® RT2657 2.25MHz 600mA Synchronous Step-Down Converter General Description Features The RT2657 is a high efficiency Pulse-Width-Modulated (PWM) step-down DC/DC converter, capable of delivering 600mA output current over a wide input voltage range from 2.7V to 5.5V. The RT2657 is ideally suited for portable electronic devices that are powered from 1-cell Li-ion battery or from other power sources such as cellular phones, PDAs, hand-held devices, game console and related accessories. VIN Range 2.7V to 5.5V VOUT Range 0.6V to 5.5V (100% Duty Ratio Operation) VREF = 0.6V ISD ≤ 5μ μA (VEN = 0V) Current Mode Control, Internal Compensation Fixed FSW 2.25MHz R DS(ON) 230mΩ Ω HS/250mΩ Ω LS (P-MOSFET/ N-MOSFET) Enable (VIH = 1V, VIL = 0.4V); Int. Soft-Start (0.3ms) Up to 600mA Output Current Up to 90% Efficiency Peak ILIMIT (1.5A Typical / 0.8A Min); UVLO; UVP; VIN and VOUT OVP; and OTP (150°°C) No Schottky Diode Required Internal Compensation to Reduce External Components RoHS Compliant and Halogen Free The internal synchronous rectifier with low R DS(ON) dramatically reduces conduction loss at PWM mode. No external Schottky diode is required in practical applications. The RT2657 enters Low Dropout Mode when normal Pulse -Width Mode cannot provide regulated output voltage by continuously turning on the upper P-MOSFET. The RT2657 enters shut-down mode and consumes less than 5μA when the EN pin is pulled low. The switching ripple is easily smoothed-out by small package filtering elements due to a fixed operating frequency of 2.25MHz. Applications The RT2657 is available in the small WDFN-6SL 2x2 package. Marking Information 1WW 1W : Product Code W : Date Code Portable Instruments Game Console and Accessories Microprocessors and DSP Core Supplies Cellular Phones Wireless and DSL Modems PC Cards Automotive InfoTainMent Simplified Application Circuit RT2657 VIN L1 LX VIN CIN EN Copyright © 2013 Richtek Technology Corporation. All rights reserved. November 2013 R1 COUT FB GND DS2657-00 VOUT C1 R2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT2657 Pin Configurations Ordering Information (2) (TOP VIEW) Taping Type ( Pin1 at Q2) Package Type QW : WDFN-6SL 2x2 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) LX 1 NC FB 2 GND RT2657 3 7 6 GND 5 VIN EN 4 WDFN-6SL 2x2 Note : Richtek products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Function Pin Description Pin No. Pin Name Pin Function 1 LX Switch Node. Connect to the external inductor. 2 NC No Internal Connection. Connect to GND. 3 FB Feedback Voltage Input. Connect to the external resistor divider. 4 EN Enable Control Input (Active High). 5 VIN Power Input. Connect to the input capacitor. 6, GND 7 (Exposed Pad) Power GND. The Exposed Pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Function Block Diagram EN OSC & Shutdown Control Slope Compensation VIN RS1 Current Limit Detector Current Sense FB Error Amplifier RC Control Logic Driver LX PWM Comparator RS2 COMP UVLO & Power Good Detector Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 GND VREF is a registered trademark of Richtek Technology Corporation. DS2657-00 November 2013 RT2657 Operation The RT2657 is a synchronous low voltage Buck Converter that can support the input voltage range from 2.7V to 5.5V and the output current can be up to 0.6A. The RT2657 uses a constant frequency, current mode architecture. In normal operation, the high-side P-MOSFET is turned on when the Switch Controller is set by the oscillator (OSC) and is turned off when the current comparator resets the Switch Controller. The high-side MOSFET peak current is measured by internal R SENSE. The current signal is where Slope Compensator works together with sensing voltage of RSENSE. The error amplifier EA adjusts COMP voltage by comparing the feedback signal (VFB) from the output voltage with the internal 0.6V reference. When the load current increases, it causes a drop in the feedback voltage relative to the reference. The COMP voltage then rises to allow higher inductor current to match the load current. