ELM620BA 1.4MHz high efficiency synchronous PWM step up DC/DC converter ■General description ELM620BA is synchronous PWM step-up DC/DC converter with high efficiency and 1.4MHz fixed frequency; by adopting synchronous switch, ELM620BA is able to provide high efficiency without external Schottky diode. ELM620BA is able to activate within the range from 0.6V to 5V of input voltage and 2.5V to 6V of output one. For 3V or 3.3V output, ELM620BA can provide current up to 260mA by a single AA cell, or to 600mA by 2 serial-connected AA cells. With 1.4MHz switching frequency, small coils and capacitors can be adopted; therefore, ELM620BA is possible to be assembled within small areas on the board . ■Features ■Application • • • • • • • • • • • • • • • • • Current mode control Output voltage drop protection Thermal shutdown protection and short circuit protection Input voltage : 0.6V to 5.0V Output voltage : 2.5V to 6.0V Low current consumption : Typ.300µA Shutdown current : < 1µA Low start-up voltage : Typ.0.9V Low switch on (internal switch) resistance : 0.35Ω Constant frequency : Typ.1.4MHz High efficiency : 96% Package : SOT-26 Cellular phone Digital camera MP3 player Portable machine Wireless handset ■Maximum absolute ratings Parameter VIN power supply voltage Apply voltage to SW Apply voltage to FB Apply voltage to EN Apply voltage to VOUT Power dissipation Operating temperature range Storage temperature range Symbol Vin Vsw Vfb Ven Vout Pd Top Tstg Limit -0.3 to +6.0 GND-0.3 to Vout+0.3 GND-0.3 to Vout+0.3 GND-0.3 to Vout+0.3 -0.3 to +6.0 250 -30 to +85 -65 to 125 Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used. Unit V V V V V mW °C °C ■Selection guide ELM620BA-S Symbol a b c Package Product version Taping direction B: SOT-26 A S: Refer to PKG file ELM620BA - S ↑↑ ↑ ab c * Taping direction is one way. 10 - 1 Rev.1.0 ELM620BA 1.4MHz high efficiency synchronous PWM step up DC/DC converter ■Pin configuration SOT-26(TOP VIEW) Pin No. 1 2 3 4 5 6 1 6 2 5 3 4 Pin name SW GND FB EN VOUT VIN Pin description Switch Ground Feedback ON/OFF control (High enable) Output Input ■Pin assignment 1) SW (Pin 1) : Switch pin. Connect inductor between SW and VIN. Keep these PCB trace lengths as short and wide as possible to reduce EMI and voltage overshoot. 2) GND (Pin 2) : Signal and power ground. Provide a short direct PCB path between GND and the (−) side of output capacitor(s). 3) FB (Pin 3) : Feedback input to gm error amplifier. Connect resistor divider tap to this pin. The output voltage can be adjusted from 2.5V to 6V by : R1 Vout = 1.203V × (1 + ) R2 4) EN (Pin 4) : Logic controlled shutdown input. EN = High: Normal free running operation, 1.4MHz typical operating frequency. EN = Low: Shutdown, quiescent current < 1μA. Output capacitor can be completely discharged through the load or feedback resistors. 5) VOUT (Pin 5) : Output voltage sense input and drain of internal synchronous rectifier MOSFET. Bias is derived from Vout. PCB trace length from Vout to output filter capacitor(s) should be as short and wide as possible. 6) VIN (Pin 6) : Battery input voltage. The device gets its start-up bias from Vin. Once Vout exceeds Vin, bias comes from Vout. Thus, once operation is started, it is completely independent from Vin and only limited by output power level and battery’s internal series resistance. 