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A p p l i c a t i o n N o t e Internal or External Output Driver Transistor Ricoh has DC/DC converter types available with an internal output transistor and external output transistor. In internal types have an Lx pin and are called DC/DC converters, the external types have an EXT pin and are called DC/DC controllers. (If a specific product has both types available it is listed as a DC/DC converter) When using an external output transistor, select a power MOSFET. When efficiency at high loads is important select a MOSFET with a low ON resistance, but when efficiency at a low loads is more important select a MOSFET with small gate capacity. Please use a MOSFET that has a maximum drain current higher than the maximum coil current (ILmax). RP505Kxx1A/B R1224Nxx2E/F/G/H/L/M (Internal output transistor type) (External output transistor type) PVIN AVIN Ramp Compensation Thermal UVLO Shutdown Current Feedback Current Detector LX VIN 5 OSC 3 VOUT MODE CE Soft Start Vref Chip Enable Mode Control Switching Control OSC PGND VOUT EXT 4 PWM/VFM CONTROL - + Protection Amp - + Vref Soft Start Chip Enable 1 CE UVLO + - Vref AGND 2 GND Products With Internal Output Transistor RN5RK R1200x R1201N R1202x R1203x R1204x R1205x R1206N R1207N R1210N R1213K R1218x R1232D R1240x R1242S R1243x R1244N R1245x R1283K R1286K R1290K R1293K R5220x RP400x RP401x RP500x RP501K RP502x RP503x RP504x RP505K RP506K RP550K RP600K RP901K RP904Z Products With External Output Transistor RN5RK R1210N R1211x R1212D R1215D R1224N R1225N The Output Voltage Setting Ricoh has DC/DC converters types in which the output voltage is fixed internally and types that allow the output voltage to be set with external resistors. The internal types have a VOUT pin and the external types have a VFB pin. When using an externally adjustable type, please select proper components regarding to phase compensation and intrusion of noise. RP505Kxx1A/B RP505K001C (Internally fixed output voltage type) (Externally adjustable output voltage type) VIN CIN 4.7μF PVIN CE LX AVIN VOUT RP505K Series AGND L 2.2μH VOUT COUT 10μF VIN CIN 4.7μF PVIN CE LX AVIN VFB RP505K Series AGND L 2.2μH R1 R2 C1 VOUT COUT 10μF DC/DC MODE PGND MODE PGND Products With Internally Fixed Output Voltage RN5RK R1210N R1224N R1225N R1232D R1286K R5220x RP400x RP401x RP500x RP501K RP502x RP503x RP504x RP505K RP506K RP600K RP901K RP904Z Products With Externally Adjustable Output Voltage R1200x R1201N R1202x R1203x R1204x R1205x R1206N R1207N R1211x R1212D R1213K R1215D R1218x R1224N R1232D R1240x R1242S R1243x R1244N R1245x R1283K R1286K R1290K R1293K RP400K RP401K RP505K RP506K RP550K RP600K Application Note 124
Application Note The Diode Rectifier and The Synchronous Rectifier Ricoh step-down DC/DC converters can be classified into diode rectifier type and synchronous rectifier type. The diode rectifier type is uses a schottky diode, and the synchronous rectifier type uses a low side MOS transistor. In most cases, Ricoh's synchronous rectifier type DC/DC converters have built-in high side and low side MOS transistors except for the R1242S. R1240x RP500x (Diode rectifier type) (Synchronous rectifier type) CSPD 470pF R1 3.75kΩ R2 1.2kΩ VIN CIN 10μF VIN BST R1240x VFB LX GND CE VOUT=3.3V CBST 100nF L4.7μH "H"active COUT 10μF VIN CIN 10μF VIN CE AGND LX VOUT PGND 4.7μH VOUT COUT 10μF Diode Rectifier Type Step-down DC/DC Converters R1224N R1225N R1240x R1243x R1244N R1245x R1283K R1290K R1293K Synchronous Rectifier Type Step-down DC/DC Converters R1232D R1242S R1286K R5220x RP500x RP501K RP502x RP503x RP504x RP505K RP506K RP550K RP901K RP904Z The Under Voltage Lock Out Function (UVLO) To provide more stable operation some DC/DC converters contain a UVLO (Under Voltage Lock Out) function. After turning on power, the UVLO function keeps the internal circuits in the standby state until the DC/DC converter input voltage (VIN) reaches the UVLO released voltage, it is to avoid malfunctioning of the product below the UVLO voltage. In case the input voltage (VIN) drops below the UVLO detect voltage during operation, the UVLO function forces the DC/DC converter into the standby state to prevent to a malfunctioning. When the input voltage (VIN) rises above the UVLO released voltage again, the UVLO released the DC/DC converter. Products With Under Voltage Lockout Function R1200x R1201N R1202x R1203x R1204x R1205x R1206N R1207N R1211x R1212D R1213K R1215D R1218x R1224N R1225N R1232D R1240x R1242S R1243x R1244N R1245x R1283K R1286K R1290K R1293K R5220x RP500x RP501K RP502x RP503x RP504x RP505K RP506K RP550K RP901K RP904Z DC/DC The Soft Start Function The Soft Start function is initiated when the input voltage (VIN) reaches the minimum operating voltage and UVLO voltage after power on, it is to prevent that the DC/DC converter will cause a large inrush current and overshoots of output voltage. The DC/DC converter is made to start up in a smooth manner by provision of a start up time (soft start time). There are products with an internally fixed soft start time and products with externally adjustable soft start time setting pin, and products externally adjustable with an oscillator maximum duty cycle (to be explained later). Voltage Graphical view of Soft Start functions Without Soft Start function With Soft Start function Voltage Time Time Products With Soft Start Function R1200x R1201N R1202x R1203x R1204x R1205x R1206N R1207N R1211x R1212D R1213K R1215D R1224N R1225N R1232D R1240x R1242S R1243x R1244N R1245x R1283K R1286K R1290K R1293K R5220x RP400x RP401x RP500x RP501K RP502x RP503x RP504x RP505K RP506K RP550K RP600K RP901K RP904Z 125
Page 1: Application Note DC/DC Converter Ap
Page 5 and 6: Application Note The Over Voltage P
Page 7: Application Note The LED High-speed

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