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS2657-00 November 2013 UV Comparator If the feedback voltage (VFB) is lower than threshold voltage 0.2V, the UV Comparator's output will go high and the Switch Controller will turn off the high-side MOSFET. Oscillator (OSC) The internal oscillator runs at 2.25MHz. Enable Comparator The EN pin can be connected to VIN through a 100kΩ resistor for automatic startup. Soft-Start (SS) An internal current source (25nA) charges an internal capacitor (15pF) to build the soft-start ramp voltage (VSS). The VFB voltage will track the internal ramp voltage during soft-start interval. The typical soft-start time is 300μs. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT2657 Absolute Maximum Ratings (Note 1) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------Switch Voltage, LX ------------------------------------------------------------------------------------------------All Other Pins ------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WDFN-6SL 2x2 ----------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WDFN-6SL 2x2, θJA -----------------------------------------------------------------------------------------------WDFN-6SL 2x2, θJC ----------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) --------------------------------------------------------------------------------------- Recommended Operating Conditions −0.3V to 6.5V −0.3V to (VIN + 0.3V) −0.3V to 6V 0.833W 120°C/W 12°C/W 260°C 150°C −65°C to 150°C 2kV (Note 4) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------- 2.7V to 5.5V Junction Temperature Range ------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 3.6V, TA = −40°C to 85°C unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Output Current IOUT VIN = 2.7V to 5.5V -- -- 0.6 A Quiescent Current IQ VEN = 1V, VFB = 0.5V -- 300 -- A Feedback Voltage VFB VIN = 2.7V to 5.5V @ T A = 25C 588 600 612 VIN = 2.7V to 5.5V 585 600 615 VIN Rising 1.85 2.2 2.55 V Hysteresis -- 0.2 -- V VEN = 0V -- -- 5 A -- 2.25 -- MHz Under-Voltage Lockout Threshold VUVLO Shutdown Current ISHDN Switching Frequency EN Input Voltage Logic-High VIH 1 -- VIN V Logic-Low VIL -- -- 0.4 V T SD -- 150 -- °C High-Side RDS(ON)_H ISW = 0.2A -- 230 -- m Low-Side RDS(ON)_L ISW = 0.2A -- 250 -- m 0.8 1.5 -- A -- 1 -- % Thermal Shutdown Temperature Switch On-Resistance Peak Current Limit Output Voltage Load Regulation ILIM 0mA < IOUT < 0.6A Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 mV is a registered trademark of Richtek Technology Corporation. DS2657-00 November 2013 RT2657 Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS2657-00 November 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT2657 Typical Application Circuit RT2657 5 VIN CIN 4.7µF VIN 4 EN 6, 7 (Exposed Pad) GND L1 2.2µH VOUT 2.3V C1 10pF FB Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 LX 1 3 R1 680k COUT 10µF R2 240k is a registered trademark of Richtek Technology Corporation. DS2657-00 November 2013 RT2657 Typical Operating Characteristics Efficiency vs. Output Current 100 Output Voltage vs. Input Voltage 2.00 VIN = 3.3V 90 1.95 VIN = 5V 1.90 Output Voltage (V) Efficiency (%) 80 70 60 50 40 30 1.85 1.80 1.75 1.70 20 1.65 10 VOUT = 1.8V, IOUT = 0A VOUT = 1.8V 0 1.60 0 0.1 0.2 0.3 0.4 0.5 0.6 2.5 3 3.5 Output Current (A) Frequency vs. Input Voltage 5 5.5 Frequency vs. Temperature 2.40 2.35 2.4 VOUT = 1.2V Frequency (MHz)1 VOUT = 1.2V 2.3 VOUT = 1.8V 2.2 2.1 2.0 1.9 2.30 VOUT = 1.8V 2.25 2.20 2.15 2.10 2.05 VIN = 5V, IOUT = 0.3A IOUT = 0.3A 1.8 2.00 2.5 3 3.5 4 4.5 5 5.5 -50 -25 Input Voltage (V) 25 50 75 100 125 Output Current Limit vs. Temperature 1.8 2.5 1.7 Output Current Limit (A) 3.0 2.0 0 Temperature (°C) Output Current Limit vs. Input Voltage Output Current Limit (A) 4.5 Input Voltage (V) 2.5 Frequency (MHz)1 4 VOUT = 1.2V 1.5 VOUT = 1.8V 1.0 0.5 1.6 1.5 1.4 1.3 VIN = 5V, VOUT = 1.2V 0.0 1.2 2.5 3 3.5 4 4.5 5 Input Voltage (V) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS2657-00 November 2013 5.5 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT2657 VFB vs. Temperature 0.66 1.84 0.65 1.83 0.64 1.82 0.63 1.81 0.62 VFB (V) Output Voltage (V) Output Voltage vs. Temperature 1.85 1.80 1.79 0.61 0.60 1.78 0.59 1.77 0.58 1.76 VIN = 5V, VOUT = 1.8V, IOUT = 0.3A 1.75 0.57 VIN = 3.3V, VOUT = 0.6V 0.56 -50 -25 0 25 50 75 100 125 -50 25 50 75 Temperature (°C) Output Ripple Output Ripple VOUT (10mV/Div) VLX (2V/Div) VLX (5V/Div) VIN = 5V, VOUT = 1.2V, IOUT = 0.6A 100 125 VIN = 5V, VOUT = 1.8V, IOUT = 0.6A Time (250ns/Div) Time (250ns/Div) Load