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TPS549D22: how much width of switching trace is enough from switching pin to inductor

Jason Dai
Expert 3720 points
Part Number: TPS549D22

Dear E2E,

Customer is using TPS549D22 to generate 3v3/22A from 12Vin.

In their layout, the width of switching trace from switching pin to inductor is only 67mil.

according to the layout guide, our EVM is 200mil width.

we are not sure if 67mil is ok or not.

BR,

Jason

  • 0
    TI__Expert 3720 points

    Dear E2E,

    Any update?

    BR,

    Jason

  • 0
    TI__Guru 56985 points

    Jason,

    The question of PCB trace width does not have a simple answer because there are a lot of variables that can affect it.  That said, I think 67mils is likely too thin for carrying 22A of load current in the above design.

    1) What is the copper thickness or weight?

    PCB copper thickness can be measured as thickness, typically in mils or microns, or in weight, typically ounces of copper per square foot of PCB area.  Typical thicknesses are 0.5oz, 1.0oz and 2.0oz.

    0.5-oz copper (0.7mils / 18um) has a sheet resistance of 1mOhm / square

    2) How long is the trace from the IC pins to the Inductor terminal?

    The trace above is longer than it is wide, so it will impose multiple squares of loss as the current flows through that copper.

    As a general rule, I would recommend 10-mil wide trace per AMP of current, per ounce of copper weight.

    0.5 oz Copper = 20-mil / Amp

    1.0 oz Copper = 10-mil / Amp

    2.0 oz Copper = 5-mil / Amp

    The TPS549D22EVM uses 2-oz copper weight and 200-mil wide trace to carry 40A DC current.

  • 0 in reply to Peter James Miller
    TI__Expert 3720 points

    Peter,

    The copper thickness is around 2.05mil or 1.46 oz.

    The length from switching pins of IC to inductor is around 270mil.

    Vout is 3v3 and Iout,max is 22A.

    If so, what is minimum trace width on switching path?

    according to the rule you provided, the minimum width is 145 mil. am i right?

    BR,

    Jason

  • 0 in reply to Jason Dai
    TI__Guru 56985 points

    Jason,

    1.46oz copper would need about 6.85-mils / Amp or 150mils for a 22A load current.  About 3.8mm.

    Since the 5 IC pins of the SW node are 2.7mm wide, you may need to fan them out to get to the full 3.8mm

    Alternately, you could use some vias to use a second layer to increase the copper thickness