RP505K Series 1A Step-down DC/DC Converters with Synchronous Rectifier No.EA-273-210909 OUTLINE *1 The RP505K Series are low supply current CMOS-based 1A step-down DC/DC Converters with synchronous rectifier. Each of these ICs consists of an oscillator, a reference voltage unit, an error amplifier, a switching control circuit, a mode control circuit, a soft-start circuit, a latch type protection circuit, an under voltage lock out (UVLO) circuit, a thermal shutdown circuit, and a switching transistors. A low ripple, high efficiency synchronous rectifier step-down DC/DC converter can be easily composed of this IC with only an inductor and capacitors. Since the package is DFN(PLP)2020-8, high density mounting on boards is possible. In the RP505K series, as for the A version and B version, since feedback resistors are built-in, the voltage is fixed internally. 0.1V step output can be set by laser-trim and 1.5%(VOUT1.2V) or 18mV(VOUT<1.2V) tolerance is guaranteed. As for the C version, output voltage is adjustable with external divider resisters. By inputting a signal to MODE pin, the RP505K Series can choose PWM/VFM alternative mode or forced PWM mode. In low output current, PWM/VFM alternative mode automatically switches from PWM to VFM in order to achieve high efficiency. Likewise, in low output current, Forced PWM mode switches at fixed frequency in order to reduce noise. As protection circuits, the RP505K Series contain a current limit circuit which limits the Lx peak current in each clock cycle, and a latch type protection circuit which latches the built-in driver to the OFF state if the load current exceeds the limit value or the output short continues for a specified time (the protection delay time). The latch protective circuit can be released by once putting the IC into the standby mode with the CE pin and then into the active mode, or, by turning the power off and back on. Setting the supply voltage lower than the UVLO detector threshold can also release the latch protective circuit. The RP505K Series also contain a thermal shutdown circuit which detects the overheating and resets the IC when the junction temperature of the RP505K Series exceeds the specified temperature. *1 This is an approximate value, because output current depends on conditions and external parts. FEATURES Supply Current ...................................................... Typ. 40A (VFM mode with no-load) Standby Current .................................................... Max. 5A Input Voltage Range ............................................. 2.3V to 5.5V (Absolute maximum rating: 6.5V) Output Voltage Range (Ver.A,B) ........................... 0.6V to 3.3V (Adjustable in 0.1V steps. Note: As for 0.8V or less, input voltage range is limited.) (Ver.C) .............................. 0.8V to 3.3V Output Voltage Accuracy (Ver.A,B) ....................... 1.5% (VOUT1.2V), 18mV (VOUT<1.2V) Feedback Voltage Accuracy (Ver.C) ..................... 9mV (VFB=0.6V) Temperature-Drift Coefficient of Output Voltage/ Feedback .............................................................................. Typ. 100ppm/C Oscillator Frequency ............................................. Typ. 2.25MHz Oscillator Maximum Duty Cycle ............................ Min. 100% Built-in Driver ON Resistance ............................... Typ. Pch. 0.23, Nch. 0.20 (VIN=3.6V) UVLO Detector Threshold ..................................... Typ. 2.0V Soft-start Time ....................................................... Typ. 0.15ms LX Current Limit Circuit .......................................... Typ. 1.7A Latch Type Protection Circuit ................................ Typ. 1.5ms Package ................................................................ DFN(PLP)2020-8 1 RP505K APPLICATIONS Power source for portable equipment such as cellular, PDA, DSC, Notebook PC Power source for HDD, WLAN. Power source for Li-ion battery-used equipment BLOCK DIAGRAMS RP505Kxx1A PVIN Ramp Current Compensation Feedback Thermal AVIN UVLO Current Protection Detector LX Switching Vref Soft Start Control Mode PGND MODE OSC Control Chip CE Enable VOUT AGND 2