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TPS2553: Overvoltage protection doesn't work

Shareef Jalloq7
Prodigy 80 points
Part Number: TPS2553
Other Parts Discussed in Thread: TPS25221

Hi there,

we've used the TPS2553DRV in at least two designs that I've tested now.  Applying 5.5V to the output pin while the device is enabled doesn't cause the device to turn off or pull the FAULT# pin low.  Instead I can happily feed the overvoltage back up through our power tree.

I'm testing this in circuit by using a jumper wire from EN to 3V3 and then applying a voltage of 5V5+ on the output.

Thanks.

  • 0
    TI__Expert 8420 points
    Hi Shareef,
    I think you want to test the reverser voltage protection feature. For these protection feature device need to meet two condition : 1) Vout above Vin 135mV ( which you can use oscilloscope to capture); 2) Vout > Vin (135mV) period should longer than 4mS . The issue you haven't see the fault pin pull low is above tow condition haven't met . One suggestion is use a big resisor in parallel input cap to discharge the input voltage , as the output will charege up the input cap voltage in very short time (less than 4mS).
  • 0 in reply to Michael Tan
    Prodigy 80 points

    Hi Michael,

    yes, I fully understand the conditions for which the reverse voltage protection should be working.  Which is why I opened this ticket.  The input is 5V and as my ticket suggests, I can apply 5.5V and not have the protection function work.  I tried with 6.5V as well just to be sure.

    I don't understand your suggestion of adding an extra resistor in parallel with the input cap.  Surely the protection circuit should function correctly without extra components not detailed in the data sheet?

    Shareef.

  • 0 in reply to Shareef Jalloq7
    TI__Expert 8420 points
    Hi Shareef,
    You have apply 5.5V at output and input is 5V , so Vout is above Vin 0.5V that meed the first condition (Vout should above Vin 135mV) .
    The second condition is Vout > Vin time period should longer than 4mS. I suspect the second condition haven't met , that is why I suggest you to use a external loading resistor to discharge the Vin voltage make sure time is longer than 4mS.
    Vout will charge up the Vin voltage very very fast, when vin charge up the voltage will equal to vout .
  • 0 in reply to Michael Tan
    Prodigy 80 points

    OK, perhaps I'm not understanding the feature.  I assumed that the reverse voltage protection was designed to protect any upstream regulators from this fault condition.  But you're saying this feature doesn't work under normal operating conditions unless you add a loading resistor to slow the rise time on the input voltage.  Shouldn't this information be detailed in the data sheet and the typical application sections be updated?

  • 0 in reply to Shareef Jalloq7
    TI__Expert 8420 points
    Hi Shareef,

    What is your target application product , do you must have need this feature (reverse voltage protection )?
    The datasheet haven't the load resistor at input , since this is an old product the reverse voltage protection is specific for special case (Vin cap is big and reverse charging time is long than 4mS) . In general application this feature is not optimize .
  • 0 in reply to Michael Tan
    Prodigy 80 points
    We're using it as a USB power switch and want to protect from an end user doing something stupid. So a specific feature that is advertised to work on your products doesn't. How many more products do you sell where this is the case? Can I get a list of all power switches and regulators where the data sheet is out of date or doesn't describe additional circuitry needed to enable features advertised as standard. Thanks.
  • 0 in reply to Shareef Jalloq7
    Prodigy 80 points
    Additionally, I'm not sure your suggestion of a parallel resistor is valid. The use case is that the input voltage is at 5V and a higher voltage is applied to the output. How is the resistor going to discharge the cap in this case?
  • 0 in reply to Shareef Jalloq7
    Prodigy 80 points

    So is there an official solution to this issue?  Would a TVS diode on the input be suitable rather than a resistor?

    You also mentioned that this is an old part, is there an equivalent newer version that actually has reverse voltage protection that works?

  • 0 in reply to Shareef Jalloq7
    TI__Expert 8420 points
    Hi Shareef,

    Add the resistor is not the official solution(just let you to test the reversion voltage protection feature). After we study the actually application we have remove this feature for the newer version. The point is during reverse voltage situation the vin cap will charge up (equal to Vout )within 1~10uS , it is hard to handle this uS level in the device internal circuit , so we remove this feaure in the new part (tps25221). Generally, for the power switch there is not special requirement for this reverse voltage requirement . We have do some trade off for this feature in the tps25221.