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| YB1680 1.5MHz, 600mA Synchronous Step-Down Converter Description The YB1680 is a 1.5MHz constant frequency, slope compensated current mode PWM step-down converter. The device integrates a main switch and a synchronous rectifier for high efficiency without an external Schottky diode. It is ideal for powering portable equipment that runs from a single cell lithium-Ion (Li+) battery. The YB1680 can supply 600mA of load current from a 2.5V to 5.5V input voltage. The output voltage can be regulated as low as 0.6V. The YB1680 can also run at 100% duty cycle for low dropout operation, extending battery life in portable system. Idle mode operation at light loads provides very low output ripple voltage for noise sensitive applications. The YB1680 is offered in a low profile 5-pin, SOT package, and is available in an adjustable version. Features High Efficiency : Up to 94% 1.5MHz Constant Switching Frequency 600mA Output Current at VIN=3V Integrated Main Switch and Synchronous Rectifier. No Schottky Diode Required 2.5V to 5.5V Input Voltage Range Output Voltage as Low as 0.6V 100% Duty Cycle in Dropout Low Quiescent Current : 300A Slope Compensated Current Mode Control for Excellent Line and Load Transient Response Short Circuit Protection Thermal Fault Protection <1A Shutdown Current Space Saving 5-Pin SOT23 Package Pb-free Package Applications Cellular and Smart Phones Microprocessors and DSP Core Supplies Wireless and DSL Modems PDAs MP3 Player Digital Still and Video Cameras Portable Instruments Typical Application Circuit Figure 1: Typical Application Circuit YB1680 Rev.1.0 www.yobon.com.tw 1 YB1680 1.5MHz, 600mA Synchronous Step-Down Converter Pin Configuration EN GND SW 1 2 3 SOT23-5 5 4 FB VIN Figure 2: Pin Configuration Pin Description Table 1 Pin 1 2 3 Name EN GND SW Description Regulator Enable control input. Drive EN above 1.5V to turn on the part. Drive EN below 0.3V to turn it off. In shutdown, all functions are disabled drawing <1A supply current. Do not leave EN floating. Ground. Power Switch Output. It is the Switch note connection to Inductor. This pin connects to the drains of the internal P-CH and N-CH MOSFET switches. Supply Input Pin. Must be closely decoupled to GND, Pin 2, with a 2.2F or greater ceramic capacitor. VFB (Adjustable Version) : Feedback Input Pin. Connect FB to the center point of the external resistor divider. The feedback threshold voltage is 0.6V. 4 VIN 5 FB Ordering Information Order Number YB1680ST25XADJP Package Type SOT23-5 Supplied As 3000 units Tape & Reel Package Marking A1XY (Note 1) Note 1: XY = Manufacturing Date Code YB1680 Rev.1.0 www.yobon.com.tw 2 YB1680 1.5MHz, 600mA Synchronous Step-Down Converter Absolute Maximum Ratings Input Supply Voltage ................... -0.3V to 6V EN, VFB Voltage ................ -0.3V to VIN+0.3V SW, VOUT Voltage.............. -0.3V to VIN+0.3V Peak SW Sink and Source Current........1.5A Operating Temperature Range.. -40C to 85C Junction Temperature ....................... 125C Storage Temperature Range ... -65C to 150C Lead Temperature (Soldering, 10s) .. 300C Electrical Characteristics Table 2 (VIN = VRUN = 3.6V, TA=25C, Test Circuit Figure 1, unless otherwise noted.) Description Input Voltage Range Input DC Supply Current Active Mode Shutdown Mode Symbol VIN IQ VFB = 0.5V VFB = 0V, VIN = 4.2V TA = +25 Regulated Feedback Voltage VFB TA = 0 TA 85 TA = -40 TA 85 VFB Input Bias Current Reference Voltage Line Regulation Output Voltage Line Regulation Output Voltage Load Regulation Maximum Output Current Oscillator Frequency RDS(ON) of P-CH MOSFET RDS(ON) of N-CH MOSFET Peak Inductor Current FOSC IFB VFB = 0.65V VFB = 2.5V to 5.5V, VOUT = VFB (R2=0) VIN = 2.5V to 5.5V, IOUT = 10mA IOUT from 0 to 600mA VIN = 3.0V VFB = 0.6V or VOUT = 100% ISW = 300mA ISW = -300mA VIN = 3V, VFB = 0.5V or VOUT = 90% Duty Cycle < 35% VRUN = 0V, VSW = 0V or 5V, VIN = 5V VOVL = VOVL - VFB VEN IEN -40 TA 85 0.3 600 1.2 1.5 0.30 0.20 1.20 1.8 0.50 0.45 0.11 0.11 0.0015 0.5880 0.5865 0.5850 Test Conditions MIN 2.5 270 0.08 0.6000 0.6000 0.6000 TYP MAX 5.5 400 1.0 0.6120 0.6135 0.6150 30 0.63 0.63 nA %/V %/V %/mA mA MHz A V Units V A SW Leakage Output Over Voltage Lockout EN Threshold EN Leakage Current 0.01 60 0.45 0.1 1 A mV 1.30 1 V A YB1680 Rev.1.0 www.yobon.com.tw 3 YB1680 1.5MHz, 600mA Synchronous Step-Down Converter Typical Performance Characteristics YB1680 Rev.1.0 www.yobon.com.tw 4 YB1680 1.5MHz, 600mA Synchronous Step-Down Converter YB1680 Rev.1.0 www.yobon.com.tw 5 YB1680 1.5MHz, 600mA Synchronous Step-Down Converter YB1680 Rev.1.0 www.yobon.com.tw 6 YB1680 1.5MHz, 600mA Synchronous Step-Down Converter Function Block Figure 3: Function Block Operation YB1680 is a monolithic switching mode Step-Down DC-DC converter. It utilizes internal MOSFETs to achieve high efficiency and can generate very low output voltage by using internal reference at 0.6V. It operates at a fixed switching frequency, and uses the slope compensated current mode architecture. This Step-Down DC-DC Converter supplies 600mA output current at VIN = 3V with input voltage range from 2.5V to 5.5V. Current Mode PWM Control Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for excellent load and line responses and protection of YB1680 Rev.1.0 the internal main switch (P-Ch MOSFET) and synchronous rectifier (N-CH MOSFET). During normal operation, the internal P-Ch MOSFET is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. The current comparator, ICOMP, limits the peak inductor current. