XCL201 Datasheet, PDF (8/21 Pages) Torex Semiconductor – Inductor Built-in Step-Down “micro DC/DC” Converters

XCL201/XCL202 Series
■OPERATIONAL DESCRIPTION (Continued)
<Current Limit>
The current limiter circuit of the XCL201/XCL202 series monitors the current flowing through the P-channel MOS driver transistor connected to
the Lx pin, and features a combination of the current limit mode and the operation suspension mode.
①çWhen 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.
②çWhen the driver transistor is turned off, the limiter circuit is then released from the current limit detection state.
③çAt the next pulse, the driver transistor is turned on. However, the transistor is immediately turned off in the case of an over current state.
④çWhen the over current state is eliminated, the IC resumes its normal operation.
The IC waits for the over current state to end by repeating the steps ①çthrough ③. If an over current state continues for a few milliseconds and
the above three steps are repeatedly performed, the IC performs the function of latching the OFF state of the driver transistor, and goes into
operation suspension state. Once the IC is in suspension state, operations can be resumed by either turning the IC off via the CE pin, or by
restoring power to the V_IN pin. The suspension state does not mean a complete shutdown, but a state in which pulse output is suspended;
therefore, the internal circuitry remains in operation. The current limit of the XCL201/XCL202 series can be set at 800mA at typical.
Depending on the state of the PC Board, latch time may become longer and latch operation may not work. In order to avoid the effect of noise,
an input capacitor is placed as close to the IC as possible.
Limit < # ms
Limit > # ms
Current Limit LEVEL
I_Lx
0mA
V_OUT
Vss
L_x
V_CE
Restart
V_IN
ç
<Short-Circuit Protection>
The short-circuit protection circuit monitors the internal R1 and R2 divider voltage from the V_OUT pin (refer to FB point in the block diagram
shown in the previous page). In case where output is accidentally shorted to the Ground and when the FB point voltage decreases less
than half of the reference voltage (Vref) and a current more than the I_LIM flows to the driver transistor, the short-circuit protection quickly
operates to turn off and to latch the driver transistor. In the latch state, the operation can be resumed by either turning the IC off and on via
the CE pin, or by restoring power supply to the V_IN pin.
When sharp load transient happens, a voltage drop at the V_OUT is propagated to the FB point through C_FB, as a result, short circuit protection
may operate in the voltage higher than 1/2 V_OUT voltage.
<UVLO Circuit>
When the V_IN pin voltage becomes 1.4V or lower, the P-channel output driver transistor is forced OFF to prevent false pulse output caused by
unstable operation of the internal circuitry. When the V_IN pin voltage becomes 1.8V or higher, switching operation takes place. By releasing
the UVLO function, the IC performs the soft start function to initiate output startup operation. The soft start function operates even when the VIN
pin voltage falls momentarily below the UVLO operating voltage. The UVLO circuit does not cause a complete shutdown of the IC, but causes
pulse output to be suspended; therefore, the internal circuitry remains in operation.
8/21