ELM605DA 2A synchronous step-down DC/DC converter ■General description ELM605DA is low-input voltage and high-output current synchronous-buck PWM converter and integrates with all required active components. Its' operating input voltage ranges from 2.5V to 6V and output voltage ranges from Vin down to 0.8V. ELM605DA operates at a fixed switching frequency of 1.0MHz. In addition, it provides internal soft-start to reduce inrush-current, current-limit and thermal shutdown, preventing IC from being damaged and improving design reliability. Open-drain power good monitors the output voltage. ■Features ■Application • • • • • • • • • • • • • • • • • • Current mode operation Power good function monitoring output voltage Internal soft start Thermal shutdown Current-limit and short-circuit protection Input voltage range : 2.5V to 6.0V Output current : 2A Low quiescent current (active mode) : 200μA Output voltage range (adj.) : 0.8V to Vin Shutdown current : 7μA High efficiency : 95% Constant frequency operation : 1.0MHz Package : SOP-8 ASIC/DSP/μP/FPGA core and I/O voltages Networking and telecommunications TV Set top boxes Cellular base stations ■Maximum absolute ratings Parameter VIN power supply voltage Apply voltage to SW Apply voltage to EN Apply voltage to FB Power dissipation Operating temperature range Storage temperature range Symbol Vin Vsw Ven Vfb Pd Top Tstg Limit -0.3 to +6.5 -0.3 to Vin+0.3 -0.3 to Vin -0.3 to Vin 300 -40 to +150 -65 to +150 Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used. Unit V V V V mW °C °C ■Selection guide ELM605DA-S Symbol a b c Package Product version Taping direction D: SOP-8 A S: Refer to PKG file ELM605DA - S ↑↑ ↑ ab c * Taping direction is one way. 13 - 1 Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter ■Pin configuration SOP-8(TOP VIEW) 1 8 2 7 3 6 4 5 Pin No. 1 2 3 4 5 6 7 8 Pin name VCC PG GND FB EN PGND SW VIN Pin description Supply voltage input Power good Ground Feedback/Output voltage Enable input Power switch ground Power switch output Power switch supply voltage input ■Standard circuit ELM605DA Vin 8 10µF 100k 10 1 VIN PG 100k 2.2µH VCC SW 0.1µF 5 PG 2 EN PGND FB GND 6 Vout 7 22µF 4 R1 Cup* (option) R2 3 Vout=0.8V*(1+R1/R2) ■Block diagram VCC VIN 500k ohm + Current sence amplifier Reference 0.8V FB + - + Error amplifier Oscillator 0.72V PWM comparator Clock + - PWM logic SW GND 13 - 2 M2 LG DCC PG M1 UG Zero-current comparator + - Slop comp + EN PGND Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter ■DC electrical characteristics Vin=3.3V, Top=25°C, unless otherwise noted Parameter Symbol Test condition Min. Typ. Max. Unit Supply voltage Vin 2.5 6.0 V Quiescent current Iout=0mA, no switching 220 µA Iq Shutdown current EN=GND 7 µA Is Adjustable output voltage range 0.8 Vin V Vout Regulated feedback voltage Top=+25°C 0.784 0.800 0.816 V Vfb Output voltage line regulation ΔVline-reg Vin=2.5V to 6.0V, Iout=0A to 2A -2 2 % Output voltage load regulation ΔVload-reg Vout=0.8V to 3.3V, Iout=0A to 2A -2 2 % Vin rising 2.3 VIN under voltage V UVLO lockout threshold Vin falling 2.1 Feedback current -30 30 nA Ivfb SW leakage current Ileak(sw) Ven=0V, Vin=6V, Vsw=0V or 6V -1 1 µA PMOSFET on resistance Vin=Vgs=5V, Iout=100mA 130 mΩ RdsonP NMOSFET on resistance 100 mΩ RdsonN Vin=Vgs=5V, Iout=100mA PMOSFET current limit IclP 3.2 A Oscillator frequency Fosc 1 MHz Thermal shutdown threshold Ts 150 °C Soft-start time Tss 1 mS Power good threshold Vpg 0.9*Vout Power good current Ipg Vpg=0.3V 3 mA EN high Level input voltage Ven -40°C≤Top≤+85°C 1.3 V EN low level input voltage Ven 0.3 