RT8060A 1.5MHz, 1A High Efficiency Step-Down Converter General Description Features The RT8060A is a current mode, high efficiency PWM step-down DC/DC converter that can support a wide input voltage range from 2.7V to 5.5V, while delivering up to 1A output current. The current mode operation provides fast transient response and eases loop stabilization. z A 1.5MHz frequency operation allows the use of a smaller inductor to meet the space and height limitations handheld applications. z z z z z z z z The RT8060A is available in a SOT-23-5 package. z z 2.7V to 5.5V Wide Input Voltage Range Adjustable Output Voltage 1A Output Current Up to 95% Efficiency 1.5MHz Fixed Frequency PWM Operation Power Good Indicator Over Current Protection Internal Sort-Start No Schottky Diode Required Internal Compensation RoHS Compliant and Halogen Free Ordering Information RT8060A Applications Package Type B : SOT-23-5 z z Lead Plating System G : Green (Halogen Free and Pb Free) Storage Device : HDD/ODD Wireless and DSL Modems Pin Configurations Note : (TOP VIEW) Richtek products are : ` RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` FB VIN 5 4 Suitable for use in SnPb or Pb-free soldering processes. 2 PGOOD GND LX Marking Information 20 = : Product Code 20=DNN 3 SOT-23-5 DNN : Date Code Typical Application Circuit 4 VIN CIN 4.7µF VIN LX RT8060A 5 FB 1 PGOOD GND DS8060A-00 March 2011 3 L 2.2µH VOUT R1 200k C1 10pF COUT 10µF R2 200k 2 www.richtek.com 1 RT8060A Functional Pin Description Pin No. Pin Name Pin Function 1 PGOOD Power Good Indicator. 2 GND Ground. 3 LX Switch Node. 4 VIN Supply Input. 5 FB Feedback Input. Function Block Diagram VIN OSC & Shutdown Control Slope Compensation Current Sense Control Logic PWM Comparator FB RS1 Current Limit Detector Driver LX Error Amplifier RC CCOMP UVLO & Power Good Detector RS2 GND VREF PGOOD www.richtek.com 2 DS8060A-00 March 2011 RT8060A Absolute Maximum Ratings z z z z z z z z z (Note 1) Supply Input Voltage, VIN -----------------------------------------------------------------------------------------LX Pin Voltage -------------------------------------------------------------------------------------------------------Other I/O Pin Voltage ----------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C SOT-23-5 -------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SOT-23-5, θJA --------------------------------------------------------------------------------------------------------Junction Temperature Range -------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Mode) ---------------------------------------------------------------------------------------MM (Machine Mode) ------------------------------------------------------------------------------------------------ Recommended Operating Conditions z z z −0.3V to 6.5V −0.3V to (VIN + 0.3V) −0.3V to 6.5V 0.4W 250°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage ------------------------------------------------------------------------------------------------ 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 Quiescent Current IQ Reference Voltage VREF Under Voltage Lockout Threshold VUVLO Switching Frequency fSW Test Conditions VIN Rising Hysteresis Min Typ Max Unit -- 78 -- μA 0.588 0.6 0.612 V 2 -- 2.3 0.2 2.45 -- V 1.2 1.5 1.8 MHz PGOOD Low Threshold VFB Falling -- 85 -- %VREF PGOOD High Threshold VFB Rising -- 90 -- %VREF -- 150 -- °C Thermal Shutdown Temperature TSD Switch On Resistance, High RPFET ILX = 0.2A -- 250 -- mΩ Switch On Resistance, Low RNFET ILX = 0.2A -- 200 -- mΩ Peak Current Limit ILIM 1.1 1.5 2 A Output Voltage Line Regulation VIN = 2.7V to 5.5V -- 0.1 -- %/V Output Voltage Load Regulation 0A < ILOAD < 0.6A -- 1 -- %/A DS8060A-00 March 2011 www.richtek.com 3 RT8060A 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. Note 