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TPS2113A: Confirming connectivity and capacitors required for use in an IoT application

Part Number: TPS2113A
Other Parts Discussed in Thread: TPS2113, TPS22930A, LM66100

Hello

I have an application where I’m using TI’s TPS2113A power mux to select between a battery source (3XAAA) or a USB wall adapter, maximum current will be 1A. We don’t care about nor need the “seamless supply transition” feature, meaning that there is no requirement for the system to maintain power while transitioning from one power source to another. With this in mind, I have the following questions:

  1. The datasheet shows 0.1uF caps at IN1 & IN2 pins, which I’ve added for now in my attached schematic (C7 and C8). For my case, the output of the power mux goes to 2 back-to-back LDOs (3.3V LDO and then 2.8V LDO). Each of those LDOs already has the TI recommended caps at the inputs and outputs. In that case, do I still require the 0.1uF caps at the power mux IN1 and IN2? What’s the impact of removing those caps? I do want a clean power supply but I don’t care about the time it takes to switch from one power supply to another.

  2. If I don’t require the use of the “STAT” pin, what should I do with it? Should I keep it floating or is it safer/recommended to tie it off or ground, either directly or through a resistor?

  3. Just to confirm, this power mux does provide reverse voltage protection? Ie. If the user inserts batteries in reverse polarity, will this power mux protect against damage?

  4. I’m confused about the power rating of the two different packages (SON-8 vs TSSOP-8) on page 2 of the datasheet. Isn’t the power consumed by TPS2113A just a function of the current and the Ron? If my current is set to 1A and Ron is a maximum of 110mOhm, then power will be 0.110 Watts (p=i^2R). Since for most temperatures, SON-8 package power rating is much less than 0.110 Watts (only 2.5mWatt at 25 degrees), does that mean, I must use the TSSOP-8 package, or am I interpreting that table incorrectly?

Thanks,
Berrypower_supply.pdf

  • Hi Berry, 

    Thanks for reaching out on E2E!

    Please find the answers to your questions below:

    1. The input caps help prevent a sudden dip on the input supplies during the inrush current event. Depending on your downstream load, if the load turns on quickly then the input supply might dip. If the LDO can handle the sudden inrush current, then you won't need the caps.
    2. You can keep the ST pin floating or tied to GND using a resistor. 
    3. The TPS2113 does not have reverse polarity protection. You would need to include a diode from the GND path to system GND to prevent reverse voltage from flowing back into the device. 
    4. The dissipation ratings table on page 2 provide a general recommendation on the maximum power dissipation depending on the ambient temperature. You are correct in calculating the power dissipation. As long as you remain below the maximum levels specified in the table, you can use that package version.

    Let me know if you have any questions.

    Thanks,

    Arthur Huang

  • Hi Arthur

    Thanks for the info. To follow up:

    1. The 3.3V LDO I'll be using and shown in the PDF attached to the first post is the TI TLV759 and has "Built-In Soft-Start With Monotonic VOUT Rise".  In that case, I assume the 2x 0.1nF deacaps for the power mux are not required?

    2.  I'll keep floating then.

    3. Could you please double check on this? In this thread, you stated that it does indeed have reverse current protection and will protect against reverse battery polarity and no additional components are required. 

    4. Got it

    Regards,
    Berry

  • Hi Berry, 

    1: What is your load current? If the LDO can handle the sudden spike of current, you should be ok.

    3: Are you referring to "reverse current protection" or "reverse voltage protection". When we mention "reverse current protection", we are referring to if the voltage on VOUT is greater than the voltage on VIN, then no current will flow back from VOUT to VIN. Reverse voltage protection, also known as reverse polarity protection, will protect the device if the GND and VIN are flipped. In the scenario you mentioned, it looks like RPP is required. The TPS2113A doesn't have integrated RPP, and would need a diode from GND to system GND to prevent reverse voltage. 

    Thanks,

    Arthur H.

  • Hi Arthur

     

    Sorry for the delay, as I’m currently out of town and on travel until next week.

     

    1. My current load is max 1A, typical under 500mA.

    3. Here’s my understanding, please correct me if I’m wrong. Typically for a battery powered system with an LDO or a power mux, protection is needed for the following:

           I. Reverse current for the LDO or the power mux itself to protect against the case where output of the LDO/MUX is higher than the input. For LDOs that we have downstream from the power mux , we have a schottky diode with one terminal connected to the output of the LDO and the other to the input of the LDO.

         II. For battery powered devices, there is also a need to protect against the case where the batteries are inadvertently put in reverse, “reverse voltage”, causing current to flow backwards and possibly damaging other ICs. A diode (or MOSFET as switch) is needed on either the power line or ground line to cutoff when such a case is detected.

     

     

    So while the cause for points I and II are different, in both cases there is reverse current. The difference is that in one case, protection is needed for the LDO/mux itself (if not built-in) and the other case, it’s to protect other components.

     

    Based on the above, could you please confirm the following:

    A. Do you agree with my assessment above?

    B. From reading the datasheet, my understanding is that point I above is taken care of by the TI power mux and nothing further is required.

    C. From reading the thread referenced here, where it was specifically asked in the question about polarity protection (voltage), it was stated that nothing further is needed. Therefore, I assume point II is also taken care of. The person in that post was asking about the need to insert a grounded MOSFET (acting as a switch) between the Vbat+ and pin IN2 of the mux (which is connected to battery). Fyi, a grounded MOSFET is used to protect against reverse voltage as an alternative and more efficient solution than a diode,  please see here. Inserting the diode as you suggested (from the GND line to the GND pin of the mux) would be equivalent to putting that diode between the IN2 and Vbat+, or putting a grounded MOSFET as per that other thread.

    Thanks!

  • Hi Arthur

    Can you provide your feedback to my last post?

    Thanks,
    Berry

  • Hi Berry, 

    Apologies from my end as well, I was on timebank last week. 

    I agree with your assessment, a battery powered device should be able to protect against reverse current events as well as a reverse polarity events. As you mentioned, the TPS2113 will protect against reverse current from the LDO / power mux from damaging the battery. 

    However, in respect to reverse polarity protection, the device will need an external MOSFET/diode for reverse polarity protection. I was wrong in the old post, my thoughts were that he was referring to reverse current protection and not reverse polarity protection. I will correct the post, I appreciate the help pointing this out.

    To summarize, you would need to add an external MOSFET or diode for reverse polarity protection.

    Thanks, 

    Arthur

  • Great, thanks for confirming Arthur!

    Regards,
    Berry

  • Sorry Arthur, forgot to ask before marking as resolved, will "TPS22930A" from TI device provide reverse voltage protection (ie. if someone connects battery in reverse)? 

    Thanks,
    Berry

  • Hi Berry, 

    No worries, the TPS22930 does not have integrated reverse polarity protection (ie: a battery is connected backwards). You would need to include a diode on the GND pin that connects to system GND to prevent reverse current from entering the GND pin. 

    We also have a new device with integrated reverse polarity protection, and also comes with reverse current blocking. Would the LM66100 work here?

    Thanks,

    Arthur

  • Thanks Arthur, LM66100 is perfect and exactly matches what I need! Just to confirm, is it in production and currently available?  It shows as unavailable on Digikey and Mouser. 

    Regards,
    Berry

  • Hi Berry, 

    Great, I'm glad the LM66100 will be able to work here! The LM66100 was just released into production about a month ago, if it doesn't show up on Digikey/Mouser then perhaps you could order it from ti.com? I'm not sure when it will appear on Digi/Mouser unfortunately.

    Thanks,

    Arthur

  • Thanks Arthur, yes, I can order it from ti.com