RT8267GS Richtek

RT8267 2A, 22V, 400kHz Step-Down Converter General Description Features zz z zz Wide Operating Input Range : 4.75V to 22V The RT8267 is an asynchronous high voltage buck zz z zz Adjustable Output Voltage Range : 1.222V to 16V converter that can support the input voltage range from zz z zz Output Current up to 2A 4.75V to 22V and the output current can be up to 2A. zz z zz 25A Low Shutdown Current Current Mode operation provides fast transient response zz z zz Power MOSFET : 0.18 and eases loop stabilization. zz z zz High Efficiency up to 95% The chip provides protection functions such as cycle-by- zz z zz 400kHz Fixed Switching Frequency cycle current limiting and thermal shutdown protection. zz z zz Stable with Low ESR Output Ceramic Capacitors In shutdown mode, the regulator draws 25A of supply zz z zz Thermal Shutdown Protection current. The RT8267 is available in a SOP-8 surface mount zz z zz Cycle-By-Cycle Over Current Protection package. zz z zz RoHS Compliant and Halogen Free Ordering Information Applications RT8267 z Distributive Power Systems Package Type z Battery Charger S : SOP-8 z DSL Modems Lead Plating System z Pre-regulator for Linear Regulators G : Green (Halogen Free and Pb Free) Note : Pin Configurations Richtek products are : RoHS compliant and compatible with the current require- (TOP VIEW) ments of IPC/JEDEC J-STD-020. 8 BOOT NC 2 Suitable for use in SnPb or Pb-free soldering processes. 7 VIN EN 3 6 SW COMP 4 GND 5 FB SOP-8 Typical Application Circuit V 2 1 IN VIN BOOT 4.75V to 22V C C IN B L1 RT8267 10F 10nF 15H V 3 OUT SW 3.3V/2A D1 R1 Chip Enable B330 7 EN 17k C 5 OUT FB 22F C C R C R2 1.5nF 10k 10k 6 4 COMP GND C P NC DS8267-02 March 2011 www.richtek.com 1RT8267 Table 1. Recommended Component Selection V (V) R1 (k) R2 (k ) R (k ) C(nF) C (F) L1 ( H) OUT C C OUT 12 88.7 10 62 0.82 22 33 5 30 10 20 2.2 22 22 3.3 17 10 10 1.5 22 15 2.5 10.45 10 7.5 1.5 22 10 1.8 4.75 10 6 1.5 22 10 1.222 0 10 6 3.9 22 6.8 Functional Pin Description Pin No. Pin Name Pin Function High Side Gate Drive Boost Input. BOOT supplies the drive for the high side 1 BOOT N-MOSFET switch. Connect a 10nF or greater capacitor from SW to BOOT to power the high side switch. Power Input. V supplies the power to the IC, as well as the step-down converter IN 2 VIN switches. Bypass VIN to GND with a suitable large capacitor to eliminate noise on the input to the IC. Power Switching Output. SW is the switching node that supplies power to the output. 3 SW Connect the output LC filter from SW to the output load. Note that a capacitor is required from SW to BOOT to power the high side switch. Ground. The exposed pad must be soldered to a large PCB and connected to GND for 4 GND maximum power dissipation. Feedback Input. FB senses the output voltage to regulate said voltage. The feedback 5 FB reference voltage is 1.222V typically. Compensation Node. COMP is used to compensate the regulation control loop. 6 COMP Connect a series RC network from COMP to GND to compensate the regulation control loop. In some cases, an additional capacitor from COMP to GND is required. Enable Input. EN is a digital input that turns the regulator on or off. Drive EN higher than 7 EN 1.4V to turn on the regulator, lower than 0.4V to turn it off. If the EN pin is open, it will be pulled to high by internal circuit. 8 NC No Internal Connection. Function Block Diagram VIN Current Sense V CC Slope Comp Internal Amplifier Oscillator Regulator + VA 400kHz/120kHz 1A - VA V CC Foldback 10k BOOT - Control EN + S Q 1V 0.6V + SW Shutdown 3V - + Comparator R Q UV - Comparator Current GND Comparator + 1.222V EA - Gm = 780A/V FB COMP www.richtek.com DS8267-02 March 2011 2