notes Ti has on inverting buck converters but it seems they mostly describe schematic design and component selection, not potential issues during system integration. 

Regards,

Harrison Burch

  • 0
    TI__Guru**** 150690 points
    Hi Harrison,

    Yes, TPS63700 is a simple device for your power specs, assuming you have a lower input voltage. If you have 12V, for example, then you need a device like TPS54160.

    With a proper layout, the switching currents are kept near the IC such that they have a low impedance path to their sources. This app note, from the product page, discusses the proper layout: www.ti.com/.../slva219a.pdf
  • 0 in reply to Chris Glaser
    Prodigy 20 points
    Hi Chris,

    Thank you for the reply, the app note you linked is indeed very helpful with layout recommendations.

    I have a few more questions on the topic:
    1. I understand good layout minimizes switching noise, but if further reduction is needed could a feed-through capacitor or emifil chip be used directly after the output inductor and before the bulk capacitance to further reduce switch noise?
    2. Does this information apply to any buck converter that might be used in an inverting topology? (Such as the TPS54160 you mentioned, or the TPS62125 or etc). In other words, are there any limitations on using converters in an inverting configuration even if they make no mention of it in the datasheet?
    3. Is there any common-mode content in the output of an inverting buck circuit?

    Thanks,
    Harrison
  • 0 in reply to Harrison Burch
    TI__Guru**** 150690 points
    Yes, you can always use the standard filtering techniques on the output. Ferrite beads, etc. should go after the diode and output cap and be placed on the power plane as it is routed to the load.

    Any buck converter can be used as an inverter, though because of the input voltage requirement, typically mid or wide-Vin bucks are used. Most of these have app notes on their usage.

    Here's a reference design that shows how the data converter team typically filters the output of an inverter. Likely not all of this is required, but this is clean enough for their designs. www.ti.com/.../TIDA-00684