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PTH12040W: Operating as a current source

Victor Marten
Prodigy 60 points
Part Number: PTH12040W
Other Parts Discussed in Thread: PTH08T255W

Several posts (going back as far as 2011) mention operation of the PTH12040W as a current source.

Control of the current is achieved via the Auto-Track pin, presumably for the resulting output voltage that is less than the value set via the Vo-adjust pin.

While the posters mention that they've operated the module as a current source "for years", there were comments by the TI stuff that did not endorse this mode of operations.

Question 1: would it be appropriate to use the PTH12040W module as a 40-50 A dc current source?

The load is very "benign" and stable, purely resistive of some 2-5 milliOhms (i.e. output voltage would have to be between 100 mV and 250 mV, much less than the stated minimum set voltage of 0.8 V). No load transients at all, and the control loop to Auto-track pin would be very slow. Efficiency does not need to be as high as for the rated minimum output, even 30-40 % would be acceptable. Input supply voltage is 12 Vdc.

Stated differently --- would it be possible to set the output voltage to a (relatively) stable 100 mV to 250 mV level using the Auto-track pin, and operate the module continuously?

The module will be cooled by a dedicated fan, with sufficient airflow.

Question 2: When Auto-track pin is used for controlling the output voltage, and the voltage is very low, does the controller exercises all (presumably three, based on the number of inductors) phases? Or does it employ "phase shedding" and only a single phase is switching?

This is related to the maximum current ripple that the module will produce when operated as a current source. The multi-phase units tend to have smaller current ripples than a single- or double-phase (such as  PTH08T255w) modules.

Question 3: When operated as a current source into a low-Ohmic load, does the module need any capacitance at the output?

Likewise, can the input capacitance be reduced, considering the fact that the load is very stable and there are no transients?

Finally: if PTH12040W module would not be a good candidate as a current source -- can you suggest and alternate TI module that would indeed be suitable?

  • 0
    TI__Mastermind 38230 points

    Victor :

    PTH012040W  is not recommended for this control current application  nor can we indorse this application.  PTH12040W buck regulator   absolute   minimum output voltage is 0.8V.

    Tom  

  • 0 in reply to Tom Guerin
    Prodigy 60 points
    Hello Tom,

    Would it be possible to get the part number for the controller used on this (PTH012040W) POLA compatible module?

    In general, operations near 0 V output should not overstress "Synch Rectifier"-output buck converters too much. Just a couple of percent of more power dissipation in the SR MOSFET, that's all. That's why the PTH012040W module looks so good for an application like this... Judging by the minimum On-time (from the datasheet), it should be able to handle the 0 V output condition without any issues, and even NOT produce a lot of ripple.

    Also -- could you suggest any part numbers for modules specifically capable of 50 A dc current-source functionality into near Zero load?

    Thank you very much!
  • 0 in reply to Victor Marten
    TI__Mastermind 38230 points

    Victor:

    Any further question can be sent to me directly  at tguerin@ti.com

    . The switching DC will all operations at < 0.8Vminimum .

    tom