XCL208/XCL209
Series
■NOTE ON USE
1. For temporary, transitional voltage drop or voltage rising phenomenon, the IC is liable to malfunction should the ratings be
exceeded.
2. The XCL208/XCL209 series is designed for use with ceramic output capacitors. If, however, the potential difference is too
large between the input voltage and the output voltage, a ceramic capacitor may fail to absorb the resulting high switching
energy and oscillation could occur on the output. In this case, increase 10μF to the output capacitance for adding
insufficient capacitance. Also, if the output capacitance is too large, the output voltage is slowly rising and the IC may not
operate. Adjust the output capacitance so that the output voltage can go up within the soft-start time.
3. Spike noise and ripple voltage arise in a switching regulator as with a DC/DC converter. These are greatly influenced by
external component selection, such as the coil inductance, capacitance values, and board layout of external components.
Once the design has been completed, verification with actual components should be done.
4. Depending on the input-output voltage differential, or load current, some pulses may be skipped as 1/2, 1/3 and the ripple voltage
may increase.
5. When the difference between input and output is large in PWM control, very narrow pulses will be outputted, and there is the
possibility that 0% duty cycles may be continued during some cycles.
6. When the difference between input and output is small, and the load current is heavy, very wide pulses will be outputted and
there is the possibility that 100% duty cycles may be continued during some cycles.
7. With the IC, the peak current of the coil is controlled by the current limit circuit. Since the peak current of the coil increases
when dropout voltage or load current is high, current limit starts operation, and this can lead to instability. When peak current
becomes high, please adjust the coil inductance value and fully check the circuit operation. In addition, please calculate the
peak current according to the following formula:
Ipk = (VIN - VOUT) x OnDuty / (2 x L x fOSC) + IOUT
L: Coil Inductance Value
fOSC: Oscillation Frequency
8. When the peak current which exceeds limit current flows within the specified time, the built-in P-ch driver transistor turns off.
During the time until it detects limit current and before the built-in transistor can be turned off, the current for limit current
flows; therefore, care must be taken when selecting the rating for the external components such as a coil.
9. When VIN is less than 2.4V, limit current may not be reached because voltage falls caused by ON resistance.
10. 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, the board should be laid out so that input capacitors are placed as close to the IC as possible.
11. Use of the IC at voltages below the minimum operating voltage range may lead to instability.
12. This IC should be used within the stated absolute maximum ratings of external components in order to prevent damage to
the device.
13. When the IC is used in high temperature, output voltage may increase up to input voltage level at no load because of the
leak current of the driver transistor.
14. The current limit is set to 1000mA (MAX.) at typical. However, the current of 1000mA or more may flow.
In case that the current limit functions while the VOUT pin is shorted to the GND pin, when P-ch MOSFET is ON, the potential
difference for input voltage will occur at both ends of a coil. For this, the time rate of coil current becomes large. By
contrast, when N-ch MOSFET is ON, there is almost no potential difference at both ends of the coil since the VOUT pin is
shorted to the GND pin. Consequently, the time rate of coil current becomes quite small. According to the repetition of this
operation, and the delay time of the circuit, coil current will be converged on a certain current value, exceeding the amount of
current, which is supposed to be limited originally. Even in this case, however, after the over current state continues for
several ms, the circuit will be latched. A coil should be used within the stated absolute maximum rating in order to prevent
damage to the device.
①Current flows into P-ch MOSFET to reach the current limit (ILIM).
②The current of ILIM or more flows since the delay time of the circuit occurs during from the detection of the current limit to OFF of P-ch MOSFET.
③Because of no potential difference at both ends of the coil, the time rate of coil current becomes quite small.
④Lx oscillates very narrow pulses by the current limit for several ms.
⑤The circuit is latched, stopping its operation.
②
①
③
④
⑤
Limit ＞#ms
Delay
Lx
ILIM
ILx
13/22
TOREX [ Torex Semiconductor ]