V ■Marking SOP-8 ELM 605DA abc Mark ELM605DA Content Product name a, b, c Assembly lot No.: 000 to 999 repeated 13 - 3 Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter ■Functional description ELM605DA is high-efficiency DC-to-DC step-down converter and capable of delivering up to 2A of output current. It operates in pulse-width modulation at 1MHz fixed frequency with 2.5V to 6V input voltage and provides output voltage ranging from 0.8V to VIN. The high switching frequency allows for the use of smaller external components, and internal synchronous rectifiers improve efficiency and eliminate external Schottky diode. Using the on-resistance of the internal high-side MOSFET to sense switching currents eliminates current-sense resistors, further enhancing the efficiency and reducing the cost. 1. Current mode PWM control Current mode PWM control provides stable switching and cycle-by-cycle current limit for superior load and line response and protection of the internal main switch and synchronous rectifier. ELM605DA switches at 1MHz fixed frequency and regulates the output voltage. The main switch is turned on for a certain period to ramp the inductor current at each rising edge of the internal oscillator under normal operation whereas switched off when the peak inductor current is above the error voltage. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until the next cycle starts. 2. Dropout operation ELM605DA allows the main switch to remain on for more than one switching cycle and increases the duty cycle while the input voltage decreases close to the output voltage. When the duty cycle reaches 100%, the main switch still keeps on in order to deliver the current to the output up to the P MOSFET current limit. The output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. 3. Short Circuit Protection ELM605DA features short circuit protection. When the output is shorted to ground, the oscillator’s frequency is reduced to prevent the inductor’s current from increasing beyond the P-Channel MOSFET current limit. The P-Channel MOSFET current is reduced to lower the short circuit current. The frequency and current limit will return to the normal values once the short circuit condition is removed and the feedback voltage restores above 0.3V. 4. Internal soft-start ELM605DA supports an internal soft-start function, which reduces inrush current and overshoot of the output voltage. Soft-start is achieved by ramping up the reference voltage (Vref), which is applied to the input of the error amplifier. The typical soft-start time is about 1 ms, and it depends on the component’s values on AP circuit. 5. Thermal Shutdown As soon as the junction temperature exceeds the typical 150°C, the device goes into thermal shutdown. In this mode, the P-Channel switch and N-Channel MOSFETs are latched off. 6. Under-voltage lockout The under-voltage lockout circuit prevents mal-operation of the device at low input voltage. It prevents the converter from turning on the switch or MOSFET under undefined conditions. 7. Enable Connect EN to ground forces the device into shutdown mode, whereas to VIN or floating enables the device .Pulling the EN low forces the IC to enter the shutdown mode, in which the P-Channel MOSFET and N-Channel MOSFETs are turned off and the whole device is shut down. If an output voltage is present during shut down, this could be an external voltage source or super cap. The reverse leakage current is specified under electrical parameter table. On the contrary, pulling the EN high starts up the ELM605DA in the way as described soft-start section. 