800mA Synchronous Buck Switching Regulator

Transcription

1 800mA Synchronous Buck Switching Regulator Product Description The is a step-down, current mode, DC-DC converter. At heavy load, the constant-frequency PWM control performs excellent stability and transient response. To ensure the longest battery life in portable applications. The is supported with a range of input voltages from 2.5V to 5V. The output voltage is adjustable from 0.6V to the input voltage. include internal power switch and synchronous rectifier for minimal external part count and high efficiency. During the shutdown, the input is disconnected from the output and the shutdown current is less than 0.1µA. Other key features include under-voltage lockout to prevent deep-battery discharge and soft-start to prevent input current overshoot at startup. The is available in SOT-23-5 package. Features Efficiency up to 93% Only 40uA(TYP.) Quiescent Current Internal Synchronous Rectifier 1.5MHz Switching Frequency Under-Voltage Lockout Soft-Start Short Circuit Protection 5-pin Small SOT-23-5 Package Pb-Free Package Applications Cellular phone Portable electronics Wireless Devices Cordless phone Computer peripherals Battery Powered Widgets Electronic scales Block Diagram Vin IAMP + - FB EN Rfb1 Rfb2 1.5M OSC FREQ SHIFT VIN 0.6V Vref SLOPE COMP - EA + COMP OSC + - PWM COMP SQ RQ RS LATCH Switching Logic Blanking Circuit ANTISHOOT THRU IRCMP + - High Side MOS-FET Low Side MOS-FET SW GND SHUTDOWN 1

2 Packages & Pin Assignments Adjustable Version Pin No. Symbol Description 1 EN Enable (Active High) 2 GND Ground 3 SW Switch 4 V IN Input 5 FB Feedback Ordering Information GS Complete P/N Voltage Package Marking Q ty / Reel LF Adjustable SOT-23-5L FAV YWG 3000 Pcs *For other output voltages, please contact factory Marking Information BA: GS P/N V: Voltage Code BA V YW YW: Date Code 2

3 Absolute Maximum Ratings Symbol Parameter Maximum Rating Units V IN Supply Voltage V SS to V SS +6 V V SW SW Pin Voltage V SS to V IN V P D Power T A = 25ºC 0.4 W θ JA Thermal Resistance Junction to Ambient 250 ºC/W θ JC Thermal Resistance Junction to Case 130 ºC/W T A Operating Ambient Temperature Range 0 to 85 ºC T J Operating Junction Temperature Range 0 to 125 ºC T STG Storage Temperature Range -65 to 125 ºC T LEAD Lead Temperature (Soldering, 5 Sec). 300 ºC These are stress rating only and functional operation is not implied. Exposure to absolute maximum rating for prolonged time periods may affect device reliability. All voltage are with respect to ground. Electrical Characteristics T A =25ºC, V IN =5V, V OUT =1.8V, C IN =10uF, C OUT =10uF, L=4.7uH, unless otherwise noted. Symbol Parameter Test Conditions Min Typ Max Unit V IN Input Voltage V V FB ΔV FB V OUT I PK REG LINE REG LOAD Regulated Feedback Voltage Reference Voltage Line Regulation Regulated Output Voltage Accuracy Peak Inductor Current Output Voltage Line Regulation Output Voltage Load Regulation V %/ V I OUT = 100 ma % V IN =3V, V FB =0.5V or V OUT =90% 0.9 A V IN =2.5V to 5V, I OUT =10mA 0.5 %/ V I OUT = 1mA to 800mA 0.5 % I Q Quiescent Current No Load ua I SD Shutdown Current V EN =0V ua f OSC R DS(ON) Oscillator Frequency Drain-Source On-State Resistance V OUT =100% 1.5 MHz V FB=0V or V OUT =0V 500 KHz I DS =100mA P MOSFET 0.3 N MOSFET I LSW SW Leakage Current - ±0.01 ua V EH EN Threshold High V V EL EN Threshold Low V I EN EN Leakage Current - ±0.01 ua Note: V OUT (S) specified above is the set output voltage value, and V OUT is the typical value of the actual output. 0.3 Ω 3

4 Typical Application Circuit V OUT = V REF x ( 1 + Rfb1/Rfb2 ) Adjustable Voltage Version Typical Performance Characteristics T A =25ºC, C IN =10uF, C OUT =10uF, L=4.7uF, unless Otherwise noted Efficiency vs. Output Current (Vo=1.2V) Efficiency vs. Output Current (Vo=1.5V) Efficiency vs. Output Current (Vo=1.8V) Efficiency vs. Output Current (Vo=2.5V) 4

