R1234D Datasheet, PDF (11/26 Pages) RICOH electronics devices division – PWM/VFM Step-Down DC/DC CONVERTER with Synchronous Rectifier

R1234D
When you use these ICs, consider the following issues;
• Input same voltage into the power supply pins, VIN and VDD. Set the same level as AGND and PGND.
• When you control the CE pin and MODE pin by another power supply, do not make its "H" level more than
the voltage level of VIN/VDD pin.
• Set external components such as an inductor, CIN, COUT as close as possible to the IC, in particular,
minimize the wiring to VIN pin and PGND pin.
• At stand by mode, (CE="L"), the LX output is Hi-Z, or both P-channel transistor and N-channel transistor of
LX pin turn off.
• Use an external capacitor COUT with a capacity of 10µF or more, and with good high frequency
characteristics such as tantalum capacitors.
• At VFM mode, (MODE="H"), Latch protection circuit does not operate.
• If the mode is switched over into PWM mode from VFM mode during the operation, change the mode at
light load current. If the load current us large, output voltage may decline.
• Reinforce the VIN, PGND, and VOUT lines sufficiently. Large switching current may flow in these lines. If the
impedance of VIN and PGND lines is too large, the internal voltage level in this IC may shift caused by the
switching current, and the operation might be unstable.
The performance of power source circuits using these ICs extremely depends upon the peripheral circuits.
Pay attention in the selection of the peripheral circuits. In particular, design the peripheral circuits in a way that
the values such as voltage, current, and power of each component, PCB patterns and the IC do not exceed their
respected rated values.
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