• Author Author: Jan Cumps
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TI SWIFT™︎ Power Module EVM RoadTest: Module Review and Test Setup

Jan Cumps

I'm reviewing a single component DC converter for the TI SWIFTTm Power Module EVM RoadTest.

This article is a review of the switching device and the test setup.

 

Feel free to comment with the tests you'd like to see done with the module.

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The Switching Device TPSM84A21

 

The TPSM84A21TPSM84A21 is a hybrid DC to DC Buck converter. All electronics to make it switch are in the package. It doesn't require external inductors or capacitors to work.

In the simplest setup, no other component is needed. The unit will then switch 8 - 14 V DC to 0.508 V. Maximum current of the output is 10 A.

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When you want to set the output to another value between 0.508 V to 1.35 V,  the only external component is a voltage selector resistor (RSET).

This component is not involved in power conversion and can be a low power small one.

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For ripple reduction, the module has input and output capacitors on board.

If your application is OK with the ripple figures of the device (documented in the datasheet), you don't need external capacitors.

If you need better filtering, you can add input and output capacitors. Guidelines are in that datasheet.

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The device has additional functionality such as Power Good, under-voltage lockout and a possibility to externally synchronise the 4 MHz switching frequency.

Check this functional block diagram for the possibilities.

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The Evaluation Module

 

As expected with hybrid componenst, there's not much more on the evaluation board than the  TPSM84A21TPSM84A21.

The only passives are a set of resistors to select different outputs, and to test the device enable, current limit, sync and power good.

 

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The board gives you good access to all the interesting measure points. It also has footprints for additional capacitors if you want to test such a setup.

For the input and output rails, there are test points very close to the device. They are intended to be probed with an oscilloscope probe with ground spring.

This doesn't work that well with the probes of the Tektronix and Rigol scopes I have.

Their pins are thinker and the distance between center pin and ground spring wider than what the measure point on the PCB takes.

All other test points are solder-on loops that allow easy access with meter test leads or oscilloscope probes.

 

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There's an empty footprint for a coax connector to sync the switcher's clock externally.

 

Test Setup

 

The EVM is connected to an electronic load that draw a current of up to 7.5 A. It can log the current and voltage measured.

The load is connected to the EVM with short thick wires. With these low voltages and high currents, resistance of the wire matters.

I'm using a linear power supply that can deliver more than enough power to feed the EVM at maximum load.

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For measuring, I have a few DMMs and a 4 channel oscilloscope.

 

The PSU, load and oscilloscope are programmable. I can measure and log info in scenarios where the input voltage and output loads change over time.

Things I can automatically log:

  • Current at EVM input and output
  • Voltage at the EVM output
  • Any 4 points that I probe with the scope.

 

Let me know in the comments below if you're interested in particular load operating conditions o the EVM.

I will try the ones that I can perform with the above setup without damaging one of the components.

 

Edit: requests received:

 

 

Related blog
TI SWIFTTm Power Module EVM RoadTest: Module Review and Test Setup
TI SWIFTTm Power Module EVM RoadTest: Noise Measurements
TI SWIFTTm Power Module EVM RoadTest: Efficiency
  • in reply to jc2048

      wrote:

     

    Since you can control both the PSU and the load, you should be able to get very nice curves for the efficiency for a range of different input voltages. It's one area where the automation really pays off. I'd be interested to see you do it, even if your results were the same as everyone else, just to see how you set it up and how involved it was.

    I have this working now, except for logging the data to a speadsheet.

    I made a LabVIEW flow that switches the input power from 8 to 14 V, in steps of 0.5 V.

    For each step, the load draws between 0 and 7.5 A, in steps of 100 mA.

     

    I'll post the results in a blog about the load once I have the logging working. I don't want to post it on the SWIFT switcher blog because the instrument isn't calibrated yet.

     

    image

     

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  • in reply to mcb1

    Mark, sub - 1.2 V is a thing these days image

     

    TI says that suggsted fields of application are:

     

    • Telecom and Wireless Infrastructure

    • Test and Measurement

    • Compact PCI/ PCI Express/ PXI Express

     

    The useful applications I think are those systems where you have high power (up to 10 A)  low voltage requirements and you have an industrial 12 V industrial power rail.

    You can bring the 12 V close to the point of load with reasonable thin copper or wire, then switch down directly at the load.

    I think it's one of those devices where if you don't have a need for it, you don't need it.

     

    Using it in automotive may be odd for the device. It expects fairly narrow range of input voltage (absolute maximum is 15 V) .

    If you have to add components to harden this one for surges and dirty rails as in a car, the component looses its purpose.

  • Great review.

    It's certainly packing some serious hardware into a black blob, and making things very easy.

     

    I'm curious what the intention is for this chip.

    The input voltage range is not within automotive (14v is a bit low), and the Vout upper limit of 3v, makes it a strange supply for processors.

    While I can understand the use for some of the newer 1.5v I/O, the input voltage means some other converter is also required unless you use 3 cells in series (10.8v)

     

    Mark

  • in reply to jc2048

      wrote:

     

    Since you can control both the PSU and the load, you should be able to get very nice curves for the efficiency for a range of different input voltages. It's one area where the automation really pays off. I'd be interested to see you do it, even if your results were the same as everyone else, just to see how you set it up and how involved it was.

     

    Progress:

    image

     

    The PSU cycle from 8 to 14 V is written (except the end clause. It keeps looping)

    For the load, I still have to write the current set block - SCPI command is there but the LabVIEW block isn't written yet.

    I also have to make the "log to spreadsheet" part.

  • in reply to jc2048

    hang on, , I need to build some LabVIEW blocks first.

    Initial results will have to be taken with a grain of salt, because I haven't stabilised the load's behaviour yet.

    If I have my test gear stable, I'll post the results under the road test umbrella. Else under the load's project.