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

5 Thermal Performance with Continual Transient Load Current

In the presence of transient load current, the device junction temperature rise is proportional to the square of the root mean square (RMS) current flowing through it instead of the average DC current. The junction temperature is obtained using Equation 7.

Equation 7. TJ=TA+IRMS2×RDSon×RθJA

TJ: Device junction temperature,

TA: Device ambient temperature,

IRMS: RMS value of the current flowing through a single device,

RDSon: ON resistance of each eFuse,

RθJA: Junction-to-ambient thermal resistance of the eFuse.

Under the presence of transient load scenarios, the device junction temperature must be limited to the maximum recommended operating temperature of 125°C at the elevated system ambient temperature. To make sure of this, either the value of RθJA must be lowered by improving the thermal management and PCB layout or the number of devices in parallel must be increased to the next integer. To avoid the effect of electromigration over the lifetime of the device to maintain long-term reliability, the transient peak current flowing through each device needs to be close to the peak current rating (for example, TPS25985 is for 60A RMS current and 80A peak current). The thermal performance of TPS25985 eFuse with the transient load of 50A for (100-X) ms and 80A for X ms is shown in Figure 5-1, where X is the PEAK Current Applied Duration in ms.

Thermal Performance of TPS25985 eFuse under Transient LoadFigure 5-1 Thermal Performance of TPS25985 eFuse under Transient Load