23/49

XCM519

Series

■NOTE ON USE (Continued)

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.

Care must be taken when laying out the PC Board, in order to prevent misoperation of the current limit mode. 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.

9.

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

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

11. 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.

12. 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 DCOUT 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 DCOUT 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.

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.

14. High step-down ratio and very light load may lead an intermittent oscillation.

15. During PWM / PFM automatic switching mode, operating may become unstable at transition to continuous mode.

Please verify with actual parts.

LX

ILX

ILIM

Limit >

# mS

①

②

③

④

⑤

Delay

ms

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