11/17

XC9254R

Series

■NOTE ON USE

1. The XC9254R 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.

possibility that some cycles may be skipped completely.

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:

L: Coil Inductance Value

7. When the peak current which exceeds limit current flows within the specified time, the built-in Pch MOS 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. 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.

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

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 Nch MOS driver transistor is ON, there is almost no potential difference at both ends of the coil since the

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 Pch MOS driver transistor.

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.

LX

ILX

ILIM

Limit >

# mS

①

②

③

④

⑤

Delay

ms