® RT8062 2A, 2MHz, Synchronous Step-Down Converter General Description Features The RT8062 is a high efficiency synchronous, step-down DC/DC converter. Its input voltage range is from 2.7V to 5.5V and provides an adjustable regulated output voltage from 0.8V to 5V while delivering up to 2A of output current. z High Efficiency : Up to 95% z Adjustable Frequency : 200kHz to 2MHz No Schottky Diode Required 0.8V Reference Allows Low Output Voltage Low Dropout Operation : 100% Duty Cycle Enable Function Internal Soft-Start RoHS Compliant and Halogen Free The internal synchronous low on resistance power switches increase efficiency and eliminate the need for an external Schottky diode. The default switching frequency is set at 2MHz, if the RT pin is left open. It can also be varied from 200kHz to 2MHz by adding an external resistor. Current mode operation with external compensation allows the transient response to be optimized over a wide range of loads and output capacitors. z z z z z z Applications z z z Ordering Information RT8062 Package Type SP : SOP-8 (Exposed Pad-Option 2) z z LCD TV and Monitor Notebook Computers Distributed Power Systems IP Phones Digital Cameras Pin Configurations Lead Plating System G : Green (Halogen Free and Pb Free) COMP Note : Richtek products are : ` (TOP VIEW) RoHS compliant and compatible with the current require- 8 GND 2 EN 3 VIN 7 GND 6 9 4 5 FB RT LX LX ments of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. SOP-8 (Exposed Pad) Marking Information RT8062GSP : Product Number RT8062 GSPYMDNN YMDNN : Date Code Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8062-07 November 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8062 Typical Application Circuit RT8062 VIN 2.7V to 5.5V 4 VIN LX L 5, 6 VOUT R1 CIN 10µF FB 3 EN COMP 8 1 COUT RCOMP R2 CCOMP ROSC 7 RT GND 2, 9 (Exposed Pad) Note : Using all Ceramic Capacitors Table 1. Recommended Components Selection for fSW = 1MHz VOUT (V) R1 (kΩ) R2 (kΩ) R COMP (kΩ) CCOMP (pF) L (μH) COUT (μF) 3.3 75 24 33 560 2.0 22 2.5 51 24 22 560 2.0 22 1.8 30 24 15 560 1.5 22 1.5 21 24 13 560 1.5 22 1.2 12 24 11 560 1.5 22 1.0 6 24 8.2 560 1.5 22 Functional Pin Description Pin No. Pin Name Pin Function Error Amplifier Compensation Point. The current comparator threshold increases 1 COMP with this control voltage. Connect external compensation elements to this pin to stabilize the control loop. 2, GND 9 (Exposed Pad) 3 EN 4 VIN 5, 6 LX 7 RT Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Enable Control Input. Float or connect this pin to logic high for enable. Connect to GND for disable. Power Input Supply. Decouple this pin to GND with a capacitor. Internal Power MOSFET Switches Output. Connect these pins to the inductor together. Oscillator Resistor Input. Connecting a resistor from this pin to GND sets the switching frequency. If this pin is floating, the frequency will be set at 2MHz internally. 8 FB Feedback. Receives the feedback voltage from a resistive divider connected across the output. Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8062-07 November 2012 RT8062 Function Block Diagram RT SD VIN ISEN OSC Slope Com COMP 0.8V EA FB Output Clamp OC Limit Driver Int-SS LX Hiccup Control Logic 0.7V EN Enable 0.4V P-G UV Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8062-07 November 2012 NISEN OTP GND N-MOS ILIM is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8062 Absolute Maximum Ratings z z z z z z z z z z (Note 1) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------LX Pin Switch Voltage ---------------------------------------------------------------------------------------------<10ns -----------------------------------------------------------------------------------------------------------------Other I/O Pin Voltages --------------------------------------------------------------------------------------------LX Pin Switch Current ---------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SOP-8 (Exposed Pad), θJA ---------------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJC --------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------- Recommended Operating Conditions z z z −0.3V to 6.5V −0.3V to (VIN + 0.3V) −5V to 8.5V −0.3V to (VIN + 0.3V) 5A 1.33W 75°C/W 15°C/W 150°C 260°C −65°C to 150°C 2kV (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 = 3.3V, TA = 25°C, unless otherwise specified) Parameter Min Typ Max Unit 0.784 0.800 0.816 V Active , VFB = 0.78V, Not Switching -- 460 -- Shutdown -- -- 10 Output Voltage Line Regulation VIN = 2.7V to 5.5V -- 0.1 -- %/V Output Voltage Load Regulation 0A < ILOAD < 2A -- 0.25 -- % gm -- 400 -- μA/V Current Sense Trans-resistance RT -- 0.3 -- Ω ROSC = 300k 0.8 1 1.2 Switching 0.2 -- 2 Feedback Reference Voltage Symbol VREF DC Bias Current Error Amplifier Trans-conductance Switching Frequency EN Input Voltage Test Conditions fSW Logic-High VIH 1.6 -- -- Logic-Low VIL -- -- 0.4 Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 μA MHz V is a registered trademark of Richtek Technology Corporation. DS8062-07 November 2012 RT8062 Parameter Symbol Test Conditions Min Typ Max Unit Switch On Resistance, High RDS(ON)_P ILX = 0.5A -- 180 250 mΩ Switch On Resistance, Low RDS(ON)_N ILX = 0.5A -- 120 160 mΩ Peak Current Limit ILIM 2.4 3.5 -- A VIN Rising -- 2.4 -- VIN Falling -- 2.2 -- Under Voltage Lockout Threshold RT Shutdown Threshold VRT -- VIN − 0.7 VIN − 0.4 V V 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. θJC is measured at 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. Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8062-07 November 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8062 Typical Operating Characteristics Output Voltage vs. Output Current Efficiency vs. Output Current 100 1.130 90 1.125 1.120 1.115 Output Voltage (V) Efficiency (%) 80 70 60 50 40 30 1.110 1.105 1.100 1.095 1.090 1.085 20 1.080 10 1.075 VIN = 5V, VOUT = 1.1V, IOUT = 0A to 2A VIN = 5V, VOUT = 1.1V, IOUT = 0A to 2A 1.070 0 0 0.4 0.8 1.2 1.6 0 2 0.4 0.8 Switching Frequency vs. Temperature 2 Reference Voltage vs. Temperature 1.10 0.84 1.09 0.83 1.08 Reference Voltage (V) Switching Frequency (MHz)1 1.6 Output Current (A) Output Current (A) 1.07 1.06 1.05 1.04 1.03 1.02 0.82 0.81 0.80 0.79 0.78 0.77 1.01 VIN = 5V, VOUT = 1.1V, IOUT = 0.6A 1.00 -50 -25 0 25 50 75 100 VIN = 5V, VOUT = 1.1V 0.76 -50 125 -25 0 25 50 75 100 125 Temperature (°C) Temperature (°C) VIN UVLO vs. Temperature Enable Voltage vs. Temperature 2.8 1.6 2.7 1.5 2.6 1.4 Enable Voltage (V) VIN UVLO (V) 1.2 2.5 Turn On 2.4 2.3 2.2 Turn Off 2.1 1.3 1.1 1.0 Turn Off 0.9 2.0 0.8 1.9 0.7 1.8 Turn On 1.2 0.6 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 125 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS8062-07 November 2012 RT8062 Load Transient Response VOUT (100mV/Div) IOUT (1A/Div) Output Voltage Ripple VLX (5V/Div) VOUT (10mV/Div) VIN = 5V, VOUT = 1.1V, IOUT = 1A to 2A, RCOMP = 10kΩ, CCOMP = 560pF VIN = 5V, IOUT = 2A Time (100μs/Div) Time (500ns/Div) Power On from EN Power Off from EN VEN (5V/Div) VEN (5V/Div) VLX (5V/Div) VLX (5V/Div) VOUT (1V/Div) IOUT (2A/Div) VOUT (1V/Div) IOUT (2A/Div) VIN = 5V, VOUT = 1.1V, IOUT = 2A Time (250μs/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8062-07 November 2012 VIN = 5V, VOUT = 1.1V, IOUT = 2A Time (250μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8062 Application Information Main Control Loop During normal operation, the internal top power switch (P-MOSFET) is turned on at the beginning of each clock cycle. Current in the inductor increases until the peak inductor current reach the value defined by the output voltage (VCOMP) of the error amplifier. The error amplifier adjusts its output voltage by comparing the feedback signal from a resistor divider on the FB pin with an internal 0.8V reference. When the load current increases, it causes a reduction in the feedback voltage relative to the reference. The error amplifier raises its output voltage until the average inductor current matches the new load current. When the top power MOSFET shuts off, the synchronous power switch (N-MOSFET) turns on until the beginning of the next clock cycle. Output Voltage Setting The output voltage is set by an external resistive divider according to the following equation : VOUT = VREF × (1+ R1 ) R2 Operating Frequency Selection of the operating frequency is a tradeoff between efficiency and component size. High frequency