5 Typical Performance Characteristics(continue) Efficiency vs. Output Current (Vo=2.8V) Efficiency vs. Input Voltage (Vo=1.2V) Efficiency vs. Input Voltage (Vo=1.5V) Efficiency vs. Input Voltage (Vo=1.8V) Efficiency vs. Input Voltage (Vo=2.5V) Efficiency vs. Input Voltage (Vo=2.8V) 5

6 Typical Performance Characteristics (Continue) T A =25ºC, C IN =10uF, C OUT =10uF, L=4.7uF, unless Otherwise noted Load Transient Io=0-800mA ; Vo=1.8V ; Vin=3.6V Load Transient Io=50-800mA ; Vo=1.8V ; Vin=3.6V Load Transient Io= mA ; Vo=1.8V ; Vin=3.6V Start-up from Shutdown Vo=1.8 V ; Vin=3.6V Application Information The basic application circuit is shown in Page3. External component selection is determined by the load requirement, selecting L first and then C IN and C OUT. Inductor Selection For most applications, the value of the inductor will fall in the range of 1μH to 4.7μH. Its value is chosen based on the desired current. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher V IN or V OUT also increases the ripple current as shown in equation 1. A reasonable starting point for setting ripple current is I=240mA (40% of 600mA). The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. Thus, a 720mA rated inductor should be enough for most applications (600mA +120mA).For better efficiency, choose a low DC-resistance inductor. 6

7 Application Information (Continue) C IN and C OUT Selection In continuous mode, the source current of the top MOSFET is a square wave of duty cycle V OUT / V IN. To prevent large voltage transients, a low ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given by: This formula has a maximum at V IN = 2V OUT, where I RMS =I OUT / 2. This simple worst-case condition is commonly used for design because Even significant deviations do not offer much relief. Note that the capacitor manufacturer's ripple current ratings are often based on 2000 hours of life. This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Consult the manufacturer if there is any question. The selection of C OUT is driven by the required effective series resistance (ESR). Typically, once the ESR requirement for C OUT has been met, the RMS current rating generally far exceeds the I RIPPLE (P-P) requirement. The output ripple ΔV OUT is determined by: Where f = operating frequency, C OUT =output capacitance and ΔI L = ripple current in the inductor. For a fixed output voltage, the output ripple is highest at maximum input voltage since ΔI L increases with input voltage. Using Ceramic Input and Output Capacitors Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. Using ceramic capacitors can achieve very low output ripple and small circuit size. When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage characteristics of all the ceramics for a given value and size. PCB Layout Check List When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the. These items are also illustrated graphically in Figure 1. Check the following in your layout: 1. The power traces, consisting of the GND trace, the SW trace and the V IN trace should be kept short, direct and wide. 2. Does the V FB pin connect directly to the feedback resistors? The resistive divider R1/R2 must be connected between the (+) plate of C OUT and ground. 3. Does the (+) plate of C IN connect to V IN as closely as possible? This capacitor provides the AC current to the internal power MOSFETs. 4. Keep the switching node, SW, away from the sensitive V FB node. 5. Keep the ( ) plates of C IN and C OUT as close as possible. Figure 1: Suggested Layout 7

8 Package Dimension SOT-23-5L D e1 E G E1 e b L (L1) θ A A2 c A1 Dimensions SYMBOL Millimeters Inches MIN MAX MIN MAX A A A b c D E E e 0.95 (TYP).037 (TYP) e (TYP).075 (TYP) L L (TYP).024 (TYP) G 0.25 (TYP).010 (TYP) θ

9 NOTICE Information furnished is believed to be accurate and reliable. However Globaltech Semiconductor assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties, which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Globaltech Semiconductor. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information without express written approval of Globaltech Semiconductor. CONTACT US GS Headquarter 4F.,No.43-1,Lane11,Sec.6,Minquan E.Rd Neihu District Taipei City 114, Taiwan (R.O.C) Wu-Xi Branch No.21 Changjiang Rd., WND, Wuxi, Jiangsu, China (INFO. &. TECH. Science Park Building A 210 Room) sales_cn@gs-power.com 824 Bolton Drive Milpitas. CA RD Division Version_1.3 Notice