R1240K003A-TR Ver la hoja de datos (PDF) - RICOH Co.,Ltd.
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R1240K003A-TR Datasheet PDF : 19 Pages
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R1240x
NO.EA-190-170609
TECHNICAL NOTES
The performance of a power source circuit using this device is highly dependent on a peripheral circuit. A
peripheral component or the device mounted on PCB should not exceed its voltage, current or power ratings.
When designing a peripheral circuit, please be fully aware of the following points. (Refer to our PCB layout for
detailed information).
• External components must be connected as close as possible to the ICs and make wiring as short as
possible. Especially, the capacitor connected in between VIN and GND pin must be wiring the shortest.
The operating may be unstable due to the change of the electric potential of internal ICs by the switching
current when the impedance of the power supply line and GND line is high. Make the power supply and
GND lines sufficient. It is also necessary to give careful consideration to design the wiring of the power
supply, GND, Lx, VOUT and the inductor because of the large current by the function of switching is
flowing into them. Besides, the wiring between the resistance (R1), which set the output voltage, and the
wiring of the inductor must separate from the load wiring.
• The ceramic capacitors have low ESR (Equivalent Series Resistance) type are recommended for the
ICs. The recommendation of CIN capacitor between VIN and GND is more than 10 µF, and COUT
capacitor is more than 10 µF in the case VOUT ≥ 1.8 V or more than 20 µF in the case 1.8 V > VOUT.
Please check the bias dependence and the temperature variations of the ceramic capacitors.
• Normally, please select the inductor value in the range between 4.7 µH and 10µH in the case of VOUT ≥
5 V, 4.7 µH in the case of 5 V > VOUT ≥ 1.8 V and 2.2 µH in the case of 1.8 V > VOUT. The internal phase
compensation of this IC is designed with the above-mentioned inductor value and COUT ceramic
capacitor value. When the inductor value is small, there is a possibility to trigger the over-current
protection circuit by the peak switching current. As the peak switching current might reach to the limited
value when the load current increase a lot.
• Please note; the over-current protection circuit is influenced by the temperature shift caused by
operation of the IC.
• For the diode, please use the Schottky diode, which parasitic capacitance is small as possible, as, there
is a possibility that the operating of IC becomes unstable by the large switching current.
• Output voltage is set by VOUT = VFB × (R1 + R2) / R2. If the values of R1 and R2 are large, the impedance
of VFB pin increases, and pickup the noise may result. The recommendation value range of R2 is
approximately between 1.2 kΩ to 16 kΩ. If the operation may be unstable, reduce the impedance of VFB
pin.
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