Ricoh R1243 Series, 30V
2A PWM Step Down DCDC Converter
The current mode controlled R1243 is a remarkable new DCDC Converter in Ricoh's semiconductor product range and has various enhanced features compared to our current products. The R1243 can operate up to 30V, whilst the adjustable output voltage can be set from 0.8V to 15V by 2 external resistors. By following the component recommendations as mentioned in the reference circuit, one can obtain maximum 2A output current from the power supply.
There are two current limit types are available for the R1243; depending on the preference, one can select from a latched or foldback current limit type. The latched type circuit is triggered when the Lx current exceeds the maximum level and when the feedback voltage decreases below the nominal voltage. When this condition remains for more than 2ms the chip is set into the off mode. In order to resume to normal operation one needs to restart the chip again. The foldback type is triggered when the feedback voltage decreases below the nominal voltage. As a result the oscillator frequency will be lowered to 1/4 of the normal frequency; it is because during a short condition the duty cycle drops below the minimum level and the current limit cannot be maintained at this level. In the foldback limit condition, the R1243 remains active and recovers automatically to normal operation as soon the cause of the short or overcurrent is removed.
Another additional protection is the UVLO (Under Voltage Lock Out) circuit, it keeps the chip disabled as long as the input voltage is below a specific minimum level, to prevent that the chip operates below the required input voltage specifications. The R1243 has two options for the operating frequency, one can select from 330kHz and 1MHz version.
A soft start function is embedded to limit high inrush currents during the start up period, the period can be set by an external Css capacitor. The R1243 is equipped with a flag output pin which has the purpose to provide a "power good" signal. When a shutdown, current limit, UVLO, softstart and over/under voltage condition occur, the flag output will change to low. The R1243 is available in HSOP-8E package only which is convenient to use on high density and small circuit boards.
Operating Voltage: Min. 4.5V to Max. 30V Output Voltage (adjustable): 0.8V to 15.0V Feedback Voltage: Typ. 0.8V Lx Peak Current Limit: Max. 2.0A Short Protection: Latched or Fold-Back Operating Frequency (fixed version): 330kHz, 1MHz Operating Mode: PWM Efficiency: (Vin=12V, Vout=3.3V, Freq = 1MHz) Max. 95%
Additional Circuits: Thermal Protection, Under Voltage Lock Out Soft Start Function (adjustable): (No Css capacitor) Typ. 0.4ms Inductor: 2.2?H - 10?H Capacitors: Cin Ceramic 10?F, Cout Ceramic 10?F - 47?F Package R1243S: (L6.2 x W5.2 x H1.5mm) HSOP-8E
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