10 - 2 Rev.1.0 ELM620BA 1.4MHz high efficiency synchronous PWM step up DC/DC converter ■Standard circuit Optional schottky L=2.2µH Vin + Cin= 22µF SW VIN Vout VOUT R1= 1.02MΩ ELM620BA EN ON/OFF 1% FB Cout 22µF R2 604kΩ 1% GND Vout=(1+ R1 )×1.203 R2 ■Block diagram L 2.2µH Cin 22µF 1V to 5V Input Optional schottky Vin Vout good Start-up OSC Ramp Gen 1.4MHz A SW + � 2.3V A/B MUX PWM control Sync drive control Slope comp � 0.35Ω Cff optional ELM620BA Rc 80k Shutdown R1 1.02M 1% Current sense + Shutdown control Vout B PWM � comp � EN Vout 0.45Ω Cc 150pF 10 - 3 gm error AMP Cp2 2.5pF 1.203V ref Cout 22µF � FB + R2 604k 1% GND Rev.1.0 ELM620BA 1.4MHz high efficiency synchronous PWM step up DC/DC converter ■Electrical characteristics Parameter Output voltage range (adj.) Minimum start-up voltage Minimum operating voltage Switching frequency Maximum duty cycle Current limit delay to output Feedback voltage Feedback input current NMOS switch leakage PMOS switch leakage NMOS switch ON resistance PMOS switch ON resistance NMOS current limit Quiescent current (Active) Shutdown current EN input high EN input low EN input current Vin=1.2V, Vout=3.3V, Top=25°C, unless otherwise noted Symbol Condition Min. Typ. Max. Unit Vout 2.5 6.0 V Vst Iload=1mA 0.9 1.1 V Vin EN=Vin 0.60 0.75 V Fsw 1.1 1.4 1.7 MHz Dmax Vfb=1.15V 80 87 % tllimdly 40 ns Vfb 1.165 1.203 1.241 V Ifb Vfb=1.22V 1 nA IleakN Vsw=5V 0.1 5.0 µA Vsw=0V 0.1 5.0 µA IleakP 0.35 Ω RswN Vout=3.3V Vout=3.3V 0.45 Ω RswP IlimN 700 950 mA Iq Measured on Vout, Non-switching 300 500 µA Is Ven=0V, Including switch leakage 0.1 1.0 µA Venh 1 V Venl 0.35 V Ien Ven=5.5V 0.01 1.00 µA ■Test circuits L=2.2µH SBD SW VIN Vout VOUT ELM620BA Vin FB EN GND Cin=22µF Cout= 22µF R1 RL R2 10 - 4 Rev.1.0 ELM620BA 1.4MHz high efficiency synchronous PWM step up DC/DC converter ■Application notes 1) PCB layout guidelines The high speed operation of ELM620BA demands careful attention to board layout, and in order to get advertised performance, a well-planned layout is required. Figure-1 is an example which shows the recommended component placement with optional Schottky diode. A large ground pin copper area will help to lower the chip temperature. A multilayer board with a separate ground plane is ideal, but not absolutely necessary. Fig-1 Vin 1 SW VIN 6 2 GND VOUT 5 3 FB 4 EN EN Vout Figure 1: Recommended component placement for single layer board with optional Schottky diode. Traces carrying high current are direct. Trace area at FB pin is small. Lead length to battery is short. 2) Inductor selection ELM620BA can utilize small surface mount and chip inductors due to its fast 1.4MHz switching frequency. Typically, a 2.2μH inductor is recommended for most applications; larger values of inductance will allow greater output current capability by reducing the inductor ripple current. Increasing the inductance above 10μH will increase size while providing little improvement in output current capability. Iout(max) = η × (Ip − Vin×D ) × (1 − D) 2×f×L where: η = estimated efficiency Ip = peak current limit value (0.7A) Vin = input (battery) voltage D = steady-state duty ratio = (Vout − Vin) / Vout f = switching frequency (1.4MHz typical) L = inductance value The inductor current ripple is typically set for 20% to 40% of the maximum inductor current (IP). High frequency ferrite core inductor materials reduce frequency dependent power losses compared to cheaper powdered iron types. The inductor should have low ESR (series resistance of the windings) to reduce the I2R power losses, and must be able to handle the peak inductor current without saturating. Molded chokes and some chip inductors usually do not have enough core to support the peak inductor currents of 950mA seen on ELM620BA. To minimize