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 ILIMIT1 is determined
by RLIMIT according to equation 6. The 2nd threshold
ILIMIT2 equals to 1.6 times of ILIMIT1.
- Case 1: If the load
current IBUS is in the range ILIMIT2 >
IBUS > ILIMIT1, and the duration <
tOC_HIC_DEG, the external MOSFET will remain on and
VBUS will stay unchanged, as shown in Figure 10-18.
- Case 2: If the load
current IBUS is in the range ILIMIT2 >
IBUS > ILIMIT1 and the duration >
tOC_HIC_DEG, the external MOSFET will current limit
to ILIMIT1, 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 ILIMIT1 and
continues > tOC_HIC_RST, the external MOSFET will
resume always on.
- Case 3: If the load
current IBUS > ILIMIT2, the external MOSFET
will current limit to ILIMIT1 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 IBUS < ILIMIT1
for tOC_HIC_RST, the external MOSFET will resume always
on.
- Buck average current limit
- When TPS2583xA-Q1
uses Buck average current limit, it has only one current limit
threshold determined by RLIMIT according to Equation 6.
- In order to meet the
MFI OC requirement, an RC network is needed in parallel with
Rlimit resistor as shown in Figure 10-21. Suggest selecting Rpara = Rlimit,
Cpara = 100 nF.