13 - 4 Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter 8. Power good ELM605DA also includes an open-drain power good output that indicates when the regulator output is over 90%of its nominal output. If the output voltage is beyond this range, the power good output is pulled to ground. Since this comparator has no hysteresis on either threshold, a 30μs delay time is added to prevent the power good output from chattering between states. The power good should be pulled to VIN or another supply voltage less than 5.5V through a resistor. ■Application notes 1.Input Capacitor Selection It is necessary for the input capacitor to sustain the ripple current produced during the period of “on” state of the upper MOSFET, so a low ESR is required to minimize the loss. The RMS value of this ripple can be obtained by the following: IinRMS = Iout √ D × ( 1 - D ) where D is the duty cycle, IinRMS is the input RMS current, and Iout is the load current. The equation reaches its maximum value with D = 0.5. The loss of the input capacitor can be calculated by the following equation: Pcin = ESRcin × IinRMS2 where Pcin is the power loss of the input capacitor and ESRcin is the effective series resistance of the input capacitance. Due to large dI/dt through the input capacitor, electrolytic or ceramics should be used. If a tantalum is required, it must be surge-protected. Otherwise, capacitor failure could occur. 2. Output inductor selection The output inductor selection is to meet the requirements of the output voltage ripple and affects the load transient response. The higher inductance can reduce the inductor’s ripple current and induce the lower output ripple voltage. The ripple voltage and current are approximated by the following equations: Vin - Vout Vout ∆I = × ∆Vout = ∆I × ESR Fs × L Vin Although the increase of the inductance reduces the ripple current and voltage, it contributes to the increase of the response time for the regulator to load transient as well. Increasing the switching frequency (Fs) for a given inductor also can reduce the ripple current and voltage but it will increase the switching loss of the power MOS. The way to set a proper inductor value is to have the ripple current (∆I) be approximately 10%~50% of the maximum output current. Once the value has been determined, select an inductor capable of carrying the required peak current without going into saturation. It is also important to have the inductance tolerance specified to keep the accuracy of the system controlled. Using 20% for the inductance (at room temperature) is reasonable tolerance able to be met by most manufacturers. For some types of inductors, especially those with core made of ferrite, the ripple current will increase abruptly when it saturates, which will result in a larger output ripple voltage. 3. Output capacitor selection An output capacitor is required to filter the output and supply the load transient current. The high capacitor value and low ESR will reduce the output ripple and the load transient drop. These requirements are met by a mix of capacitors and careful layout. 13 - 5 Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter In typical switching regulator design, the ESR of the output capacitor bank dominates the transient response. The number of output capacitors can be determined by the following equations: ∆Vesr ESRcap ESRmax = Number of capacitors = ∆Iout ESRmax ∆Vser = change in output voltage due to ESR (assigned by the designer) ∆Iout = load transient ESRcap = maximum ESR per capacitor (specified in manufacturer’s data sheet) ESRmax = maximum allowable ESR High frequency decoupling capacitors should be placed as closely to the power pins of the load as physically possible. For the decoupling requirements, please consult the capacitor manufacturers for confirmation. 