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Original question:

TPS22916: reverse current protect

TPS22916: TPS22916

Rick Adolf
Intellectual 310 points
Part Number: TPS22916
Other Parts Discussed in Thread: TPS22901, , TPS22912C

i understand that when the device is on that it takes 500mA typical to trigger the RCB circuit. However, when the device is off, what are the conditions for reverse blocking? I want to wire OR two of these devices and one will always be on and the other always off. One has a Vin = 3.3V and the other 1.2V. I'm currently using a TPS22901 and getting reverse current flow which is causing the circuit to fail. Ideally, i'd like to replace the TPS22901's with a footprint compatible device. Note that this is urgent as I need to get working boards to my client in 2 days.

Thanks.

  • 0
    TI__Genius 10855 points

    Hi Rick,

    If the device is OFF, reverse current blocking will be active. Since the TPS22916 has "always-on" reverse current blocking, it can be used in a power muxing application like the one you described.

    The TPS22901 doesn't have reverse current blocking, so it would cause reverse current to flow from VOUT to VIN through the body diode as you described.

    Let me know if you have any questions!

    Thanks,

    Arthur Huang

    To find the latest information on Power Switches, visit www.ti.com/powerswitch

    Please click "This resolved my issue" button if this post answers your question.

  • 0 in reply to Alpha H
    Intellectual 310 points
    Arthur,
    So when the device is off, is there any condition when reverse current can flow or will it always be blocked (when off)? Do any of the reverse current blocking (RCB) specs (Ircb, Trcb,Vrcb,Iin,rcb) apply when off and if so, which ones?

    Thanks,
    Rick
  • 0 in reply to Rick Adolf
    TI__Genius 10855 points
    Hey Rick,

    As long as the input voltage is not floating, the RCB function will operate correctly.

    All of the reverse current specs would apply in this condition. The TPS22916 would require -500mA of current to active (IRCB) and activate in around 10uS (tRCB). The voltage required to release it is VRCB, and the reverse leakage current is IIN, RCB.

    Thanks,
    Arthur
  • 0 in reply to Alpha H
    Intellectual 310 points
    Arthur,
    Does this mean that 499mA of reverse current could flow continuously/forever without triggering the RCB circuit and that it's not until after the reverse current reaches 500mA (typical) that the current is blocked? If hope I'm misunderstanding this spec. I need any reverse current blocked when the device is off.

    Thanks,
    Rick
  • 0 in reply to Rick Adolf
    TI__Genius 10855 points

    Hi Rick,

    Keep in mind that the on-resistance of the device is so small that the RCB circuitry would trigger extremely quick:

    Example:

    (VOUT - VIN) / RON = IRCB

    (VOUT - 5V) / 80mΩ = 500mA

    VOUT = 5.04V

    Therefore, it would only take 40mV for RCB to trigger. Once Vout drops below the VRCB release threshold, then the TPS22916 will stop blocking reverse current.

    Thanks,

    Arthur

  • 0 in reply to Alpha H
    Intellectual 310 points

    Arthur,

    please clarify the blocking mechanism as it's not clear to me if its a current or voltage detect. Is the RCB circuit looking for 40mV or 500mA? I'm concerned that if its a current detect, it actually takes a significant reverse current flow to occur first which may disturb the lower voltage DCDC that's being backdriven by the higher voltage DCDC.

    Also, the dimensions/spec don't appear to be consistent, but maybe i'm missing something. The TPS22916 says that it's a .74x.74mm part, yet the drawing shows .75-.81mm. The TPS22901 says its a .8x.8mm part, yet its drawing shows .73-.79mm. Which numbers are right?

    Thanks,

    Rick 

  • 0 in reply to Rick Adolf
    Intellectual 310 points

    i've used the TPS22912 and TPS22930 for other designs and they appear to only be monitoring for Vout > Vin which i was hoping the TPS22916 duplicated, but it doesn't appear to be the case. Please correct me if i'm wrong. I want to make sure that the reverse current is minimal as i don't know what effect it will have on the two DCDC's that are sourcing the two switches who's outputs are connected. one of the DCDC's is at 1.2V, so the switch needs to work at this voltage plus be footprint compatible with the TPS22901. I'm hoping the TPS22916 is the right choice. If there's a better device, please let me know.

    Thanks.

  • 0 in reply to Rick Adolf
    TI__Genius 10855 points

    Hi Rick, 

    Apologies, I think I'm adding to the confusion. Let me try to explain reverse current blocking differently:

    We have two types of RCB: "always-on RCB", and only when the EN/ON pin is low.

    Devices that contain "always-on RCB" will activate under 2 possible conditions. One if the EN pin is pulled low, and two if the voltage on VOUT higher than VIN by the VRCB or IRCB  threshold. These include devices such as the TPS22916 and TPS22912.

    Devices that only have RCB when the EN/ON pin are low include the TPS22930, as described on the first page of the datasheet: "Reverse Current Protection when Disabled".

    The TPS22916 will operate RCB in the same manner as the TPS22912. Instead of spec'ing the reverse current threshold in terms of voltage like in the TPS22912C datasheet, the TPS22916 RCB spec is in terms of current. However, the behavior is the same, and the TPS22916 will active RCB when VOUT is higher than VIN by 40mV typ.

    To answer your question, we see the TPS22916 and TPS22912 used across a variety of power muxing applications. These devices will work in your muxing application. 

    The TPS22916 is footprint compatible with the TPS22901. Since they have similar landing patterns, you can swap the TPS22901 for the TPS22916.

    Thanks,

    Arthur Huang