SY7208互换的升压型DC-DC转换器MXT7515.doc

MXT7515GENERAL DESCRIPTIONThe MXT7515 is a high frequency, high efficien cy DC to DC converter with an integrated 2.8A, 0.1 Opower switch capable of providing an output voltage up to 26V.The fixed 1.2 MHz allows the use of small external inducti ons and capacitors and provides fast tran sie n t resp on se. It in tegrates Soft start, Comp. On ly n eed few comp onents outside.DSL ModemPCMCIA CardTFT LCD Bias Supply1.2MH Z,26V Step-up DC/DC Co nverterFeatures2.3V to 6V in put voltage Ran gel Efficie ncy up to 96%26V Boost co nverter with 2.8A switch curre nt1.2Mhz fixed Switch ing Freque ncyIn tegrated soft-startThermal Shutdow nUn der voltage LockoutSOT23-6 PackageAPPLICATIONSHan dheld DevicesGPS ReceiverDigital Still CameraPortable Applicatio ns#MXT7515#MXT7515#MXT7515ORDERING INFORMATIONPART NUMBERTEMP RANGESWICHING FREQUENCYILIM (A)MARKPACKAGEPINSMXT7515-40 ° C to 85° C2MHZ2.8TS02SOT23-65PIN configuration(SOT23-6)Functional Pin DescriptionPINPINNameDescripti on1LXOutput switchi ng no de. SW is the drain of the in ternal N-Cha nnel MOSFET and RDS-ON is 100m ? . Conn ect the in ductor to SW toComplete the step-up con verter.2 GNDGround.3FBRegulati on Feedback In put. Conn ect to an external resistive voltage divider from the output to FB to set the output voltage.Vfb=0.6V.4ENRegulator On/off Control In put. A logic high in put(VEN>1.4V) turns on the regulator. A logic low in put(VEN<0.4V) puts the LP6218 in to low curre nt shutdow n mode.5VinIC Power Supply.6 NCNo Conn ector.Absolute Maximum Ratings(Note: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability.)PARAMETERVALUEUNITSupply Voltage VIN-0.3 to 6.5VFB, EN Voltage-0.3 to VIN+0.3VSW VoltageVi n+0.3 to 28VVOperat ing Ambie nt Temperature-40 to 85°CMaximum Junction Temperature150°CStorage Temperature-55 to 150°CLead Temperature (Solderi ng, 10 sec)300°CELECTRICAL CHARACTERISTICS(Vin = 3.6V, Ta= 25C C unless otherwise specified)parametersymbolTEST CONDITIONSMinTYPMAXun itIn put Voltage RangeVIN2.36VBoost output voltage rangeVout26VUVLO ThresholdVUVLOVHYSTERESIS =100mV2.12.22.3VOperati ng Supply CurrentISUPPLYVFB =1.3V EN=Vin, ILoad =075135AShutdow n Supply CurrentVEN =0V, VIN =4.2V0.11Regulated Feedback VoltageVFB1.1881.21.212VPeak In ductor CurrentIPEAK2.52.83AOscillator Freque ncyFOSC0.91.21.5MHzRds(ON) of N-cha nn el FETISW =-100mA0.10.2OhmEn able ThresholdVIN = 2.3V to 5.5V0.311.5VEn able Leakage Current-0.10.11 ASW Leakage Curre ntVEN= 0V, VSW = 0V or 5V, VIN =5V11 ABLOCK DIAGRAMIT-HiB—厂F」 - * 詰 - _■ 1= EJr 1INrzvw\Figure 3 Functional Block DiagramswFUNCTIONAL DescriptionNORMAL OperationThe boost converter is designed for output voltage up to 26V with a switch peak current limit of 2.8 A. The device, which operates in a curre nt mode scheme with quasi-c on sta nt freque ncy, is exter nally 1.2MHZ and the minimum in put voltage is 2.3 V. To con trol the in rush curre nt at start-up a soft-start pin is available.During the on-time, the voltage across the in ductor causes the curre nt in it to rise. Whe n the curre nt reaches a threshold value set by the internal GM amplifier, the power transistor is turned off, the en ergy stored into the in ductor is the n released and the curre nt flows through the Schottky diode towards the output of the boost converter. The off-time is fixed for a certain Vin and Vs, and therefore mai nta ins the same freque ncy whe n vary ing these parameters.However, for different output loads, the frequency may slightly change due to the voltage drop across the Rdson of the power tran sistor which will have an effect on the voltage across the in ductor and thus on Ton (Toff rema ins fixed). Some slight freque ncy cha nges might also appear with a fixed output load due to the fact that the output voltage Vs is not sen sed directly but via the SW Pin, which affects accuracy.Because of the quasi-c on sta nt freque ncy behavior of the device , the MXT7515 elim in ates the n eed foran internal oscillator and slope compensation, which provides better stability for the system over a wide of in put and output voltages ran ge, and more stable and accurate curre nt limit ing operatio n compared to boost conv erters operat ing with a conven ti onal PWM scheme .The MXT7515 topology has also the ben efits of providi ng very good load and line regulatio ns, and excelle nt load tran sie nt resp on se.Un dervoltage lockout (uvlo)To avoid mis-operat。