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XCL205/XCL206/XCL207 Series

■NOTE ON USE

④

Limit > # ms

⑤

③

②

①

Delay

Lx

ILIM

ILx

1. The XCL205/XCL206/XCL207 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. If the input-output potential difference is large,

connect an electrolytic capacitor in parallel to compensate for insufficient capacitance.

2. 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.

3. Depending on the input-output voltage differential, or load current, some pulses may be skipped, and the ripple voltage

may increase.

4. When the difference between VIN and VOUT is large in PWM control, very narrow pulses will be outputted, and there is the

possibility that some cycles may be skipped completely.

5. When the difference between VIN and VOUT is small, and the load current is heavy, very wide pulses will be outputted and

there is the possibility that some cycles may be skipped completely.

6. With the IC, the peak current of the coil is controlled by the current limit circuit.

Since the peak current 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

7. 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.

8. When VIN is less than 2.4V, limit current may not be reached because voltage falls caused by ON resistance.

9. 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.

10. Use of the IC at voltages below the recommended voltage range may lead to instability.

11. This IC should be used within the stated absolute maximum ratings in order to prevent damage to the device.

12. 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.

13. The current limit is set to 1350mA (MAX.) at typical. However, the current of 1350mA 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.