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TPS2120: TPS2120

Muhammed SÖZER
Prodigy 10 points
Part Number: TPS2120

Hello TI family,

I have two 14.4V DC batteries in my design. I aim that whichever of these two batteries has the higher voltage value, TPS2120 will give it to the output.
The attached design was made according to the TPS2121 infrastructure, but since TPS2121 could not be found in stocks, I am considering moving forward using TPS2120.
When I examined the technical document of the TPS2120 (related section: 10.5 Highest Voltage Operation (VCOMP)), I saw that the R101 in the attached design should be removed and R104 should be short-circuited for the design to work as I wanted. However, when I apply it this way, when the voltage levels of the two batteries are equal (for example, when both are 100% charged, both are 60% charged, etc.), the output voltage becomes 0 (zero) Volt.
How can I solve this problem and my design goal in the fastest and most accurate way by using TPS2120 in my design?
  • 0
    TI__Genius 13260 points

    Hello Muhammed,

    I'd like to confirm first how you're testing this- are you testing on an EVM, custom PCB or through PSPICE?

    Regards,

    Kalin Burnside

  • 0 in reply to Kalin Burnside
    Prodigy 10 points

    Hello Kalin,

    I'm testing on a custom PCB.

    Regards.

  • 0 in reply to Muhammed SÖZER
    TI__Genius 13260 points

    Hello Muhammed,

    Your OV2 pin is set to trigger over voltage protection when IN2 > 6.08V. Is it possible IN1 was slightly above 14.4V and triggered its OV pin as well? it will trigger OV1 protection when IN1 > 14.5V. In that case it should make the output Hi-Z with both OV pins triggered. I'm also concerned about frequent switching with this application- as the batteries discharge they could potentially switch over more often and without seamless switchover you may get frequent undesired output voltage drop. Is there a specific reason you don't want to use priority switching?

    Regards,

    Kalin Burnside

  • 0 in reply to Kalin Burnside
    Prodigy 10 points

    Hello Kalin,

    Thank you for your support. I made changes to the design before your last post. I cancelled the over-voltage protection (OV1 and OV2 pulled down to GND) as the battery voltages would not be greater than 14.4V. But the system still does not work properly.

    In fact, there is no any reason to use priority switching. But I don't have deep knowledge about TPS structure. Could you please help me about priority switching circuit design with two 14.4V batteries by using TPS2120 (max. current consumption is about 1.8A)?

    Best regards.

  • 0 in reply to Muhammed SÖZER
    TI__Genius 13260 points

    Hello Muhammed,

    I have a few comments to make about using TPS2120 in this application.

    Vcomp mode should work in this application. Hysteresis and Vcomp should ensure that IN2 takes priority when the voltages are the same. I would like to see scope shots of both inputs, ST and Vout to see if we can find any indication of what's going wrong with the setup. Also, make sure SEL isn't pulled up.

    If you would like to test out priority switching- it essentially sets a lower voltage using a resistor divider onto PR1 that allows your device to switch from IN1 to IN2 when PR1 drops below 1.06V. If you have significant inrush current- the lower you set your switch over point the more significant the inrush current will be when it switches over. This may or may not be a concern depending on your load conditions.

    If your battery is non-rechargeable this means the device will not switch back to this rail until the comparator sees IN2 is lower than IN1. I'd be worried about you running into the same issue you're currently having at that point so I would recommend testing this condition then too. If it's rechargeable then it may not be a concern. I would recommend setting the switch over point just above the lowest working voltage and observe the switchover event, then do the same when the secondary supply drops.

    Regards,

    Kalin Burnside

  • 0 in reply to Kalin Burnside
    TI__Genius 13260 points

    Hello Muhammed,

    Since it has been two weeks I will be closing this thread. If you still need assistance please make a new thread.

    Regards,

    Kalin Burnside