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TPS22912C: Reverse current protection in TPS22912C

Andy Sarangi
Intellectual 270 points
Part Number: TPS22912C
Other Parts Discussed in Thread: TPS22953, TPS22910A

Hi,

I've two different 5V supplies (say 5VA and 5VB) in the system and depending on which one is available or in case of when both 5VA and 5VB supplies are available I use one 5V supply to charge the battery at 1A. I use two TPS22912C switches, and output of two switches are shorted: say 5V_Charger_IN as the output. supply name to charge the battery.

ON pin of both switches are tied to its 5V input supply with a 100K pull down. Suppose 5VA is the stronger 5V supply with 3A rating, 5VB is rated as 1A. Do I need to add an additional  1Amp rated diode in 5VB switch input path to fully block reverse current from 5V_Charger_IN or can I depend on TPS22912C to the full reverse current protection and  no reverse current will flow back into 5VB input path? Kindly advise.

- Andy

  • 0
    TI__Genius 10855 points

    Hi Andy, 

    It seems like you're trying to connect both TPS22912C in a Power Mux configuration, where both input voltage rails are routed to a single output rail. The Reverse current protection feature will prevent any current from flowing back into 5VB. However, the TPS22912C is not rated for 3A applications, not sure if you were just giving an example or this is the actual values you will be using.

    I would recommend taking a look at this app note on Power Muxing using Load Switches/eFuses. Your set up is similar to the one shown on page 4, only difference is that the app note uses a TPS22910A alongside the TPS22912C for manual switching. If you need 3A of current, try taking a look at the circuit on page 7 using TPS22953.

    Let me know if you have any questions,

    Arthur Huang

  • 0 in reply to Alpha H
    Intellectual 270 points
    Hi Arthur,
    I know TPS22912C is a 2A rated switch; even though 5VA is 3A supply, output rail (battery charger) only needs 1A (1.5Max). Will there be problem here to use TPS22912C to provide the supply output?

    I can use the high & low side switches like the app note suggests but I can't have a manual switch / GPIO. Will there be any problem if I use 10K pull-up at the ON pin to VIN1 supply to turn it on when it is available and the low side switch will have a 100K pull down to gnd at the ON pin, so we have 10K and 100K voltage divider at the ON pin , most of the time low switch with VIN2 is on and when VIN1 is present the high side on switch will kick in with 10K pulling it at the ON pin allowing TPS22912C be on and the TPS22910A will be off. Will this work effectively? Please confirm. Thanks,

    Andy
  • 0 in reply to Andy Sarangi
    TI__Genius 10855 points

    Hi Andy,

    The TPS22912C should be fine if there's only 1A/ 1.5A max output.

    I'm assuming the configuration you're describing looks similar to this, (sorry bottom resistor should be 100k):

     

    Unfortunately, a setup like this would not work. While the reverse current feature is enabled, there needs to be a voltage differential between VOUT and VIN. If VIN1 is disconnected, it will follow the value of VOUT, potentially causing a feedback loop on the enable. Another issue is forcing VIN1 to GND. If VIN1 is grounded, any pulses on VOUT will trigger VIN to follow, potentially enabling the pin again. Here are two links to other E2E posts where similar issues were discussed: 

    1: Power Mux with VIN Disconnected

    2: Power Mux with VIN Grounded

    As a solution, please take a look at page 7 of the app note using the TPS22953. This circuit seems to be very similar to the one you described. The setup has automatic switchover if a power supply fails or is removed, and there is no enable pin or manual toggling required.

    Thanks,

    Arthur

  • 0 in reply to Alpha H
    Intellectual 270 points

    Thanks Arthur, I've space issue on the board so wanted to keep it simple and that's the reason wanted to stay with a simall switch. Will this approach work, which I was originally thinking:

    Please see the attachment.

    tps22912C-5V-use-case.pdf

  • 0 in reply to Alpha H
    TI__Genius 10855 points

    Hi Andy, 

    Unfortunately, I do not think this circuit will perform as expected. The two issues I stated above will still be an issue; we generally do not suggest connecting the enable pin of the switch to VIN due to unexpected results. 

    There's also another issue I forgot to mention.

    The TPS22912C will power down faster than the start-up sequence. It takes typically around 840 µs for the TPS22912C to turn-on, while the turn-off time can be as fast as 6.6 µs. When you switch the first 912C off and turn on the second 912C, there will be a brief period of time where the first switch is off while the second switch is still turning on. Since both of your voltage rails are operating at 5V, the output voltage might dip beyond an acceptable range.

    Another suggestion is the integrated TPS2215 Power Mux. This device can automatically switch between channels, but the device can only support up to 1A per channel. 

    Thanks,

    Arthur

  • 0 in reply to Alpha H
    Intellectual 270 points

    Thank you Arthur for outlining all the issues, greatly appreciate your help. Will use power-mux TPS2215 or 2113. 

    - Andy