4. Output Voltage The output voltage is set using the FB pin and a resistor divider connected to the output as shown in AP Circuit below. The output voltage (Vout) can be calculated according to the voltage of the FB pin (Vfb) and ratio of the feedback resistors by the following equation, where (Vfb) is 0.8V: R2 Vfb = Vout × ( R1 + R2 ) Thus the output voltage is: ( R1 + R2 ) Vout = 0.8 × R2 5. Layout consideration The physical design of the PCB is the final stage in the design of power converter. If designed improperly, the PCB could radiate excessive EMI and contribute instability to the power converter. Therefore, follow the PCB layout guidelines below can ensure better performance of ELM605DA. (1). The bold lines of AP Circuit below show the main power current paths. Keep the traces short and wide. (2). To reduce resistive voltage drops and the number of via, ELM605DA and power components (Cin1, Cin2, Cout and L) should be placed on the component side of the board and power current traces routed on its component layer. (3). SW node supports high frequency voltage swing (dv/dt). It should be routed small area. (4). Place input capacitor CIN as close as possible to the IC pins (VIN and PGND). (5). To avoid the switching noise from polluting the ELM605DA’s internal circuit, place a resistor between the VIN and VCC pin. A bypass capacitor C8 (0.1µF) should be placed between analog ground pin (GND) and VCC pin. (6). Place feedback components (R1, R2 and C5 ) behind the output capacitor and near the ELM605DA. Keep the feedback loop area small and away from SW node. (7). To avoid PGND terminal is polluting the ELM605DA’s internal ground. The analog ground pin (GND) should be connected to a clearer node as show in AP circuit below. (8). To minimize parasitical capacitor couplings and magnetic field-to-loop couplings, the power converter should be located away from other circuitry, especially from sensitive analog circuitry. 13 - 6 Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter ELM605DA AP Circuit AP circuit Short and wide traces R4 ELM605DA CIN C8 VIN VCC 1 L R6 VOUT VIN 8 2 PG 3 GND SW 7 PGND 6 VOUT Cout R1 PGND 4 EN FB 5 C5 EN SOP-8 TOP VIEW R2 ■Evaluation circuit C1=10µF, C2=0.1µF, C3=22µF, C5=1nF, C7= NC, C8=0.1µF, R3=100KΩ, R4=10, R6=100K, L=2.2µH Vout=3.3V Vout=1.8V Vout=1.2V Vout=1.0V R1 47K R2 15K 12.5K 5K 10K 10K 24K 6K R4 10 Ω C8 0.1µF U1 1 2 3 4 R6 Vout VCC VIN PG SW 7 6 GND PGND 5 EN EN FB R3 Vin 8 ELM605DA 100K Ω PG C2 0.1µF 100KΩ EN C7 NC 13 - 7 Vin C1 10µF L=2.2µH 2 1 Vout=0.8~(R1+R2)/R2 Vout C3 22µF R1 C5 1nF R2 Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter ■Typical characteristics • Vin=3.3V, Vout=1.0V • Vin=3.3V, Vout=1.0V, R1=6K, R2=24K, Top=25°C Vout-Iout 1.15 90.0 1.1 80.0 1.05 1 0.95 0.9 70.0 60.0 50.0 40.0 30.0 20.0 0.85 10.0 0.8 0.1 1000 100 10 1 Iout (mA) Vout-Vin 1.2 0.0 0.1 10000 1 10 100 Iout (mA) 1000 10000 Vout=1.0V Iout=10mA 1.1 Vout (V) Vin=3.3V, Vout=1.0V 100.0 Efficiency (%) Vout (V) Efficiency-Iout Vin=3.3V, Vout=1.0V 1.2 1 0.9 Iout=100mA Iout=1A 0.8 0.7 1 2 3 4 Vin (V) 5 6 7 13 - 8 Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter • Vin=3.3V, Vout=1.8V • Vin=3.3V, Vout=1.8V, R1=12.5K, R2=10K, Top=25°C Vout-Iout 2.1 90.0 2 80.0 1.9 1.8 1.7 1.6 70.0 60.0 50.0 40.0 30.0 20.0 1.5 10.0 1.4 0.1 10 1 1000 100 Iout (mA) Vout-Vin 1.9 0.0 0.1 10000 1 10 100 Iout (mA) 1000 10000 Vout=1.8V 2 Vout (V) Vin=3.3V, Vout=1.8V 100.0 Efficiency (%) Vout (V) Efficiency-Iout Vin=3.3V, Vout=1.8V 2.2 Iout=10mA 1.8 1.7 Iout=1A 1.6 Iout=100mA 1.5 0 1 2 3 4 Vin (V) 5 6 7 13 - 9 Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter • Vin=5.0V, Vout=1.2V • Vin=5.0V, Vout=1.2V, R1=5K, R2=10K, Top=25°C Vout-Iout Efficiency-Iout Vin=5V, Vout=1.2V 1.5 1.45 90.0 1.4 80.0 Efficiency (%) 1.35 Vout (V) Vin=5V, Vout=1.2V 100.0 1.3 1.25 1.2 1.15 70.0 60.0 50.0 40.0 30.0 1.1 20.0 1.05 10.0 1 0.1 10 1 1000 100 Iout (mA) 0.0 0.1 10000 1 10 100 Iout (mA) 1000 10000 Vout-Vin Vin=5V, Vout=1.2V 1.4 Vout (V) 1.3 Iout=10mA 1.2 1.1 Iout=1A 1 0.9 Iout=100mA 0 1 2 3 4 Vin (V) 5 6 7 13 - 10 Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter • Vin=5V, Vout=3.3V • Vin=5.0V, Vout=3.3V, R1=47K, R2=15K, Top=25°C Vout-Iout 3.5 3.45 90.0 3.4 80.0 3.35 70.0 3.3 3.25 3.2 3.15 60.0 50.0 40.0 30.0 3.1 20.0 3.05 10.0 3 0.1 10 1 1000 100 Iout (mA) Vout-Vin Vout (V) 0.0 0.1 10000 1 10 100 Iout (mA) 1000 10000 Vout=3.3V 3.5 3.4 Vin=5V, Vout=3.3V 100.0 Efficiency (%) Vout (V) Efficiency-Iout Vin=5V, Vout=3.3V Iout=10mA 3.3 3.2 Iout=100mA 3.1 3 0 1 2 Iout=1A 3 4 Vin (V) 5 6 7 13 - 11 Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter ■Dynamic load waveform ■Vin,Vout woveform Dynamic Dynamic load load waveform waveform Steady Steady state state waveform waveform Iout=1A, Iout=1A,Vout=3.3V Vout=3.3V Vout Vout(AC) (AC) 100mV/Div 100mV/Div Vin=5V,Vout=3.3V, Vin=5V,Vout=3.3V,Iout=1A Iout=1A Dynamic load waveform Vin Vin(AC) (AC) 100mV/Div 100mV/Div Iout=1A, Vout=3.3V Steady state waveform Vin=5V,Vout=3.3V, Iout=1A Vin (AC) 100mV/Div Vout (AC) 100mV/Div Vout Vout(AC) (AC) 10mV/Div 10mV/Div Iout Iout '0.5A/Div '0.5A/Div Iout '0.5A/Div Vout (AC) 10mV/Div Time Time (500µs/Div) (500µs/Div) Time Time (1.0µs/Div) (1.0µs/Div) Time (500µs/Div) Time (1.0µs/Div) Power Power on/off on/off from from EN EN ■Power ON/OFF from EN Vin=5V, Vin=5V,Vout=3.3V, Vout=3.3V,Iout=40mA Iout=40mA Ven Ven 2V/Div 2V/Div Power Power on/off on/off from from EN EN Vin=5V, Vin=5V,Vout=3.3V, Vout=3.3V,Iout=1A Iout=1A Power on/off from EN Ven Ven 2V/Div 2V/Div Vin=5V, Vout=3.3V, Iout=40mA Ven 2V/Div Vout Vout 2V/Div 2V/Div Ven 2V/Div Vout Vout 2V/Div 2V/Div Vout Iout Iout 2V/Div 20mA/Div 20mA/Div Vout Iout Iout 2V/Div 1A/Div 1A/Div Iout 20mA/Div Time Time (1ms/Div) (1ms/Div) Iout 1A/Div Time (1ms/Div) Power on/off from EN Vin=5V, Vout=3.3V, Iout=1A Time Time (1ms/Div) (1ms/Div) Time (1ms/Div) 13 - 12 Rev.1.2 ELM605DA 2A synchronous step-down DC/DC converter ■Fosc-Top ■Vfb-Top ■Switching temperature characteristics ■Fosc-Top ■Fosc-Top ■Vfb-Top ■Vfb-Top Vfb-Top Vin=5V, Vout=3.3V 0.82 Vfb-Top Vfb-Top Vin=5V, Vin=5V, Vout=3.3V Vout=3.3V 0.82 0.82 Vin=5V, Vout=3.3V Fosc-Top Fosc-Top Vin=5V, Vin=5V, Vout=3.3V Vout=3.3V 1050.0 1050.0 1000.0 0.81 Fosc (KHz) Fosc (KHz) Fosc (KHz) 1000.0 1000.0 950.0 Vfb (V) Vfb (V) Vfb (V) 0.81 0.81 0.8 950.0 950.0 900.0 0.80.8 0.79 900.0 900.0 850.0 0.79 0.79 0.78 -40 -20 Fosc-Top 1050.0 0 20 40 60 Top (°C) 850.0 850.0 800.0 -40 -20 80 100 120 0 20 40 60 Top (°C) 80 100 120 800.0 800.0 120120 -40-40-20-20 0 0 20 2040 4060 6080 80100100 0.78 0.78 -40-40-20-20 0 0 20 2040 4060 6080 80100100 120120 Top Top (°C) (°C) Top Top (°C) (°C) ■Iq-Top ■Iq-Top ■Iq-Top Iq-Top 240 Vin=5V Iq-Top Iq-Top 240240 230 Vin=5V Vin=5V Iq (�A) Iq (�A) Iq (�A) 230230 220 220220 210 210210 200 200200 190 -40 -20 0 20 40 60 Top (°C) 80 100 120 190190 120120 -40-40-20-20 0 0 20 2040 4060 6080 80100100 Top Top (°C) (°C) 13 - 13 Rev.1.2