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TPS40211

Stephen Taranovich
Intellectual 1330 points
Other Parts Discussed in Thread: TPS40211, TPS40210, TL431, TPS40100
I am considering using the TPS40211 for a renewable energy application to charge a 48VDC battery from a lower voltage input source (10-40V).  In order to limit the charge current, I would probably want to use the TPS40211 in current feedback mode (Fig 29 and 36 of datasheet), but I would also need a way to limit the maximum output voltage.  If I run it in voltage feedback mode, then I need a way to regulate the maximum current.  Also, I am concerned that if the battery is discharged, the TPS40211 will see this as a short circuit and shut down the gate drive, preventing any current from flowing.  Because this is a renewable energy project, I need the maximum efficiency and don't want to add a linear regulator after the TPS40211.
  • 0
    TI__Guru 50635 points

    Stephen,

    Welcome.  I am the lead applications engineer for the TPS40211 controller.  Let me offer a couple of recommendations.

    There are a couple of possible solutions depending on the accuracy of the voltage regulation you need.

    1) If you just need over-voltage protection and it can be fairly course, you can place a zener diode from the output voltage to the feedback pin.  When the output voltage gets high enough for the zener diode to conduct current, it will pull up on the feedback pin and stop switching.  The accuracy of that method will be approximately the accuracy of the zener diode.  You'll want a moderate resistor (1-10k Ohms) between the Feedback pin and your current shunt.  The higher the resistor, the less zener current will flow when you're fully charged but the less accuracy the zener break-down will be.  The Zener will need to pull the FB pin to 260mV to stop switching, so a 10k resistor would need 26uA.  This resistor is necessary even without the voltage protection since it sets the gain of the error amplifiers integrator.

    2) If you need tighter regulation you can use an op-amp powered by the TPS40211's 8V regulator (or other source if available)  The Op-Amp is configured like the tracking amplifier in the TPS40100's datasheeet (TPS40100 has an integrated tracking ramp) however instead of a reference ramp import to the tracking regulator, you can use a TL431 to provide a fixed reference to "track"  The diode connection of this external tracking amplifier prevents it from sinking current from the feedback pin, so it can only reduce the output from the alternate loop.  In this configuration, my recommendation would be to build a constant voltage supply with the TPS40210 and use an external amplifier to build a tracking amplifier for the current sense.  Use a divider from the adjustment pin of the TL431 to generate a voltage lower than its 2.5V reference for the tracking amplifier.  This will allow you to generate a reference voltage for the current control loop less than the TPS40211's 260mV reference.

     

    As for the drained battery condition, if you are using a boost converter topology, there is a diode from the input voltage, through the inductor to the ouptut voltage.  If the input voltage is greater than the ouptut voltage (or battery voltage in this case) the boost converter will not prevent current from flowing from the input to the output.  If you need to limit the current flow into the battery when the input voltage exceeds the battery voltage, you'll need to look for a more exotic power-stage topology such as a flyback, buck-boost or SEPIC.  The same dual voltage/current feedback techniques will work with those topologies.

  • 0
    Prodigy 10 points

    Hello Stephen!

    Is your project still under development? I am working on, I suppose, similar device and I have some experience in that.

    I'm assuming that 48V battery that you mentioned is lead acid battery.

    If you want to charge 48V lead acid battery then the boost topology of DC/DC converter is enough. I used SEPIC (also on TPS40210) which works, but it wasn't necessary.

    Stephen Taranovich said:
    Also, I am concerned that if the battery is discharged, the TPS40211 will see this as a short circuit and shut down the gate drive, preventing any current from flowing.

    I had the same problem, but I didn't know that when battery is deep discharged its internal resistance is quite high and when higher voltage is applied there isn't any short circuit.

    48V battery should be charged to float voltage equal 54,6V (2,275V/cell * 24). Battery should be disconnected from load when its voltage drop below 42V (1,75V/cell).

    Cut-off voltage is higher than your maximum Vin=40V, so you have basically  no need to worry.

    It is, I suppose, an easy way to prevent this even if battery hasn't high resistence, though.

    Let me know, if you still working on this project.

    Regards

    PS. sorry for my english