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TPS6507x: thin traces for VDCDCx and FB_WLED pins?

Anonymous
Anonymous
Guru 17045 points

Hi,

I would like to ask a question on TPS6507x VDCDCx and Lx pins.

In Are TPS65070 "Switch" pins output pins?, Daniel Acevedo referred to two application notes for the principle of buck/boost converters:

[1] http://www.ti.com/lit/an/slva057/slva057.pdf

[2] http://www.ti.com/lit/an/slva061/slva061.pdf

However, the circuitry for feedback sense input was not shown in either document.

For each DCDC output, either buck {1, 2, 3} or boost {LED, 4}, there is a switch pin Lx as well as a feedback sense input VDCDCx:

  1. Does the 2.2uH inductor in TPS6507x application circuit example correspond to inductor L in Fig. 1 of [1], as attached below?
  2. The feedback circuitry was NOT shown in [1] or [2]. However, I guess that they might draw very small current and work like using the sensed voltage to for controlling gate of Power MOSFET Q1?

The actual question is about track width: Should Lx or VDCDCx use wider traces?

In TPS6507x EVM I see only Lx pins have wider traces; in EVMAM1808, both Lx and VDCDCx have wider traces.

If VDCDCx pins are used for voltage sensing, then there should be negligible current passing through it so that wide trace is not necessary. Are the wide traces in EVMAM1808 for VDCDCx pins unnecessary?

And may I also use thin traces for connecting to FB_WLED, since it is also voltage sensing input which is not supposed to carry supply current (or return), but only with negligible current?

 

Zheng

  • Traces for Lx must be wide and short. Traces for VDCDCx must be short. FB_wLED can be routed longer distances and can be >=8 mils but needs to be routed clear of any high noise sources.
  • Anonymous
    0 Anonymous in reply to Daniel Acevedo

    Daniel,

    Daniel Acevedo said:

    Traces for VDCDCx must be short.

    I think this basically means low resistance (hence voltage drop). If my trace connecting to VDCDCx has a calculated resistance of 0.02Ω, would it be fine?

    Zheng