XC9206 / 9207/ 9208 Series

PWM, PWM/PFM Switchable Step-Down DC/DC Converters with Driver Transistor Built-In

# Application Information (Continued)

Ipk = (VIN - VOUT) x On Duty / (2 x L x FOSC) + IOUT

OnDuty

: OnDuty ratio of Pch Driver Transistor

L

: Coil Inductance Value

FOSC

: Oscillation Frequency

$ The increase of ripple voltage (1.2MHz)

L

: 4.7µH

CDRH3D16 SUMIDA

SD

: CRS02

TOSHIBA

CIN

: 4.7µF

Ceramic

CL

: 10µF

Ceramic

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

5. 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 operating, 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:

6. When the peak current which exceeds limit current flows within the specified time, the built-in Pch driver transistor is turned 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 coil or the schottky diode.

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.

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

capacitors are placed as close to the chip as possible.

Semiconductor Ltd.

CH1:Lx

CH2:VOUT

AC-COUPLED

CH1:Lx

CH2:VOUT

AC-COUPLED

CH1:Lx

CH2:VOUT

AC-COUPLED

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

When the series' duty cycle is digitally signalized, the linear duty cycle and the digitally signalized duty cycle cannot carry out completely the same

change, which means that the duty cycle does not change linearly. The output is stabilized by applying the phase compensation and adjusting the

duty cycle, even when the duty cycle loses the linear change in the whole circuit.

When the state where the output was stabilized is continued by applying phase compensation to duty cycle which lost linearity, ripple voltage does

not increase more than it.

The ripple voltage may increase to about several 10mV according to operating conditions. It is possible, by increasing the capacitance values, to

reduce the ripple voltage. The operating conditions are greatly influenced by the dropout voltage, the load current, the delay-time, or the external

components, such as the coil inductance, and the capacitance values. Verification with actual parts should be done.

Data Sheet

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