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TPS2H000-Q1: Current limit accuracy

Kenji Ohno1
Genius 5095 points
Part Number: TPS2H000-Q1

Hi Team,

I found the accuracy of the current limit range of TPS2H000 from the applicationnote(slva859b).

My customer used an external resistance of 560Ω and set the current limit value to 428mA, but the current limit was applied at 520mA.

It exceeds ±15% accuracy.

I understand that the current limit is 428mA when the external resistance is 560Ω. Is this correct?

I would like to know why 520mA has a current limit.

Best Regards,

Kenji

  • 0
    TI__Genius 13300 points

    Hello Ohno-san,

    Assuming a 1% tolerance on the resistor value chosen, the worst case minimum current limit would be 360.6 mA, and the worst case maximum current limit would be 497.9 mA. Something else to consider is a soft short event- when the current slowly approaches the set limit. When the VDS voltage is less than 2.5V the current limit can trip up to 1.5x the set current limit. When the VDS voltage is greater than 2.5V it is considered a hard short and the 1.5x does not apply.
    Also, if a current limit of 428 mA is the goal, you'll have to consider the +/-15% for the Kcl value as well. The min Kcl value used to calculate the resistor value would be 255 and the max 345. That would translate to a range of resistor values from 476 Ohm(round down to standard 475 Ohm resistor with 1% tolerance) and 645 Ohm (round down to standard 634 Ohm with 1% tolerance). Resistor tolerances will affect the calculations.

    Regards,

    Kalin Burnside

  • 0 in reply to Kalin Burnside
    Genius 5095 points

    Hi Kalin-san,

    Thank you for your answer.

    VDS voltage is more than 2.5V. (VIN;5V , Vs; 24V)

    I understand that resistance tolerances do matter.

    My customer actually measured the resistance used. Resistance value ;558Ω/548Ω/560Ω/569Ω

    My customers checked the current limit values, but all of them were unexpected current limits.

     0.8×300/558=430mA (setting limit) with a resistance value of 558Ω (±15%; 365-494mA)         Result: 520mA

    0.8×300/548=437mA (setting limit) with a resistance value of 548Ω (±15%; 372 to 503mA)       Result: 530mA

    0.8 x 300/560 = 428mA (resistance limit 560Ω) (±15%; 364 to 492mA)                                       Result: 520mA

    0.8×300/569 = 421mA (setting limit) with resistance 569Ω (±15%; 358-485mA)                          Result: 510mA

    I don't understand the reason why the current limit value is larger than the set current limit value.

    The larger the resistance value used, the lower the limit current, but it is necessary to understand why the limit current becomes larger than expected.

    Thank you for  your great support!

    Kenji

  • 0 in reply to Kenji Ohno1
    TI__Genius 13300 points

    Hello Ohno-san,

    Could you give me more information on how your customer is attempting to hit the current limit? (I.e are they shorting the device to ground, slowly ramping down the resistance in the load, etc)

    Also, if you could provide a schematic of the HSS and scope readings it could help resolve the issue.

    Regards,

    Kalin Burnside