RT7255CGV8

RT7255 1.5A, 18V, 500kHz ACOTTM Synchronous Step-down Converter Features General Description The RT7255 is a synchronous step-down converter with Advanced Constant On-Time (ACOTTM) mode control. The ACOTTM provides a very fast transient response with few external components. The low impedance internal MOSFET supports high efficiency operation with wide input voltage range from 4.3V to 18V. The proprietary circuit of the RT7255 supports all ceramic capacitors. The output voltage can be adjusted between 0.6V and 8V. Ordering Information             Input Under-Voltage Lockout Hiccup Mode Under-Voltage Protection  Thermal Shutdown  RT7255 Package Type V8 : SOT-23-8 4.3V to 18V Input Voltage Range Adjustable Soft-Start Time PGOOD Function 1.5A Output Current Advanced Constant On-Time Control Fast Transient Response Support All Ceramic Capacitors Up to 95% Efficiency 500kHz Switching Frequency Adjustable Output Voltage from 0.6V to 8V Cycle-by-Cycle Current Limit Applications Lead Plating System G : Green (Halogen Free and Pb Free)  A : Hiccup + PSM B : Non-UVP + PSM C : Hiccup + PWM D : Non-UVP + PWM     Industrial and Commercial Low Power Systems Computer Peripherals LCD Monitors and TVs Green Electronics/Appliances Point of Load Regulation for High-Performance DSPs, FPGAs, and ASICs Note : Richtek products are :  RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.  Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit L RT7255 VIN VIN VOUT SW CBOOT CIN BOOT RPG CFF R1 COUT PGOOD 5V EN Enable SS FB R2 GND CSS Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7255-00 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT7255 Pin Configurations Marking Information EN PGOOD 0B=DNN VIN RT7255AGV8 SW (TOP VIEW) 8 7 6 5 0B= : Product Code DNN : Date Code RT7255BGV8 0A=DNN SS GND BOOT 4 RT7255CGV8 FB 3 2 0A= : Product Code DNN : Date Code 09=DNN 09= : Product Code DNN : Date Code SOT-23-8 RT7255DGV8 06=DNN 06= : Product Code DNN : Date Code Functional Pin Description Pin No. Pin Name Pin Function 1 BOOT Bootstrap Supply for High-Side Gate Driver. Connect a 1F ceramic capacitor between the BOOT and SW pins. 2 GND Power Ground. 3 SS Soft-Start Time Setting. Connect a capacitor from SS to GND to set the soft-start period. 4 FB Feedback Voltage Input. The pin is used to set the output voltage of the converter via a resistive divider. The converter regulates VFB to 0.6V. 5 PGOOD Power Good Indicator Output. 6 EN Enable Control Input. Connect EN to a logic-high voltage to enable the IC or to a logic-low voltage to disable. Do not leave this high impedance input unconnected. 7 VIN Power Input. The input voltage range is from 4.3V to 18V. Must bypass with a suitable large ceramic capacitor at this pin. 8 SW Switch Node. Connect to external L-C filter. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS7255-00 June 2015 RT7255 Function Block Diagram BOOT VIN PVCC Reg VIBIAS Min. Off PVCC VIN VREF UGATE Control OC Driver SW LGATE UV & OV GND SW PVCC SW Ripple Gen. SS FB VIN SW PGOOD + Comparator On-Time GND PWRGN EN EN Operation The RT7255 is a synchronous step-down converter with advanced constant on-time control mode. Using the ACOT control mode can reduce the output capacitance and fast transient response. It can minimize the component size without additional external compensation network. UVLO Protection To protect the chip from operating at insufficient supply voltage, the UVLO is needed. When the input voltage of VIN is lower than the UVLO falling threshold voltage, the device will be lockout. Thermal Shutdown Current Protection When the junction temperature exceeds the OTP The inductor current is monitored via the internal switches cycle-by-cycle. Once the output voltage drops under UV threshold, the RT7255 will enter hiccup mode. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS7255-00 June 2015 threshold value, the IC will shut down the switching operation. Once the junction temperature cools down and is lower than the OTP lower threshold, the converter will autocratically resume switching. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT7255 Absolute Maximum Ratings (Note 1)  VIN to GND ------------------------------------------------------------------------------------------------------------- 0.3V to 20V  SW to GND ------------------------------------------------------------------------------------------------------------- 0.3V to 20V