RT8057 2.25MHz 1A Synchronous Step-Down Converter General Description Features The RT8057 is a high efficiency Pulse-Width-Modulated (PWM) step-down DC/DC converter, capable of delivering 1A output current over a wide input voltage range from 2.7V to 5.5V. The RT8057 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, handheld devices, game console and related accessories. z 2.7V to 5.5V Wide Input Operation Range z 2.25MHz Fixed-Frequency PWM Operation Up to 1A Output Current Up to 90% Efficiency 0.6V Reference Allows Low Output Voltage Internal Soft-Start No Schottky Diode Required Internal Compensation to Reduce External Components Low Dropout Operation : 100% Duty Cycle 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 RT8057 enters Low Dropout Mode when normal Pulse -Width Mode cannot provide regulated output voltage by continuously turning on the upper P-MOSFET. The RT8057 enters shut-down mode and consumes less than 1μA 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. z z z z z z z z Applications z z z z z The RT8057 is available in a small WDFN-6SL 2x2 package. Ordering Information RT8057 z Portable Instruments Game Console and Accessories Microprocessors and DSP Core Supplies Cellular Phones Wireless and DSL Modems PC Cards Pin Configurations (2) (TOP VIEW) Package Type QW : WDFN-6SL 2x2 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : ` ` 1 2 3 7 6 GND 5 VIN EN 4 WDFN-6SL 2x2 Marking Information J7 : Product Code RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. LX NC FB GND Taping Type ( Pin1 at Q2) J7W W : Date Code Suitable for use in SnPb or Pb-free soldering processes. DS8057-03 November 2011 www.richtek.com 1 RT8057 Typical Application Circuit RT8057 5 VIN CIN 4.7µF LX VIN 1 L1 2.2µH VOUT 2.3V 4 EN 6, 7 (Exposed Pad) C1 10pF FB 3 R1 680k COUT 10µF R2 240k GND 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 Pin. Connect to the external resistor divider. 4 EN Chip Enable (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 www.richtek.com 2 UVLO & Power Good Detector GND VREF DS8057-03 November 2011 RT8057 Absolute Maximum Ratings z z z z z z z (Note 1) Supply Input Voltage, VIN -----------------------------------------------------------------------------------------------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 -------------------------------------------------------------------------------------------------------------------------MM ---------------------------------------------------------------------------------------------------------------------------- Recommended Operating Conditions z z z 6.5V 0.606W 165°C/W 8.2°C/W 260°C 150°C −65°C to 150°C 2kV 200V (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 = 25°C unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Output Current IOUT VIN = 2.7V to 5.5V -- -- 1 A Quiescent Current IQ IOUT = 0mA -- 81 -- μA Reference Voltage VREF −2 -- 2 −2.5 -- 2.5 VIN Rising 2 2.2 2.4 V Hysteresis -- 0.2 -- V -- 0.1 1 μA -- 2.25 -- MHz Under Voltage Lockout Threshold VUVLO Shutdown Current Note 5 ISHDN Switching Frequency % EN Threshold Logic-High Voltage Logic-Low VIH 1 -- VIN V VIL -- -- 0.4 V Thermal Shutdown Temperature TSD -- 150 -- °C High Side RDS(ON)_H ISW = 0.2A -- 250 -- mΩ Low Side RDS(ON)_L ISW = 0.2A -- 200 -- mΩ 1.1 1.5 2 A Switch On Resistance Peak Current Limit ILIM Output Voltage Line Regulation VIN = 2.7V to 5.5V -- -- 1 %/V Output Voltage Load Regulation 0mA < IOUT < 0.6A -- -- 1 % 200 300 400 μs Start-Up Time DS8057-03 November 2011 tss Guaranteed by Design www.richtek.com 3 RT8057 Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to affect device reliability. Note 2. θJA is measured in natural convection at TA = 25°C on a low-effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard. The measurement case position of θJC is on the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. The reference voltage accuracy is ±2.5% at recommended ambient temperature range, guaranteed by design. www.richtek.com 4 DS8057-03 November 2011 RT8057 Typical Operating Characteristics Output Voltage vs. Input Voltage Efficiency vs. Output Current 2.38 100 VIN = 5V 90 2.36 VIN = 3.3V Output Voltage (V) Efficiency (%) 80 70 60 50 40 30 2.34 2.32 2.30 2.28 2.26 20 2.24 10 VOUT = 2.3V, IOUT = 0A VOUT = 2.3V 0 2.22 0.0 0.2 0.4 0.6 0.8 1.