XCL225 datasheet(11/27 Pages) TOREX

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XCL225/XCL226

Series

ILX

VOUT

VLX

ILIMH=1.1A(TYP.)

ILIML=0.7A(Designed value)

1.0ms(TYP.)

VEN/SS

■

OPERATIONAL EXPLANATION (Continued)

The reference voltage source provides the reference voltage to ensure stable output voltage of the DC/DC converter.

The ramp wave circuit determines switching frequency. The frequency is fixed internally 1.2MHz.

Clock pulses generated in this circuit are used to produce ramp waveforms needed for PWM operation.

The error amplifier is designed to monitor output voltage. The amplifier compares the reference voltage with the feedback

voltage divided by the internal voltage divider, RFB1 and RFB2. When a voltage is lower than the reference voltage, then the

voltage is fed back, the output voltage of the error amplifier increases. The error amplifier output is fixed internally to deliver an

optimized signal to the mixer.

The current limiting circuit of the XCL225/XCL226 series monitors the current that flows through the High-side driver transistor

and Low-side driver transistor, and when over-current is detected, the current limiting function activates.

①

Low-side driver Tr. 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

Tr. 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 Tr. current limit value ILIML. Control to lower the switching frequency fOSC is also

performed. When the over-current state is released, normal operation resumes.

②

High-side driver Tr. 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

Tr. 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 ILIMH. ILIML < ILIMH is set inside the IC, and therefore the Low-side driver Tr. 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 Tr. when state ① or ② continues for 1.0ms (TYP.). The Lx pin 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/SS 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 Tr. current limit value ILIML=0.7A (Designed value)

High-side driver Tr. current limit value ILIMH=1.1A (TYP.)

< Current limiting timing chart >

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