radiated noise, ELM recommends using a toroid, pot core or shielded bobbin inductor. See Table for some suggested components and suppliers. Table : Recommended inductors. L Part (μH) CDRH3D16 2.2 CDH3B16 2.2 Max. DCR (mΩ) 75 70 Max. DC current (A) 1.2 1.2 10 - 5 Size: W × L × H (mm3) 3.8×3.8×1.8 4.0×4.0×1.8 Vendor Sumida Ceaiya Rev.1.0 ELM620BA 1.4MHz high efficiency synchronous PWM step up DC/DC converter 3) Output and input capacitor selection Low ESR (equivalent series resistance) capacitors should be used to minimize the output voltage ripple. Multilayer ceramic capacitors are an excellent choice, as they have extremely low ESR and are available in small footprints. A 4.7μF to 22μF output capacitor is sufficient for most applications; larger values up to 22μF may be used to obtain extremely low output voltage ripple and improve transient response. An additional phase lead capacitor may be required with output capacitors larger than 10μF to maintain acceptable phase margin. X5R and X7R dielectric materials are preferred for their ability to maintain capacitance over wide voltage and temperature ranges. Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. It follows that ceramic capacitors are also a good choice for input decoupling and should be located as closely as possible to the device. A 10μF input capacitor is sufficient for virtually any application. Larger values may be used without limitations. ■Marking SOT-26 � abcde a to e : Assembly lot No. A to Z (I, O, X excepted) and 0 to 9 10 - 6 Rev.1.0 ELM620BA 1.4MHz high efficiency synchronous PWM step up DC/DC converter ■Typical characteristics • V=3.3V • Vout=3.3V : Cin=22µF, Cout=22µF, L=2.2µH, R1=46.6kΩ, R2=26.7kΩ, Top=25°C Vout-Vin 4.0 Vout (V) EFFICIENCY (%) 3.5 Iout=1mA 3.0 100mA 2.5 EFFICIENCY-Iout 100 10mA 2.0 1.5 1.0 80 Vin=3V 60 Vin=2.4V Vin=1.8V 40 Vin=1.5V 20 0.5 0 0.5 1.5 1 2 2.5 0 0.1 3 1000 Iout (mA) Vin (V) Vout-Iout 4 100 10 1 Vhold-Iout 0.7 0.6 Vin=3V Vhold (V) Vout (V) 3 Vin=2.4V Vin=1.8V 2 Vin=1.5V 0.5 0.4 0.3 0.2 1 1 10 Iout (mA) 100 0.1 1000 10 - 7 0 10 20 30 Iout (mA) 40 50 Rev.1.0 ELM620BA 1.4MHz high efficiency synchronous PWM step up DC/DC converter Vout-Top 1.2 3.34 1.1 3.32 Vout (V) Vst (V) Vst-Iout 1.0 0.9 0.8 3.30 3.28 0 3.5 10 20 30 40 3.26 -40 50 -20 0 20 40 60 Iout (mA) Top (�) Start Response Load Transient Response Vin=Ven=1.8V, No load Vout (V) 3 2 80 Vin=1.8V, Iout=0.1mA�0.1A 3.5 3.4 3.3 3.2 1 0 0.1 1 0 Iout (A) 2 Ven (V) Vout (V) Vin=1.5V, Iout=0.1A 0 0 0 0.4 0.8 1.2 1.6 2 2.4 2.8 3.2 3.6 4 2 4 6 8 10 12 14 16 18 20 Time (ms) Time (ms) 10 - 8 Rev.1.0 ELM620BA 1.4MHz high efficiency synchronous PWM step up DC/DC converter • V=5.0V • Vout=5.0V : Cin=22µF, Cout=22µF, L=2.2µH, R1=68.5kΩ, R2=21.7kΩ, Top=25°C Vout-Vin 6.0 Iout=1mA EFFICIENCY (%) Vout (V) 5.0 4.0 100mA 3.0 10mA 2.0 1.0 0 0.5 1 1.5 2 EFFICIENCY-Iout 100 2.5 3 3.5 Vin=3V 80 60 Vin=1.8V 40 20 0 0.1 4 1 Vin (V) Vout-Iout 6 0.8 4 Vhold (V) Vout (V) 100 Vhold-Iout 0.9 5 Vin=3V Vin=1.8V 3 2 1 10 Iout (mA) 0.7 0.6 0.5 0.4 1 10 0.3 100 Iout (mA) 10 - 9 0 10 20 30 Iout (mA) 40 50 Rev.1.0 ELM620BA 1.4MHz high efficiency synchronous PWM step up DC/DC converter Vout-Top Vst-Iout 1.2 5.05 Vout (V) 1.0 0.9 4.95 0 10 20 30 40 4.90 -40 50 -20 0 20 40 60 Iout (mA) Top (�) Start Response Load Transient Response Vin=Vec=3V, No load 6 Vout (V) 4 3 2 80 Vin=3V, Iout=0.1mA�0.1A 5.25 5 5.125 5 4.875 1 0.1 0 3 2 1 Ven (V) Vout (V) 5.00 0 0 0 0.2 0.4 0.6 0.8 0 1 2 4 6 Iout (A) Vst (V) 1.1 0.8 Vin=3V, Iout=0.1A 5.10 8 10 12 14 16 18 20 Time (ms) Time (ms) 10 - 10 Rev.1.0