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until either the inductor current starts to reverse, as indicated by the current reversal comparator, IZERO, or the beginning of the next clock cycle. The OVDET comparator controls output transient overshoots by 7 www.yobon.com.tw YB1680 1.5MHz, 600mA Synchronous Step-Down Converter turning the main switch off and keeping it off until the fault is no longer present. Idle Mode Operation At very light loads, the YB1680 switch and synchronous rectifier. The slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles greater than 50%. Conversely the current limit increases as the duty cycle decreases. automatically enters Idle Mode. In the Idle Mode, the inductor current may reach zero or reverse on each pulse. The PWM control loop will automatically skip pulses to maintain output regulation. The bottom MOSFET is turned off by the current reversal comparator, IZERO, and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the switching regulator. Dropout Operation When the input voltage decreases toward the value of the output voltage, the YB1680 allows the main switch to remain on for more than one switching cycle and increases the duty cycle until it reaches 100%. The output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. At low input supply voltage, the RDS(ON) of the P-Channel MOSFET increases, and the efficiency of the converter decreases. Caution must be exercised to ensure the heat dissipated not to exceed the maximum junction temperature of the IC. Application Information Setting the Output Voltage Figure 1 above shows the basic application circuit with YB1680 adjustable output version. The external resistor sets the output voltage according to the following equation: R1=300K for all outputs; R2=300K for VOUT=1.2V, R2=200K for VOUT=1.5V, R2=150K for VOUT=1.5V, and R=95.3K for VOUT=2.5V. Inductor Selection For most designs, the YB1680 operates with inductors of 1H to 4.7H. Low inductance values are physically smaller but require faster switching, which results in some efficiency loss. The inductor value can be derived from the following equation: Maximum Load Current The YB1680 will operate with input supply voltage as low as 2.5V, however, the maximum load current decreases at lower input due to large IR drop on the main YB1680 Rev.1.0 Where IL is inductor Ripple Current. Large value inductors lower ripple current and small value inductors result in high ripple currents. Choose inductor ripple current 8 www.yobon.com.tw YB1680 1.5MHz, 600mA Synchronous Step-Down Converter approximately 35% of the maximum load current 600mA, or IL = 210mA. For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor is 2.2H. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in the 50m to 150m range. For higher efficiency at heavy loads (above 200mA), or minimal load regulation (but some transient overshoot), the resistance should be kept below 100m. 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 (600mA+105mA). Input Capacitor Selection The input capacitor reduces the surge current drawn from the input and switching noise from the device. The input capacitor impedance at the switching frequency shall be less than input source impedance to prevent high frequency switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must be used. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. A 4.7F ceramic capacitor for most applications is sufficient. Output Capacitor Selection The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. The output capacitor must have low impedance at the switching frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their low ESR and high ripple current. The output ripple VOUT is determined by: YB1680 Rev.1.0 www.yobon.com.tw 9 YB1680 1.5MHz, 600mA Synchronous Step-Down Converter Package Information (SOT23-5) NOTICE: The information described herein is subject to change without notice. Yobon does not assume any responsibility for use of any circuitry or applications described herein, nor does it convey any patent license. YB1680 Rev.1.0 www.yobon.com.tw 10 |
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