SLVAFR8 January   2025 TPS1685 , TPS1689 , TPS25984 , TPS25984B , TPS25985 , TPS25990

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Over-Current Response of Conventional eFuse Devices
  6. 3Challenges with Current Limit Functionality
  7. 4Proposed Design Using TI's High-Current eFuses
    1. 4.1 Steady-State Over-Current Protection in TPS25984, TPS25985, TPS25990, and TPS1685 eFuses
    2. 4.2 Design Guideline
  8. 5Thermal Performance with Continual Transient Load Current
  9. 6System Level Advantages with TI's eFuse Design
    1. 6.1 Lower Number of eFuses to be Connected in Parallel
    2. 6.2 Reduced PSU Size
  10. 7Summary
  11. 8References

4.2 Design Guideline

  1. Decide the following parameters,
    1. Thermal design current (TDC) or continuous maximum steady-state current,
    2. Maximum amplitude (IMAX) of the transient peak pulse current,
    3. Maximum duration of the transient peak pulse current,
  2. Set the scalable fast-trip threshold (ISFT) at around 1.2 times IMAX to allow the transient load current to flow,
  3. The over-current threshold (IOCP) is a fraction of ISFT as depicted in Equation 6.
    Equation 6. I O C P = k × I S F T
    By default, the value of k is 0.5 in TPS25984, TPS25985, TPS25990, and TPS1685 eFuses. However, it is user-programmable in TPS25990 and TPS1685 eFuses through PMBus and pin strapping respectively. Afterword, the value of RIMON resistance is obtained using Equation 4 and considering the actual value of k.
  4. The fault timer duration needs to be set at more than the maximum duration of the transient load current pulse whose amplitude is greater than IOCP. The maximum possible fault timer duration is around 30ms. The fault timer duration is PMBus programmable in TPS25990 and hardware programmable in the other three eFuses by placing a ceramic capacitor on the ITIMER pin. The value of the capacitor is obtained using Equation 5.
  5. The number of eFuses in parallel needs to be calculated based on the RMS current rating of the device and the RMS value of the total system current or the TDC rating.