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 Input Voltage (V) Output Current (A) Frequency vs. Input Voltage Frequency vs. Temperature 2.40 2.30 2.35 2.25 2.30 2.20 Frequency (MHz)1 Frequency (MHz)1 VIN = 3.3V 2.25 2.20 2.15 2.10 2.05 VIN = 5V 2.15 2.10 2.05 2.00 1.95 VIN = 5V, VOUT = 2.3V, IOUT = 0.2A VOUT = 2.3V, IOUT = 0.2A 1.90 2.00 2.5 3.0 3.5 4.0 4.5 5.0 -50 5.5 -25 0 Output Current Limit vs. Input Voltage 50 75 100 125 Output Current Limit vs. Temperature 1.6 1.6 1.5 1.5 Output Current Limit (A) Output Current limit (A) 25 Temperature (°C) Input Voltage (V) 1.4 1.3 1.2 1.1 1.4 1.3 1.2 1.1 VOUT = 2.3V VIN = 5V, VOUT = 2.3V 1.0 1.0 2.5 3.0 3.5 4.0 4.5 Input Voltage (V) DS8057-03 November 2011 5.0 5.5 -50 -25 0 25 50 75 100 125 Temperature (°C) www.richtek.com 5 RT8057 Reference Voltage vs. Temperature Output Voltage vs. Temperature 0.608 2.34 0.606 Reference Voltage (V) 2.35 Output Voltage (V) 2.33 2.32 2.31 2.30 2.29 2.28 2.27 VIN = 5V, VOUT = 2.3V, IOUT = 0A 2.26 0.604 0.602 0.600 0.598 0.596 0.594 VIN = 5V, VOUT = 2.3V 0.592 2.25 -50 -25 0 25 50 75 100 125 -50 25 50 75 100 125 Output Ripple Output Ripple VLX (5V/Div) VOUT (5mV/Div) VOUT (5mV/Div) VIN = 3.3V, VOUT = 2.3V, IOUT = 1A VIN = 5V, VOUT = 2.3V, IOUT = 1A Time (250ns/Div) Time (250ns/Div) Load Transient Response Load Transient Response VOUT (100mV/Div) VOUT (100mV/Div) IOUT (500mA/Div) IOUT (500mA/Div) VIN = 5V, VOUT = 2.3V, IOUT = 0A to 1A Time (100μs/Div) www.richtek.com 6 0 Temperature (°C) Temperature (°C) VLX (5V/Div) -25 VIN = 5V, VOUT = 2.3V, IOUT = 0.4A to 1A Time (100μs/Div) DS8057-03 November 2011 RT8057 Power On from EN Power Off from EN VIN = 5V, VOUT = 2.3V, IOUT = 1A VEN (2V/Div) VEN (2V/Div) VOUT (2V/Div) VOUT (2V/Div) IOUT (500mA/Div) VIN = 5V, VOUT = 2.3V, IOUT = 1A IOUT (500mA/Div) Time (100μs/Div) Time (100μs/Div) UVLO vs. Temperature En Threshold vs. Temperature 0.80 2.4 2.3 0.78 Turn On EN Threshold (V) UVLO (V) Turn On 0.76 2.2 2.1 Turn Off 2.0 1.9 1.8 1.7 0.74 0.72 0.70 0.68 0.66 Turn Off 0.64 1.6 0.62 VIN = 5V, VOUT = 2.3V VOUT = 2.3V 0.60 1.5 -50 -25 0 25 50 75 100 125 -50 -25 0 25 50 75 100 125 Temperature (°C) Temperature (°C) Output Voltage vs. Output Current 2.34 Output Voltage (V) 2.33 2.32 2.31 2.30 2.29 2.28 2.27 VIN = 5V, VOUT = 2.3V 2.26 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Output Current (A) DS8057-03 November 2011 www.richtek.com 7 RT8057 Application Information The basic RT8057 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 typical. The resistive divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 1. VOUT The RT8057 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. The user should calculate the power dissipation when the RT8057 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 can be continuously monitored for under voltage 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 Voltage Over Voltage protection (VIN OVP) R1 FB RT8057 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 RT8057 contains an internal soft-start clamp that gradually raises the clamp on the FB pin. 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 TAIYO YUDEN www.richtek.com 8 Series NR 4018 T2R2M Inductance (µH) 2.2µH DCR (mΩ) 60 Current Rating (mA) 2700 Dimensions (mm) 4 X 4 X 1.8 DS8057-03 November 2011 RT8057 CIN and COUT Selection The input capacitance, CIN, is needed to filter the trapezoidal current at the source of the top 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 : V IRMS = IOUT(MAX) OUT 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 that the control loop is stable. Loop stability can be checked by viewing the load transient response. The output ripple, ∆VOUT , is determined by : 1 ∆VOUT ≤ ∆IL ESR + 8fCOUT The output ripple is highest at maximum input voltage since ∆IL 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 of 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 (µF) Case Size MuRata GRM31CR71A475KA01 4.7µF 1206 MuRata GRM31CR71A106KA01 10µF 1206 DS8057-03 November 2011 www.richtek.com 9 RT8057 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 RT8057. } } 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 RT8057, 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 165°C/W on a standard JEDEC 51-3 single-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) / (165°C/W) = 0.606W 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. For the RT8057 package, 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 Figure 3. PCB Layout Guide 0.65 Single-Layer PCB 0.60 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0 25 50 75 100 125 Ambient Temperature (°C) Figure 2. Derating Curve for the RT8057 Package www.richtek.com 10 DS8057-03 November 2011 RT8057 Outline Dimension D2 D L E E2 1 e 2 b A A1 SEE DETAIL A 1 2 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. Dimensions In Millimeters Dimensions In Inches Symbol 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 Richtek Technology Corporation Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 5F, No. 95, Minchiuan Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)86672399 Fax: (8862)86672377 Email: [email protected] Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek. DS8057-03 November 2011 www.richtek.com 11