RT8032 1.2MHz/1.2A Buck Converter with Programmable Average Input Current Limit General Description The RT8032 is a synchronous, step-down DC/DC converter with input current limit function. The average input current limit can be programmed by an external resistor. Its input voltage range is from 3V to 5.5V and provides an adjustable regulated output voltage from 0.8V to 5V while delivering up to 1.2A of output current. The internal synchronous low on-resistance power switches increase efficiency and eliminate the need for an external Schottky diode. Current mode operation with external compensation allows the transient response to be optimized over a wide range of loads and output capacitors. The RT8032 is operated in forced continuous PWM Mode which minimizes ripple voltage and reduces the noise and RF interference. The 100% duty cycle in Low Dropout Operation can maximize the battery life. Ordering Information RT8032 Features z z z z z z z z z z z z z Lead Plating System G : Green (Halogen Free and Pb Free) Small 12-Lead WDFN Package External Compensation for Optimal Transient Response External Soft-Start Input Over Voltage Protection RoHS Compliant and Halogen Free Applications z z Package Type QW : WDFN-12L 4x3 (W-Type) Programmable Average Input Current Limit 3V to 5.5V Input Range 1.2A Output Current Up to 95% Efficiency 1.2MHz Switching Frequency No Schottky Diode Required Force Continues Mode Operation Low RDS(ON) Internal Switches : 230mΩ Ω z z z Distributed Power Systems Battery Charger DSL Modems Pre-Regulator for Linear Regulators 3G/3.5G Data Card 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. Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area. DS8032-02 March 2011 (TOP VIEW) SHDN/SS NC GND SW PGND VOUT 1 2 3 4 5 6 PGND ` Pin Configurations 13 12 11 10 9 8 7 FB COMP ISET VIN VOUT NC WDFN-12L 4x3 www.richtek.com 1 RT8032 Typical Application Circuit RT8032 9 VIN V IN R SS 1Meg C IN 10µF 1 SHDN/SS C SS 57nF SW 4 VOUT 6, 8 FB 12 COMP 11 L 4.7µH R1 112k RC CC 120k 60nF R2 32k V OUT 3.6V C OUT 2200nF 10 ISET C C1 680nF R C1 1k R LIM 24k GND 3 PGND C C2 1.1nF 5, Exposed Pad (13) Functional Pin Description Pin No. 1 2, 7 Pin Name Pin Function Shutdown and Soft-Start Control Input. Connect this pin to a supply voltage that is >1.4V to enable the IC and to a supply voltage that is <0.4V to shutdown the IC. An SHDN/SS RC network from the shutdown command signal to the pin will provide a soft-start function by the rising time of the FB pin NC No Internal Connection. 3 GND Ground. Return the feedback resistive dividers to this ground, which in turn connects to PGND at one point. 4 SW Internal Power MOSFET Switches Output. Connect this pin to the output inductor. 5, PGND 13 (Exposed Pad) 6, 8 Power Ground. The exposed pad must be soldered to a large PCB and connected to PGND for maximum power dissipation. VOUT Output of the Converter. A filter capacitor is placed from VOUT to GND. 9 VIN Power Input. Internal VCC for the IC. A 10μF ceramic capacitor is recommended as close as to VIN and GND as possible 10 ISET Average Input Current Limit Setting. Place a resistor and capacitor in parallel from the pin to GND 11 COMP Error Amplifier Output. The current comparator threshold increases with the control voltage. Connect external compensation elements to the Pin to stabilize the control loop. 12 FB Feedback Input. Receives the feedback voltage from a resistive divider connected across the output. www.richtek.com 2 DS8032-02 March 2011 RT8032 Function Block Diagram Current Sense VOUT VIN Slope Com Soft-Start OSC OC Limit + + - Error Amplifier - V REF + SHDN/SS Driver COMP 0.4V FB + SW PWM Control - VIN PGND 0.95V