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TPS62360 VIN and AVIN difference

Matt Shira
Expert 2180 points
Other Parts Discussed in Thread: TPS62360, INA219

Hi,

TPS62360 datasheet SLVSAU9C ties VIN and AVIN together on the 1st page, yet optionally put a 10Ohm low-pass filtering resistor on page 31 (fig 49) for noisy supplies.

1. The "functional block diagram" on page 9 shows AVIN is connected to a "Analog Circuit Supply" block, yet little information is found in the DS for this block. Could someone give a few comments on the purpose of this block, and the difference between VIN and AVIN? For example, is the Analog Circuit Supply modules used for "DCS-Control" or "remote sensing"?

1. From the use of 10ohm as LPF, it seems that the current goes into VIN is expected to be small (or efficiency would get very low). VIN and AVIN pins are tied together, and does this clue suggests that the VIN is the main power supply, and a much larger amount of current goes into VIN as compared to AVIN?

 

Matt

 

  • 0
    TI__Guru**** 151290 points

    Thank you for using an excellent title for your post.

    Your question relates more generally to many converters which have separate pins or supplies for the power stage and quiet circuits.  This is the same concept as analog and power ground, which I recently discusssed here: http://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/t/295232.aspx

    From the block diagram, you can see that the VIN pin goes to the high-side MOSFET.  This is where the switching current goes.  This current will be very high, up to 3-4A peak.  No resistance should ever be placed here.

    The AVIN goes to everything else in the IC--it is used to power the IC.  This pin basically draws the Iq, which is in the uA range.  Many engineers are used to putting a LPF filter on such pins but it is not required for the TPS62360.

  • 0 in reply to Chris Glaser
    Expert 2180 points

    Thanks. We are still looking at that.

    Another inquiry is does TPS62360 has the ability to read the load current from I2C? If so then it would have the ability like current monitoring IC INA219. Since it has I2C interface, I wish it could have the ability.

    However register lists seems contain no such mentioning?

     

    Matt

  • 0 in reply to Chris Glaser
    Expert 2180 points

    Additionally, if the load of TPS62360 is small (~200mA), and is of very low frequency, would we have more liberty in the layout?

    Asking this because there seems to be so many restrictions in the "PCB Layout" section.

     

    Matt

  • 0 in reply to Matt Shira
    TI__Guru**** 151290 points

    PCB layout is extremely important in switching power supplies.  The D/S outlines the best way to do it.  I don't see a reason why you would prefer to do a non-optimal layout.

    There is not a load current monitoring function in the TPS62360.

  • 0 in reply to Chris Glaser
    Expert 2180 points

    Chris,

    Figure 11 of TPS6236xEVM UG SLVU425A shows a thermal image board. One of our colleague mentioned that such results might be derived from simulation software like Mentor FloTherm before actually making the board.

    Regarding the"non-optimal layout" comment:

    Predicting the behavior of EM fields in copper (waveguide) and board dielectric is a challenging task which might require solving Maxwell equations, calculating reflections at copper boundary, plus analyzing the thermal performance. Doing these in their full extent requires very powerful workstation or supercomputer. Are these power supply IC EVM designs the result of these computer simulations, or simply the trial-and-error product of experienced engineers?

     

    Matt

  • 0 in reply to Matt Shira
    TI__Guru**** 151290 points

    You're making this far more complicated than it is :)

    The thermal image is of a real PCB.

    And no, you don't need to use complicated software tools to extract impedances, etc.  The layout guidelines come foremost from the EVM design which 'works'.  It is a known good design, following good power supply design techniques.

  • 0 in reply to Chris Glaser
    Expert 2180 points

    Chris,

    Thanks for your very helpful answer!

     

    Matt

  • 0 in reply to Chris Glaser
    Expert 2180 points

    Chris,

    Does the "IR-Drop" mentioned repeatedly in TPS62360 datasheet refer to the voltage drop due to high resistance on the wire? Does it actually mean deltaV=I×R drop, as been described in the Wiki article:

    "Due to the resistance of the interconnects constituting the network, there is a voltage drop across the network, commonly referred to as the IR-drop."

     

    Matt

  • 0 in reply to Matt Shira
    TI__Guru**** 151290 points

    IR drop means V=IR.  The R can come from anything, wire, IC, PCB, etc.