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XCL223/XCL224

Series

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OPERATIONAL EXPLANATION (Continued)

<Current Limit>

The current limiter circuit of the XCL223/XCL224 series monitors the current flowing through the P-channel MOS driver

transistor connected to the Lx pin. When the driver current is greater than a specific level, the current limit function operates to

turn off the pulses from the Lx pin at any given timing. When the over current state is eliminated, the IC resumes its normal

operation.

<Reference voltage source, soft-start function>

The reference voltage forms a reference that is used to stabilize the output voltage of the IC. After chip enable of the IC, the

reference voltage connected to the error amp increases linearly during the soft-start interval.

This allows the voltage divided by the internal R1 and R2 resistors and the reference voltage to be controlled in a balanced

manner, and the output voltage rises in proportion to the rise in the reference voltage. This operation prevents rush input current

and enables the output voltage to rise smoothly.

If the output voltage does not reach the set output voltage within the soft start time, such as when the load is heavy or a large

capacity output capacitor is connected, the balancing of the voltage divided by the internal resistors R1 and R2 and the

reference voltage is lost, however, the current restriction function activates to prevent an excessive increase of input current,

enabling a smooth rise of the output voltage.

<PWM/PFM selection circuit>

is determined by the input voltage and output voltage regardless of the load.

PWM/PFM auto switching control is a discontinuous conduction mode at light loads, and lowers the switching frequency to

reduce switching loss and improve efficiency.

The XCL223 series is internally fixed to PWM control.

The XCL224 series is internally fixed to PWM/PFM auto switching control.

<CE function>

Operation starts when “H” voltage is input into the CE pin. The IC can be put in the shutdown state by inputting “L” voltage into

the CE pin. In the shutdown state, the supply current of the IC is 0μA (TYP.), and the Pch MOS driver Tr. and Nch MOS switch

Tr. for synchronous rectification turn off. The CE pin is a CMOS input and the sink current is 0μA.

<UVLO>

(TYP.) or higher, switching operation takes place. By releasing the UVLO function, the IC performs the soft start function to

initiate output startup operation. The UVLO circuit does not cause a complete shutdown of the IC, but causes pulse output to be

<Thermal Shutdown>

For protection against heat damage of the ICs, thermal shutdown function monitors chip temperature. The thermal shutdown

circuit starts operating and the P-ch MOS driver and N-ch MOS driver transistor will be turned off when the chip’s temperature

reaches 150℃. When the temperature drops to 120℃ (TYP.) or less after shutting of the current flow, the IC performs the soft-

start function to initiate output startup operation.

<Short-circuit protection function>

The short-circuit protection circuit protects the device that is connected to this product and to the input/output in

situations such as when the output is accidentally shorted to GND. The short-circuit protection circuit monitors the output

voltage, and when the output voltage falls below the short-circuit protection threshold voltage, it turns off the Pch MOS driver Tr

and latches it. Once in the latched state, operation is resumed by turning off the IC from the CE pin and then restarting, or by re-