RT6254BHGJ8F

® RT6254A/B 4A, 18V, 500kHz, ACOTTM Step-Down Converter General Description Features The RT6254A/B is a high-efficiency, monolithic synchronous step-down DC-DC converter that can deliver up to 4A output current from a 4.5V to 18V input supply. The RT6254A/B adopts ACOT architecture to allow the transient response to be improved and keep in constant frequency. Cycle-by-cycle current limit provides protection against shorted outputs and soft-start eliminates input current surge during start-up. Fault conditions also include output under voltage protection and thermal shutdown.  4.5V to 18V Input Voltage Range  4A Output Current Constant-on-Time Mode to Enables Fast Transient Response Low Output Ripple and Allows Ceramic Output Capacitor 500kHz Switching Frequency High Efficient Internal Power MOSFET Switch Optimized for Lower Duty Cycle Applications Integrated 48mΩ Ω/25mΩ Ω MOSFETs Adjustable Output Voltage from 0.6V to 5V Internal Soft-Start (1.5ms typ.) Built-In UVP/OTP Power Good Indicator (90%) Input Under Voltage Lockout TSOT23-6 (FC) and TSOT23-8 (FC) Packages       Ordering Information  RT6254A/B  Package Type J6F : TSOT-23-6 (FC) J8F : TSOT-23-8 (FC)   Lead Plating System G : Green (Halogen Free and Pb Free)  UVP Option H : Hiccup Applications  PSM/PWM A : PSM/PWM B : Force-PWM    Note :  Richtek products are :  Set Top Box Portable TV Access Point Router DSL Modem LCD TV 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 RT6254A/B VIN CIN BOOT VIN CBOOT L RPGOOD VOUT LX EN Enable PGOOD* AGND FB RT GND R1 CFF COUT R2 * : PGOOD pin is for TSOT23-8 (FC) package. Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6254A/B-00 August 2016 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT6254A/B Pin Configuration VIN EN GND 7 6 5 2 3 4 GND 3 LX 2 8 AGND 4 BOOT FB 5 FB 6 VIN TSOT-23-6 (FC) EN BOOT LX PGOOD (TOP VIEW) TSOT-23-8 (FC) Marking Information RT6254AHGJ6F RT6254AHGJ8F 2D= : Product Code 2D=DNN 1J= : Product Code 1J=DNN DNN : Date Code RT6254BHGJ6F RT6254BHGJ8F 1H= : Product Code 2C= : Product Code 2C=DNN DNN : Date Code 1H=DNN DNN : Date Code DNN : Date Code Functional Pin Description Pin No. Pin Name Pin Function TSOT-23-6 (FC) TSOT-23-8 (FC) 1 1 FB Feedback voltage input. This pin is used to set the desired output voltage via an external resistive divider. -- 3 AGND Analog ground. This is the signal ground reference for the IC. 2 2 EN Enable control input. Floating this pin or connecting this pin to logic high can enable the device and connecting this pin to GND can disable the device. 3 4 GND System ground. This is the power return for the IC. 4 5 VIN Power input. Supplies the power switches of the device. 5 6 LX Switch node. LX is the switching node that supplies power to the output and connect the output LC filter from LX to the output load. 6 7 BOOT Bootstrap supply for high-side gate driver. Connect a 0.1F ceramic capacitor from LX to BOOT to power the high-side switch. -- 8 PGOOD Power good indicator. Open-drain output when the output voltage is within 90% to 120% of regulation point. Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS6254A/B-00 August 2016 RT6254A/B Functional Block Diagram TSOT-23-6 (FC) BOOT VIN VIN PVCC Reg Minoff VIBIAS PVCC VREF UGATE OC Control LX Driver LGATE UV GND GND LX PVCC LX Ripple Gen. EN EN VIN + + - On-Time Comparator LX FB TSOT-23-8 (FC) BOOT VIN VIN PVCC Reg Minoff VIBIAS PVCC VREF UGATE OC Control LGATE UV GND GND LX PVCC LX Ripple Gen. EN - FB Copyright © 2016 Richtek Technology Corporation. All rights reserved. EN VIN + + On-Time Comparator DS6254A/B-00 August 2016 LX Driver LX PGOOD AGND is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT6254A/B Operation The RT6254A/B is a high-efficiency, monolithic synchronous step-down DC-DC converter that can deliver up to 4A output current from a 4.5V to 18V input supply. Using the ACOTTM control mode can reduce the output capacitance and perform fast transient response. It can minimize the component size without additional external compensation network. Current Limit The RT6254A/B current limit is a cycle-by-cycle “valley” type, measuring the inductor current through the synchronous rectifier during the off-time while the inductor current ramps down. The current is determined by measuring the voltage between Source and Drain of the synchronous rectifier, adding temperature compensation for greater accuracy. If the current exceeds the current limit, the on-time one-shot is inhibited until it drops below the current limit level. If the output current exceeds the available inductor current (controlled by the current limit mechanism), the output voltage will drop. If it drops below the output under-voltage protection level (see next section) the IC will stop switching to avoid excessive heat. External Bootstrap Capacitor Connect a 0.1μF low ESR ceramic capacitor between BOOT and LX. This bootstrap capacitor provides the gate driver supply voltage for the high side N-MOSFET switch. Over-Temperature Protection The RT6254A/B includes an Over-Temperature Protection (OTP) circuitry to prevent overheating due to excessive power dissipation. The OTP will shut down switching operation when the junction temperature exceeds 150°C. Once the junction temperature cools down by approximately 15°C, the IC will resume normal operation. For continuous operation, provide adequate cooling so that the junction temperature does not exceed 150°C. UVP Protection The RT6254A/B detects under-voltage conditions by monitoring the feedback voltage on FB pin. When the feedback voltage is lower than 60% of the target voltage, the UVP comparator will go high to turn off both internal high-side and low-side MOSFETs. Hiccup Mode The RT6254A/B use hiccup mode for UVP. When the protection function is triggered, the IC will shut down for a period of time and then attempt to recover automatically. Hiccup mode allows the circuit to operate safely with low input current and power dissipation, and then resume normal operation as soon as the overload or short circuit is removed. Input Under-Voltage Lockout 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. Shut-Down, Start-Up and Enable (EN) The enable input (EN) has a logic-low level. When VEN is below this level the IC enters shutdown mode. When VEN exceeds its logic-high level the IC is fully operational. Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS6254A/B-00 August 2016 RT6254A/B Absolute Maximum Ratings (Note 1) Supply Input Voltage, VIN ------------------------------------------------------------------------------------------------ −0.3V to 20V Enable Pin Voltage, EN --------------------------------------------------------------------------------------------------- −0.3V to 20V  Switch Node Voltage, LX -------------------------------------------------------------------------------------------------- −0.3V to 20V 