3. Devices are ESD sensitive. Handling precaution recommended. Note 4. The device is not guaranteed to function outside its operating conditions. www.richtek.com 4 DS8060A-00 March 2011 RT8060A Typical Operating Characteristics Reference Voltage vs. Input Voltage Efficiency vs. Load Current 0.620 100 0.615 90 Efficiency (%) 80 70 Reference Voltage (V) VIN = 3.8V VIN = 5V VIN = 5.5V 60 50 40 30 20 10 0 0.2 0.4 0.6 0.8 0.605 0.600 0.595 0.590 0.585 0.580 0.575 VOUT = 1.2V 0 0.610 IOUT = 0.6A 0.570 2.8 1 3.3 Reference Voltage vs. Temperature 4.8 5.3 Reference Voltage vs. Output Current 0.620 0.620 0.615 0.615 0.610 0.610 Reference Voltage (V) Reference Voltage (V) 4.3 Input Voltage (V) Load Current (A) 0.605 0.600 0.595 0.590 0.585 0.580 0.575 3.8 VIN = 5V, IOUT = 0.6A 0.605 0.600 VIN = 5.5V VIN = 5V VIN = 4.2V 0.595 0.590 0.585 0.580 0.575 VBuck = 12V 0.570 0.570 -50 -25 0 25 50 75 100 125 0.0 Temperature (°C) 0.2 0.4 0.6 0.8 1.0 Output Current (A) Load Transient Response Frequency vs. Temperature 1.60 Frequency (MHz)1 1.55 1.50 VOUT (50mV/Div) VIN = 3.6V 1.45 1.40 VIN = 5.5V 1.35 IOUT (500mA/Div) 1.30 1.25 IOUT = 0.5A VIN = 5.5V, IOUT = 50mA to 1A 1.20 -50 -25 0 25 50 75 100 125 Time (250μs/Div) Temperature (°C) DS8060A-00 March 2011 www.richtek.com 5 RT8060A Line Transient Response Switching VOUT (20mV/Div) VIN (2V/Div) I Inductor (500mA/Div) VOUT (10mV/Div) VLX (5V/Div) IOUT = 100mA VIN1 = 5.5V, IOUT = 500mA Time (100μs/Div) Time (250ns/Div) PGOOD Threshold vs. Temperature Switching 100% 100 Percent of V REF (%) VOUT (20mV/Div) I Inductor (1A/Div) VLX (5V/Div) VIN1 = 5.5V, IOUT = 1A Time (250ns/Div) 97 95% 94 Low to High 91 90% 88 85% 85 High to Low 82 80% 79 76 75% 73 70% 70 -50 VIN = 5.5V -25 0 25 50 75 100 125 Temperature (°C) www.richtek.com 6 DS8060A-00 March 2011 RT8060A Applications Information VOUT ⎤ ⎡ VOUT ⎤ ⎡ L=⎢ x 1 − ⎢ ⎥ ⎥ ⎣ f × ΔIL(MAX) ⎦ ⎢⎣ VIN(MAX) ⎥⎦ The basic RT8060A 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. A smaller inductor changes its current more quickly for a given voltage drive than a larger inductor, resulting in faster transient response. A larger inductor will reduce output ripple and current ripple, but at the expense of reduced transient performance and a physically larger inductor package size. For this reason, a larger capacitor, C1, will be required for larger inductor sizes. Inductor Selection For a given input and output voltage, the inductor value and operating frequency determine the ripple current. The ripple current ΔIL increases with higher VIN and decreases with higher inductance. The input regulator has an instantaneous peak current clamp to prevent the inductor from saturating during transient load or start-up conditions. The clamp is designed so that it does not interfere with normal operation at high loads and reasonable inductor ripple. It is intended to prevent inductor current runaway in case of a shorted output. ⎤ ⎡V ⎤ ⎡ V ΔIL = ⎢ OUT ⎥ x ⎢1− OUT ⎥ VIN ⎦ ⎣ f ×L ⎦ ⎣ Having a lower ripple current reduces the ESR losses in the output capacitors and the output voltage ripple. Highest efficiency operation is achieved at low frequency with small ripple current. This, however, requires a large inductor. The DC winding resistance and AC core losses of the inductor will also affect efficiency, and therefore available output power. These effects are difficult to characterize and vary by application. Some inductors and capacitors that may be suitable for this application are listed in Table below : A reasonable starting point for selecting the ripple current is ΔIL = 0.4(IMAX). The largest ripple current occurs at the highest VIN. To guarantee that the ripple current stays below a specified maximum, the inductor value should be chosen according to the following equation : Table Length Width Height Inductance RDC IDC (mm) (mm) (mm) (μH) (mΩ) (A) Max. Max. Max. L Max. Max. 5 5 3 4.8 4.8 2.8 1.2 1.4 1 1 2.2 2.2 50 73 120 3.3 3 1 VLF3012A VLS2010E VLS2012E 3 2.1 2.1 2.8 2.1 1.2 1 2.2 2.2 100 228 1 1 NR6045T1R0N CB2016T2R2M 6 2.2 2.1 6 1.8 1.2 4.5 1.8 2.2 1 2.2 153 19 130 1 4.2 1 NR6020T2R2N NR3015 6 3 6 3 2 1.5 2.2 2.2 34 60 2.7 1.48 LPS4018 3.9 3.9 1.7 3.3 80 2.2 CoilCraft D53LC DB318C 5 3.8 5 3.8 3 1.8 3.3 3.3 34 70 2.26 1.55 Toko WE-TPC Type M1 4.8 4.8 1.8 3.3 65 1.95 Wurth P/N VLF5012ST-1R0N2R5 VLF5014ST-2R2M2R3 VLF3010A-1 DS8060A-00 March 2011 Supplier TDK TAIYO www.richtek.com 7 RT8060A CIN and COUT Selection Using Ceramic Input and Output Capacitors The input capacitance, C IN, 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 : 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. IRMS = IOUT(MAX) VOUT x 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 as described in a later section. The output ripple, ΔVOUT, is determined by : 1 ⎤ ⎡ ΔVOUT ≤ ΔIL x ⎢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, specialpolymer, 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. www.richtek.com 8 Output Voltage Programming The resistive voltage divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 1. VOUT LX RT8060A R1 FB R2 GND Figure 1. Output Voltage Setting For adjustable voltage mode, the output voltage is set by an external resistive voltage divider according to the following equation : R1 VOUT = VREF × (1 + ) R2 where VREF is the internal reference voltage (0.6V typ.) Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to ΔILOAD (ESR), where ESR is the effective series resistance of COUT. ΔILOAD also begins to charge or discharge COUT, generating a feedback error signal used by the regulator to return VOUT to its steady-state value. During this recovery time, VOUT can be monitored for overshoot or ringing that would indicate a stability problem. DS8060A-00 March 2011 RT8060A PGOOD is an open-drain output that indicates whether the output voltage is ready or not. PGOOD is typically pulled up to 3.3V or tied with VIN. PGOOD is in high impedance when the voltage on FB pin exceeds the rising threshold 90% of VREF 0.6V (typ). PGOOD is in low impedance when the voltage on FB pin falls below the falling threshold 85% of VREF. If the voltage detector feature is not required, connect PGOOD to ground. VFB 85% VREF 90% VREF PGOOD The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. For the RT8060A package, the derating curve in Figure 3 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Maximum Power Dissipation (W)1 PGOOD Output 0.45 Single-Layer PCB 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 Figure 2. VFB and PGOOD Comparator Waveform Thermal Considerations 0 25 50 75 100 125 Ambient Temperature (°C) Figure 3. Derating Curves for RT8060A Package 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 : 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 RT8060A, the maximum junction temperature is 125°C and TA is the ambient temperature. The junction to ambient thermal resistance, θJA, is layout dependent. For SOT23-5 packages, the thermal resistance, θJA, is 250°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 : P D(MAX) = (125°C − 25°C) / (250°C/W) = 0.4W for SOT-23-5 package DS8060A-00 March 2011 www.richtek.com 9 RT8060A Outline Dimension H D L B C b A A1 e Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.889 1.295 0.035 0.051 A1 0.000 0.152 0.000 0.006 B 1.397 1.803 0.055 0.071 b 0.356 0.559 0.014 0.022 C 2.591 2.997 0.102 0.118 D 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 H 0.080 0.254 0.003 0.010 L 0.300 0.610 0.012 0.024 SOT-23-5 Surface Mount 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. www.richtek.com 10 DS8060A-00 March 2011