GND + - Input Current Limit Setting OTP ISET DS8032-02 March 2011 www.richtek.com 3 RT8032 Absolute Maximum Ratings z z z z z z z z z (Note 1) Supply Input Voltage, VIN ---------------------------------------------------------------------------------------- −0.3V to 6V Switching Voltage, SW ------------------------------------------------------------------------------------------ −0.3V to (VIN+ 0.3V) Other I/O Pin Voltages ------------------------------------------------------------------------------------------- −0.3V to 6V Power Dissipation, PD @ TA = 25°C WDFN-12L 4x3 ----------------------------------------------------------------------------------------------------- 1.667W Package Thermal Resistance (Note 2) WDFN-12L 4x3, θJA ----------------------------------------------------------------------------------------------- 60°C/W WDFN-12L 4x3, θJC ----------------------------------------------------------------------------------------------- 7.5W Junction Temperature --------------------------------------------------------------------------------------------- 150°C Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------- 260°C Storage Temperature Range ------------------------------------------------------------------------------------ −65°C to 150°C ESD Susceptibility (Note 3) HBM (Human Body Mode) -------------------------------------------------------------------------------------- 2kV MM (Machine Mode) ---------------------------------------------------------------------------------------------- 200V Recommended Operating Conditions z z (Note 4) Junction Temperature Range ------------------------------------------------------------------------------------ −40°C to 125°C Ambient Temperature Range ------------------------------------------------------------------------------------ −40°C to 85°C Electrical Characteristics (VIN = 5V, TA = 25°C, unless otherwise specified) Parameter Feedback Reference Voltage Symbol Test Conditions VREF Min Typ Max Unit 0.784 0.8 0.816 V DC Bias Current (PVDD, VDD total) Active, Not Switching, VFB = 0.75V -- 550 -- μA EN =0 -- -- 1 μA Under Voltage Lockout Threshold VIN Rising 2.3 2.43 2.55 V VIN Falling 2.13 2.29 2.43 V 1 1.2 1.4 MHz Switching Frequency Logic-High Voltage VIH EN Threshold Logic-Low Voltage VIL VEN Rising 1.4 -- -- V VEN Falling -- -- 0.4 V Switch On Resistance, High RPMOS ISW = 0.2A -- 230 -- mΩ Switch On Resistance, Low RNMOS ISW = 0.2A -- 230 -- mΩ Input Average Current Limit I AVG RLIM = 25.5kΩ 0.4 0.45 0.5 A Peak Current Limit I LIM 1.6 1.9 -- A VIN = 3V to 5.5V -- 0.1 1 %/V 0mA < I LOAD < 1.2A -- -- 1 % Output Voltage Line Regulation Output Voltage Load Regulation www.richtek.com 4 DS8032-02 March 2011 RT8032 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 the natural convection at TA = 25°C on 4-layers high effective thermal conductivity test board of JEDEC 51-7 thermal measurement standard. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. DS8032-02 March 2011 www.richtek.com 5 RT8032 Typical Operating Characteristics Output Voltage vs. Output Current 3.65 90 3.64 80 3.63 Output Voltage (V) Efficiency (%) Efficiency vs. Output Current 100 70 60 50 40 30 20 3.62 3.61 3.60 3.59 3.58 3.57 10 3.56 VIN = 5V, VOUT = 3.6V VIN = 5V 3.55 0 0 0.2 0.4 0.6 0.8 1 1.2 0 0.2 0.4 1 1.2 Output Voltage vs. Temperature Reference Voltage vs. Input Voltage 0.814 3.65 3.64 0.812 3.63 Output Voltage (V) Reference Voltage (V) 0.8 Output Current (A) Output Current (A) 0.810 0.808 0.806 0.804 3.62 3.61 3.60 3.59 3.58 3.57 0.802 3.56 VOUT = 3.6V, IOUT = 0A VIN = 5V, IOUT = 0A 0.800 3.55 4 4.25 4.5 4.75 5 5.25 5.5 -50 -25 0 25 50 75 100 125 Temperature (°C) Input Voltage (V) Frequency vs. Input Voltage Frequency vs. Temperature 1.40 1.40 1.35 1.35 1.30 1.30 Frequency (MHz) Frequency (MHz) 0.6 1.25 1.20 1.15 1.10 1.25 1.20 1.15 1.10 1.05 1.05 VOUT = 3.6V, IOUT = 0A VIN = 5V, VOUT = 3.6V, IOUT = 0A 1.00 1.00 4 4.25 4.5 4.75 5 Input Voltage (V) www.richtek.com 6 5.25 5.5 -50 -25 0 25 50 75 100 125 Temperature (°C) DS8032-02 March 2011 RT8032 Input Current limit vs Temperature 0.60 0.55 0.55 Input Current limit (A) Input Current limit (A) Input Current Limit vs input Voltage 0.60 0.50 0.45 0.40 0.50 0.45 0.40 0.35 0.35 IOUT = 1A, RLIM = 24kΩ 0.30 VIN = 5V, IOUT = 1A, RLIM = 24kΩ 0.30 4 4.25 4.5 4.75 5 5.25 5.5 -50 -25 0 25 50 75 100 125 Temperature (°C) Input Voltage (V) Input Current Limit Switching VOUT (5mV/Div) VOUT (2V/Div) VSW (5V/Div) IOUT (1A/Div) I IN (500mA/Div) IL (500mA/Div) VIN = 5V, VOUT = 3.6V, IOUT = 0A to 1.5A VIN = 5V, VOUT = 3.6V, IOUT = 0.5A Time (2.5ms/Div) Time (500ns/Div) Power On from VIN Power Off from VIN VIN (5V/Div) VOUT (5V/Div) VIN (5V/Div) I IN (500mA/Div) VOUT (5V/Div) I IN (500mA/Div) IOUT (500mA/Div) IOUT (500mA/Div) IOUT = 0.33A Time (10ms/Div) DS8032-02 March 2011 IOUT = 0.33A Time (10ms/Div) www.richtek.com 7 RT8032 Application Information Output Voltage Programming The output voltage is set by an external resistive divider according to the following equation : VOUT = VREF × ⎛⎜1 + R1 ⎞⎟ ⎝ R2 ⎠ where VREF equals to 0.8V typical. The resistive divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 1. V OUT R1 FB RT8032 R2 GND Figure 1. Setting the Output Voltage Input Average Current Limit Setting The input current limit circuit is programmed by an external resistor on ISET. This allows the user to program a maximum average input current. For applications such as USB that the current from the bus must be limited, the value of RLIM and CC1 can be calculated as following equation. RLIM = 0.8 / (70 x 10-6 x IIN (A)) CC1 = 16 x 10-6 / RLIM,, RC1 = 1kΩ Soft-Start The soft-start function is combined with shutdown. When the SHDN/SS pin is brought above 1V (typ.), the IC will be enabled. The components of RSS and CSS provide a slow ramping voltage on the SHDN/SS pin to provide a soft-start function. Input Over Voltage Protection The RT8032 equips input over voltage protection function. When the input voltage exceeds 6V, the next switching cycle of the IC will be terminated. Once the input voltage is lower than 6V, the IC will enter normal operation again. 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 www.richtek.com 8 the main switch to remain on for more than one cycle and 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. 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. ⎡V ⎤⎡ V ⎤ ΔIL = ⎢ OUT ⎥ ⎢1 − OUT ⎥ f L × V IN ⎦ ⎣ ⎦⎣ Inductor Core Selection Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite or mollypermalloy cores. Actual core loss is independent of core size for a fixed inductor value but it is very dependent on the inductance selected. As the inductance increases, core losses decrease. Unfortunately, increased inductance requires more turns of wire and therefore copper losses will increase. Ferrite designs have very low core losses and are preferred at high switching frequencies, so design goals can concentrate on copper loss and preventing saturation. Ferrite core material saturates “hard”, which means that inductance collapses abruptly when the peak design current is exceeded. This result in an abrupt increase in inductor ripple current and consequent output voltage ripple. Do not allow the core to saturate! Different core materials and shapes will change the size/ current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy materials are small and don't radiate energy but generally cost more than powdered iron core inductors with similar characteristics. The choice of which style inductor to use mainly depends on the price vs. size requirements and any radiated field/EMI requirements. DS8032-02 March 2011 RT8032 CIN and COUT Selection Thermal Considerations 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 : For continuous operation, do not exceed absolute maximum operation junction temperature. