• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 284 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

TPS7H2201-SP: 22A fast trip capability

TPS7H2201-SP: Programmable Current Limit and Internal Trip Timer

Joshua Escobar
Prodigy 100 points
Part Number: TPS7H2201-SP

This question is primarily in reference to this previous post.

The datasheet and the post linked above suggest that when the internal timer is used (i.e. when Pin 11 is connected to VIN) that the programmable current limit is essentially ignored - that only the fast trip limit of 22A will be effective. Is my understanding of this correct?

If we want to have a very fast trip timer, but for a programmed limit < 22A, what is the fastest time that can be reliably be used? In other words, what is the smallest capacitor that can be connected to the ILTIMER pin to have reliable overcurrent protection?

  • 0
    TI__Expert 7145 points

    Hi Joshua,

    When the internal timer pin (ILTIMER) is connected to VIN, the programmable current limit is not ignored. In this configuration the device will limit the current to the value set by the resistor on the IL pin. However, when using the internal timer, the programable current limit accuracy specified in the electrical characteristics table may be worse. I will talk with the designer to clarify this detail and follow up with further guidance on how much time is required to ensure the programable current limit performs reliably. 

    Figure 27 from the datasheet (below) shows an example of this behavior where retry mode has also been disabled by grounding the RTIMER pin. 

     

    Connecting ILTIMER to VIN so that the device uses the internal timer is the best option for achieving the shortest amount of time spent in current limiting mode. As stated in the electrical characteristics table, this time is typically 15 us and can be up to 35 us.

    Thanks,

    Sarah

  • 0 in reply to Sarah Koch
    Prodigy 100 points

    Thank you for the additional information. I would definitely welcome further clarification regarding the accuracy of the internal timer and it's ability to catch overcurrent events based on the programmable current limit.

    We would like overcurrent events to be stopped as quickly as possible. To that end, using the internal timer makes the most sense. But we cannot allow a 22A trip current. We'd like to be able to set our trip current as low as 2.4A.

  • 0 in reply to Joshua Escobar
    TI__Expert 7145 points

    Hi Joshua,

    Thank you for the additional information about your design goals. I am currently searching to see if there is any informal data I can provide on the minimum time needed for the programable current limit to meet the accuracy spec given in the datasheet and will get back to you as soon as possible.

    Thanks,

    Sarah

  • 0
    TI__Expert 7145 points

    Hi Joshua,

    Thank you for your patience while I gathered more information. After discussing it with the designer, the minimum current limit timer we recommend to ensure the programable current limit meets the datasheet accuracy spec is 100us.

      .

    Just to make sure we’re on the same page, using the ILTIMER pin to set the timer to 100us or more allows the device to remain in current limiting mode long enough for the current through the device to settle within the accuracy range of the programmed current limit, but it would not prevent fast trip mode if the overcurrent event was large (such as a short).

      .

    While the 22-A peak fast trip current is large, this value is due to the amount of time it takes for the internal circuitry to detect and respond to a large overcurrent event. Many other devices would also allow current spikes due to internal circuitry delays, but they do not usually address or define these scenarios. The TPS7H2201-SP, on the other hand, is able to provide some definition for what a short might look like and how long it might last before being stopped.

      .

    If more information is known about the overcurrent event, the peak current can be calculated using the equations below:

        .

    Since you are wanting the device to shut off as quickly as possible, using the internal timer would likely be the best option. Let me know if you have any further questions or if there is anything I can clarify.

      

    Thanks,

    Sarah