Apple has defined new overcurrent protection requirements in its latest MFI spec. TPS2583xA-Q1 also implements a novel current limit inside to meet the MFI OC requirement.

The settings are described below:

• With external MOSFET: When TPS2583xA-Q1 uses an external FET for current limit, it actually has two current limit threshold. The 1st threshold I_LIMIT1 is determined by R_LIMIT according to equation 6. The 2nd threshold I_LIMIT2 equals to 1.6 times of I_LIMIT1.
  • Case 1: If the load current I_BUS is in the range I_LIMIT2 > I_BUS > I_LIMIT1, and the duration < t_{OC_HIC_DEG}, the external MOSFET will remain on and V_BUS will stay unchanged, as shown in Figure 10-18.
    Figure 10-18 Two level Current Limit Methodology with ext MOSFET Case 1
  • Case 2: If the load current I_BUS is in the range I_LIMIT2 > I_BUS > I_LIMIT1 and the duration > t_{OC_HIC_DEG}, the external MOSFET will current limit to I_LIMIT1, then enter hiccup mode with 2 ms of on-time and 263 ms of off-time, as shown in Figure 10-19. When the load current decreases below I_LIMIT1 and continues > t_{OC_HIC_RST}, the external MOSFET will resume always on.
    Figure 10-19 Two Level Current Limit Methodology with ext MOSFET Case 2
  • Case 3: If the load current I_BUS > I_LIMIT2, the external MOSFET will current limit to I_LIMIT1 immediately, then enter hiccup mode with 2 ms of on-time and 263 ms of off-time, as shown in Figure 10-20. When the load current I_BUS < I_LIMIT1 for t_{OC_HIC_RST}, the external MOSFET will resume always on.
    Figure 10-20 Two Level Current Limit Methodology with ext MOSFET Case 3
• Buck average current limit
  • When TPS2583xA-Q1 uses Buck average current limit, it has only one current limit threshold determined by R_LIMIT according to Equation 6.
  • In order to meet the MFI OC requirement, an RC network is needed in parallel with R_limit resistor as shown in Figure 10-21. Suggest selecting R_para = R_limit, C_para = 100 nF.
  Figure 10-21 RC Network in Parallel with R_limit