RT8259GJ6 Richtek

RT8259 1.2A, 24V, 1.4MHz Step-Down Converter General Description Features zz z zz Wide Operating Input Voltage Range : 4.5V to 24V The RT8259 is a high voltage buck converter that can support zz z zz Adjustable Output Voltage Range : 0.8V to 15V the input voltage range from 4.5V to 24V and the output zz z zz 1.2A Output Current current can be up to 1.2A. Current Mode operation provides zz z zz 0.3 Internal Power MOSFET Switch fast transient response and eases loop stabilization. zz z zz High Efficiency up to 92% The chip also provides protection functions such as cycle- zz z zz 1.4MHz Fixed Switching Frequency by-cycle current limiting and thermal shutdown protection. zz z zz Stable with Low ESR Output Ceramic Capacitors The RT8259 is available in a SOT-23-6 and TSOT-23-6 zz z zz Thermal Shutdown packages. zz z zz Cycle-By-Cycle Over Current Protection zz z zz RoHS Compliant and Halogen Free Ordering Information RT8259 Applications Package Type z Distributed Power Systems E : SOT-23-6 z Battery Charger J6 : TSOT-23-6 z Pre-Regulator for Linear Regulators Lead Plating System z WLED Drivers G : Green (Halogen Free and Pb Free) Note : Pin Configurations Richtek products are : (TOP VIEW) RoHS compliant and compatible with the current require- ments of IPC/JEDEC J-STD-020. PHASE VIN EN Suitable for use in SnPb or Pb-free soldering processes. 6 5 4 23 Marking Information BOOT GND FB For marking information, contact our sales representative SOT-23-6/TSOT-23-6 directly or through a Richtek distributor located in your area. Typical Application Circuit V IN 4.5V to 24V V 5 1 OUT VIN BOOT 3.3V C1 L1 CB RT8259 10F 4.7H 10nF 6 PHASE D1 R1 Chip Enable B230A 4 62k EN 3 C2 FB 22F Open = GND R2 Automatic Startup 2 19.6k DS8259-03 March 2011 www.richtek.com 1RT8259 Table 1. Recommended Component Selection, C2 = 22F V (V) 1.2 1.8 2.5 3.3 5 8 10 15 OUT L1 ( H) 2 2 3.6 4.7 6.8 10 10 15 R1 (k ) 62 62 62 62 62 68 68 68 R2 (k ) 124 49.9 29.4 19.6 12 7.5 5.9 3.9 Functional Pin Description Pin No. Pin Name Pin Function Bootstrap. A capacitor is connected between PHASE and BOOT pins to form a floating 1 BOOT supply across the power switch driver. This capacitor is needed to drive the power switchs gate above the supply voltage. Ground. This pin is the voltage reference for the regulated output voltage. For this reason, 2 GND care must be taken in its layout. This node should be placed outside of the D1 to C1 ground path to prevent switching current spikes from inducing voltage noise into the part. Feedback. An external resistor divider from the output to GND tapped to the FB pin sets the 3 FB output voltage. The value of the divider resistors also set loop bandwidth. 4 EN Chip Enable (Active High). If the EN pin is open, it will be pulled to high by internal circuit. Supply Voltage. Bypass VIN to GND with a suitable large capacitor to prevent large voltage 5 VIN spikes from appearing at the input. 6 PHASE Switch Output. Function Block Diagram VIN - X20 1A + Current Sense Amp 25m Ramp Regulator Generator BOOT - 1.1V 10k Oscillator + EN 1.4MHz Shutdown S Reference 3V Comparator Q Driver + + R EA - PHASE FB - PWM Comparator 30pF Bootstrap 400k Control OC Limit Clamp GND 1pF www.richtek.com DS8259-03 March 2011 2