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junction to ambient. The maximum power dissipation can be calculated by following formula : VIN −1 VOUT This formula has a maximum at VIN = 2VOUT, where I RMS = I OUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. 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 ⎢ESR + ⎥ 8fC OUT ⎦ ⎣ 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. DS8032-02 March 2011 PD(MAX) = (TJ(MAX) − TA) / θJA Where T J(MAX) is the maximum operation junction temperature, TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. For recommended operating conditions specification of RT8032, The maximum junction temperature is 125°C. The junction to ambient thermal resistance θJA is layout dependent. For WDFN-12L 4x3 packages, the thermal resistance θJA is 60°C/W on the standard JEDEC 51-7 four layers thermal test board. The maximum power dissipation at TA = 25°C can be calculated by following formula : PD(MAX) = (125°C − 25°C) / (60°C/W) = 1.667W for WDFN-12L 4x3 The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance θJA. For RT8032 package, the Figure 2 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power dissipation allowed. 1.8 Maximum Power Dissipation (W) V IRMS = IOUT(MAX) OUT VIN Four Layers PCB 1.6 1.4 WDFN-12L 4x3 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 2. Derating Curves for RT8032 Package www.richtek.com 9 RT8032 Layout Consideration Follow the PCB layout guidelines for optimal performance of RT8032. ` Keep the traces of the main current paths as short and wide as possible. ` Put the input capacitor as close as possible to the device pins (VIN and GND). ` LX node is with high frequency voltage swing and should be kept at small area. Keep analog components away from the LX node to prevent stray capacitive noise pickup. ` Connect feedback network behind the output capacitors. Keep the loop area small. Place the feedback components near the RT8032. ` Connect all analog grounds to a command node and then connect the command node to the power ground behind the output capacitors. ` An example of PCB layout guide is shown in Figure 3 for reference. R2 R1 C SS SHDN/SS NC GND SW L PGND VOUT 12 1 2 3 4 PGND R SS V IN 5 6 11 10 9 8 13 7 V OUT CC FB C C2 RC COMP C C1 ISET R C1 VIN R LIM VOUT C IN NC C OUT Figure 3. PCB Layout Guide Recommended component selection for Typical Application Component Supplier TAIYO YUDEN Series NR3015 Table 1. Inductors Inductance (μH) DCR (mΩ) Current Rating (mA) Dimensions (mm) 4.7 120 1020 3x3x1.5 Table 2. Capacitors for CIN and COUT Component Supplier TDK TAIYO YUDEN VISHAY www.richtek.com 10 Part No. C2012X5R0J106M JMK212BJ106ML 592D228X06R3X2T269 Capacitance (μF) 10 10 2200 Case Size 0805 0805 1415x7.37x2.2 (mm) DS8032-02 March 2011 RT8032 Outline Dimension 2 1 2 1 DETAIL A Pin #1 ID and Tie Bar Mark Options 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 0.180 0.300 0.007 0.012 D 3.950 4.050 0.156 0.159 D2 3.250 3.350 0.128 0.132 E 2.950 3.050 0.116 0.120 E2 1.650 1.750 0.065 0.069 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 12L DFN 4x3 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. DS8032-02 March 2011 www.richtek.com 11