XC9248 Series
■OPERATIONAL EXPLANATION (Continued)
<Current limiting>
The current limiting circuit of the XC9248 series monitors the current that flows through the Low side and High side Nch MOS
driver Tr, and when over-current is detected, the current limiting function activates.
①
Low side driver current limiting
The current in the Low side driver Tr. is detected to equivalently monitor the bottom value of the coil current.
The Low side driver current limiting function prohibits the High side driver Tr. from turning on in an over-current state where the
bottom value of the coil current is higher than the Low side driver current limit value ILIMLS
.
Control to lower the switching frequency fOSC is also performed. When the over-current state is released, normal operation
resumes.
②
High side driver current limiting + Low side driver current limiting
The current in the High side driver Tr. is detected to equivalently monitor the peak value of the coil current.
The High side driver current limiting function forcibly turns off the High side driver Tr. when the peak value of the coil current
reaches the High side driver current limit value ILIMHS. ILIMLS < ILIMHS is set inside the IC, and therefore the Low side driver current
limiting function of ① above also detects the over-current state at this time. When the over-current state is released, normal
operation resumes.
③
Over-current latch (Type A)
Type A turns off the High side and Low side driver transistors when state ① or ② continues for 1.1 ms (TYP.). The LX pin is in
the CL discharged state, and is latch-stopped at the GND level (0V).
The latch-stopped state only stops the pulse output from the Lx pin; the internal circuitry of the IC continues to operate.
To restart after latch-stopping, L level and then H level must be input into the EN pin, or VIN pin re-input must be performed
(after lowering the voltage below the UVLO detection voltage) to resume operation by soft start.
The over-current latch function may occasionally be released from the current limit detection state by the effects of ambient
noise, and it may also happen that the latch time becomes longer or latching does not take place due to board conditions. For
this reason, place the input capacitor as close as possible to the IC.
Type B is an automatic recovery type that performs the operation of ① or ② until the over-current state is released.
Low side driver current limit value ILIMLS=2.1A (MIN.)
High side driver current limit value ILIMHS=4.1A (TYP.)
10/21
TOREX [ Torex Semiconductor ]
