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TPS22916: Query on Load sharing using Load switch

Sharu N
Prodigy 40 points
Part Number: TPS22916
Other Parts Discussed in Thread: LM66100, TLV7032, TLV1851, TLV1861

Dear Texas Instruments Team,

I hope this message finds you well. I wanted to continue the discussion initiated in [this post], where I'm planning to employ the TPS22916 load switch with reverse current blocking to distribute the load between two batteries.

As I delved into the datasheet for the  TPS22916, a particular specification caught my attention—the Activation current (IRCB), denoted as -500 mA (typical). In our application scenario, we anticipate a current draw within the range of 50 to 100 mA. With this context in mind, I'm seeking clarification on whether the "Always-ON true Reverse Current Blocking (RCB)" feature will effectively perform under these operating conditions.

Your insights and guidance on this matter would be greatly appreciated as we proceed with the implementation of this load switch in our project.

Warm regards,
Sharu

  • 0
    TI__Mastermind 19910 points

    Hi Sharu,

    Thanks for reaching out and following up on this post. I'll look to see if there are any ways to activate RCB at 50mA or below.

    When the device is disabled, RCB is always on - is there any way you can use this piece of information?

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 40 points

    Hello Patrick,

    Upon reviewing the application schematic below that we discussed in the previous thread, it appears that the TPS22916 may not be disabled as intended due to the fact that it's pulled up.

    Best regards,
    Sharu

  • 0 in reply to Sharu N
    TI__Mastermind 19910 points

    Hi Sharu,

    What about using a comparator between VOUT and VIN of each TPS22916 to detect when VOUT > VIN and disable the ON pin?

    A short search results in:

    TLV1812 (dual channel, no hysteresis)

    TLV1851 (single channel, 2.8mV hysteresis / 2 = .0014V / .06Ohm = 23mA disable current)

    TLV7032 (dual channel, 10mV hysteresis / 2 = .005V / .06Ohm = 83mA disable current, cheapest 1ku price)

    Is using one of these an option for you?

    Please let me know if more elaboration is needed.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 40 points

    Hi Patrick,

    That should work.

    But then wouldn't it be simpler to use LM66100 like below where it would continuously provide output power?



    Or do you see any drawbacks to this compared to the load switch with a comparator circuit?

    Best regards,
    Sharu

  • 0 in reply to Sharu N
    TI__Mastermind 19910 points

    Hi Sharu,

    Yes, in that case it would be simpler to use the LM66100, but the advantage of the load switch + comparator is that it allows for both batteries to provide power simultaneously whereas the LM66100 would only allow one battery to be active at a time. I believe that in this scenario it comes down to how well your application tolerates one battery being active at a time/relatively frequent switching between batteries vs. cost/complexity.

    Let me know if you have any questions you have that would help better understand the tradeoffs.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 40 points

    Hello Patrick,

    Upon careful consideration, the combination of a load switch and a comparator does indeed appear to be the more suitable choice for our application. I conducted a preliminary simulation, albeit without considering hysteresis, to observe the behavior of the comparator. It came to my attention that the voltage at the V+ input must be higher than both IN+ and IN- for the comparator to operate as intended.


    However, the challenge I'm facing is that I cannot provide a constant high voltage at V+ since this circuit is responsible for powering all subsequent components.

    I find myself stuck in this regard, and I would greatly appreciate any insights or feedback you can provide regarding this matter.

    Thank you for your assistance.

    Regards,
    Sharu

  • 0 in reply to Sharu N
    TI__Mastermind 19910 points

    Hi Sharu,

    I see on the TLV7032 data sheet that IN+/- can be up to 100mV higher than V+/lower than V-.

    It is similar on TLV1812 (rail-to-rail +/-200mV) and TLV1851 (IN+/- can be from -0.1V to 40V independent of V+).

    If using TLV1851 (or another comparator where IN can be higher than V+), then you should just be able to use VIN1/VIN2 to power it without worrying about VOUT being higher.

    Does this help?

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 40 points

    Hello Patrick,

    Indeed, the utilization of the TLV1861 appears to be a viable solution to address the previously discussed issue.

    I would appreciate it if you could verify the feasibility of the simplified setup outlined below:

    Furthermore, I have noticed that the TLV1861 incorporates an internal hysteresis of 2.7mV. While this internal hysteresis can be advantageous in mitigating noise-induced chatter, I would like to inquire if, based on your expertise, you believe that introducing external hysteresis to the circuit would be necessary for its optimal functionality. It is important to note that all the calculations provided by TI have been predicated on the assumption of a constant voltage source.

    Your insights and recommendations on this matter would be greatly appreciated.

    Thank you for your assistance.

    Regards,
    Sharu

  • +1 in reply to Sharu N
    TI__Mastermind 19910 points

    Hi Sharu,

    Yes, it looks like the circuit in the picture you sent would work well. I calculate that the respective TPS22916 will be disabled when only (0.0028 / 2 = 0.0014V / (2 * 0.6) = 11.7mA) of current flows from the higher to the lower voltage battery.

    Also, with respect to the hysteresis, it looks like the hysteresis is evenly split between the "rising" and "falling" thresholds, instead of being fully on the "falling" threshold - please see the picture below from Section 7.4.2 of the data sheet for a better description (this is why I divided the hysteresis in half while finding the reverse current at time of disable).

    If the operating conditions end up creating noise issues, I would recommend increasing the amount of input capacitance rather than adding external hysteresis, as adding additional hysteresis on the "rising" (red in picture) trigger will increase the amount of current that will flow between batteries before the TPS22916 disables and adding additional hysteresis on the "falling" (black in picture) trigger could cause both TPS22916s to be disabled at the same time. However, adding additional hysteresis to the "rising" trigger is still an option, and given that the batteries are rechargeable the additional reverse current flow may not be a huge problem.

    Please let me know if I can be of any more assistance.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 40 points

    Hi Patrick,

    Nothing else as of now. 
    Thank you, Patrick 

    Best regards,
    Sharu