Transient Response Load Transient Response VOUT (50mV/Div) VOUT (50mV/Div) VIN = 5V, VOUT = 1.8V, IOUT = 0A to 0.6A Time (100μs/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 0 Temperature (°C) VOUT (10mV/Div) IOUT (500mA/Div) -25 IOUT (500mA/Div) VIN = 5V, VOUT = 1.8V, IOUT = 0.2A to 0.6A Time (100μs/Div) is a registered trademark of Richtek Technology Corporation. DS2657-00 November 2013 RT2657 Power On from EN Power Off from EN VEN (2V/Div) VEN (2V/Div) VOUT (1V/Div) VOUT (1V/Div) IOUT (500mA/Div) IOUT (500mA/Div) VIN = 5V, VOUT = 1.8V, IOUT = 0.6A VIN = 5V, VOUT = 1.8V, IOUT = 0.6A Time (100μs/Div) Time (100μs/Div) UVLO vs. Temperature EN Threshold vs. Temperature 2.8 1.00 0.95 2.6 EN Threshold (V) 0.90 UVLO (V) 2.4 Rising 2.2 2.0 Falling 0.80 Rising 0.75 0.70 0.65 0.60 1.8 VOUT = 1.2V 1.6 Falling 0.55 VIN = 5V, VOUT = 1.2V 0.50 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS2657-00 0.85 November 2013 125 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT2657 Application Information The basic RT2657 application circuit is shown in Typical Application Circuit. External component selection is determined by the maximum load current and begins with the selection of the inductor value and operating frequency followed by CIN and COUT. Output Voltage Setting The output voltage is set by an external resistive divider according to the following equation : R1 VOUT VREF x (1 ) R2 where VREF equals to 0.6V typically. The resistive divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 1. VOUT R1 The RT2657 is designed to operate down to an input supply voltage of 2.7V. One important consideration at low input supply voltages is that the RDS(ON) of the P-Channel and N-Channel power switches increases. Users should calculate the power dissipation when the RT2657 is used at 100% duty cycle with low input voltages to ensure that thermal limits are not exceeded. Under-Voltage Protection (UVP) The output voltage is continuously monitored for undervoltage protection. When the output voltage is less than 33% of its set voltage threshold after OCP occurs, the under-voltage protection circuit will be triggered to auto re-softstart. Input Over-Voltage protection (VIN OVP) FB RT2657 Low Supply Operation When the input voltage (VIN) is higher than 6V, VIN OVP will be triggered and the IC stops switching. Once the input voltage drops below 6V, the IC will return to normal operation. R2 GND Figure 1. Setting the Output Voltage Output Over-Voltage Protection (VOUT OVP) Soft-Start The RT2657 contains an internal soft-start clamp that gradually raises the clamp on the FB pin. Time from active EN to reach 95% of VOUT nominal is within typical 300μs. 100% Duty Cycle Operation When the input supply voltage decreases toward the output voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage forces the main switch to remain on for more than one cycle, eventually reaching 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across the internal P-MOSFET and the inductor. When the output voltage exceeds more than 5% of the nominal reference voltage, the feedback loop forces the internal switches off within 50μs. Therefore, the output over-voltage protection is automatically triggered by the loop. Short Circuit Protection When the output is shorted to ground, the inductor current decays very slowly during a single switching cycle. A current runaway detector is used to monitor inductor current. As current increases beyond the control of current loop, switching cycles will be skipped to prevent current runaway from occurring. Table 1. Inductors Component Supplier Series TAIYO YUDEN NR5018 T2R2M Inductance (H) 2.2H Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 DCR (m) 40 Current Rating (mA) Dimensions (mm) 3000 4 X 4 X 1.8 is a registered trademark of Richtek Technology Corporation. DS2657-00 November 2013 RT2657 CIN and COUT Selection The input capacitance, C IN, is needed to filter the trapezoidal current at the Source of the high-side MOSFET. To prevent large ripple voltage, a low ESR input capacitor sized for the maximum RMS current should be used. RMS current is given by : IRMS IOUT(MAX) VOUT VIN VIN 1 VOUT This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT/2. This simple worst case condition is commonly used for design because even significant deviations do not result in much difference. Choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. The selection of COUT is determined by the effective series resistance (ESR) that is required to minimize voltage ripple and load step transients, as well as the amount of bulk capacitance that is necessary to ensure the control loop is stable. Loop stability can be checked by viewing the load transient response. The output ripple, ΔVOUT, is determined by : 1 VOUT IL ESR 8fCOUT The output ripple is highest at maximum input voltage since ΔIL increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirements. Dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are all available in surface mount packages. Special polymer capacitors offer very low ESR, but have lower capacitance density than other types. Tantalum capacitors have the highest capacitance density, but it is important to only use types that have been surge tested for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR, but can be used in cost-sensitive applications provided that consideration is given to ripple current ratings and long term reliability. Ceramic capacitors have excellent low ESR characteristics, but can have a high voltage coefficient and audible piezoelectric effects. The high Q of ceramic capacitors with trace inductance can also lead to significant ringing. Using Ceramic Input and Output Capacitors Higher value, 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. However, care must be taken when these capacitors are used at the input and output. When a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, VIN. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part. Table 2. Capacitors for CIN and COUT Component Supplier Part No. Capacitance (F) Case Size MuRata GRM31CR71A475KA01 4.7F 1206 MuRata GRM31CR71A106KA01 10F 1206 Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS2657-00 November 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT2657 Thermal Considerations Layout Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : Follow the PCB layout guidelines for optimal performance of the RT2657. LX node experiences high frequency voltage swing and should be kept within a small area. Keep all sensitive small-signal nodes away from the LX node to prevent stray capacitive noise pick up. PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications of the RT2657, the maximum junction temperature is 125°C and TA is the ambient temperature. The junction to ambient thermal resistance, θ JA , is layout dependent. For WDFN-6SL 2x2 packages, the thermal resistance, θJA, is 120°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : PD(MAX) = (125°C − 25°C) / (120°C/W) = 0.833W for WDFN-6SL 2x2 package Connect the terminal of the input capacitor(s), CIN, as close as possible to the VIN pin. This capacitor provides the AC current into the internal power MOSFETs. Flood all unused areas on all layers with copper. Flooding with copper will reduce the temperature rise of power components. Connect the copper areas to any DC net (VIN, VOUT, GND, or any other DC rail in the system). Connect the FB pin directly to the feedback resistors. The resistive voltage divider must be connected between VOUT and GND. LX should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. COUT VOUT VOUT LX 1 NC C1 FB 2 GND L1 The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. 3 7 R1 R2 6 GND 5 VIN EN 4 CIN Input capacitor must be placed as close to the IC as possible. Maximum Power Dissipation (W)1 1.0 Figure 3. PCB Layout Guide Four-Layer PCB 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 2. Derating Curve of Maximum Power Dissipation Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS2657-00 November 2013 RT2657 Outline Dimension D2 D L E E2 1 SEE DETAIL A 2 e 2 1 b A A1 1 DETAIL A Pin #1 ID and Tie Bar Mark Options A3 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.200 0.350 0.008 0.014 D 1.900 2.100 0.075 0.083 D2 1.550 1.650 0.061 0.065 E 1.900 2.100 0.075 0.083 E2 0.950 1.050 0.037 0.041 e L 0.650 0.200 0.026 0.300 0.008 0.012 W-Type 6SL DFN 2x2 Package Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements 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 Richtek or its subsidiaries. DS2657-00 November 2013 www.richtek.com 13