operation allows the use of smaller inductor and capacitor values. Operation at lower frequency improves efficiency by reducing internal gate charge and switching losses but requires larger inductance and/or capacitance to maintain low output ripple voltage. The operating frequency of the IC is determined by an external resistor , ROSC, that is connected between the RT pin and ground. The value of the resistor sets the ramp current that is used to charge and discharge an internal timing capacitor within the oscillator. The practical switching frequency can range from 200kHz to 2MHz. However, when the RT pin is floating, the internal frequency is set at 2MHz. Determine the RT resistor value by examining the curve below. Please notice the minimum on time is about 90ns. 2.4 Switching Frequency (MHz)1 The basic IC 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. 2.0 1.6 1.2 0.8 0.4 where VREF equals to 0.8V typical. 0.0 The resistive divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 1. VOUT 0 300 600 900 1200 1500 1800 2100 RRT (kΩ) Figure 2. Switching Frequency vs. RRT Resistor R1 Inductor Selection FB RT8062 R2 GND Figure 1. Setting the Output Voltage Soft-Start The IC contains an internal soft-start clamp that gradually raises the clamp on the COMP pin. Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 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 ⎥ VIN ⎦ ⎣ f ×L ⎦ ⎣ is a registered trademark of Richtek Technology Corporation. DS8062-07 November 2012 RT8062 Having a lower ripple current reduces not only the ESR losses in the output capacitors but also the output voltage ripple. Highest efficiency operation is achieved by reducing ripple current at low frequency, but it requires a large inductor to attain this goal. For the ripple current selection, the value of ΔIL = 0.4(IMAX) will be a reasonable starting point. 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 : ⎡ VOUT ⎤ ⎡ ⎤ V L= ⎢ ⎥ ⎢1− OUT ⎥ ⎣⎢ f × ΔIL(MAX) ⎦⎥ ⎣⎢ VIN(MAX) ⎦⎥ Using Ceramic Input and Output Capacitors Higher values, 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. Slope Compensation and Inductor Peak Current Slope compensation provides stability in constant frequency architectures by preventing sub harmonic oscillations at duty cycles greater than 50%. It is accomplished internally by adding a compensating ramp to the inductor current signal. Normally, the maximum inductor peak current is reduced when slope compensation is added. In IC, however, separated inductor current signal is used to monitor over current condition and this keeps the maximum output current relatively constant regardless of duty cycle. Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8062-07 November 2012 Hiccup Mode Under Voltage Protection A Hiccup Mode Under Voltage Protection (UVP) function is provided for the IC. When the FB voltage drops below half of the feedback reference voltage, VFB, the UVP function will be triggered to auto re-softstart the power stage until this event is cleared. The Hiccup Mode UVP can reduce input current in short circuit conditions, and not be triggered during softstart process. Under Voltage Lockout Threshold The IC exists an input under voltage lockout protection (UVLO). If the input voltage exceeds the UVLO rising threshold voltage, the converter will reset and prepare the PWM for operation. If the input voltage falls below the UVLO falling threshold voltage during normal operation, the device will stop switching. The UVLO rising and falling threshold voltage exist a hysteresis to prevent noise caused reset. Thermal 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 : 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, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For SOP-8 (Exposed Pad) packages, the thermal resistance, θJA, is 75°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 : P D(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W for SOP-8 (Exposed Pad) package is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8062 The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. 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 1.4 Layout Considerations Follow the PCB layout guidelines for optimal performance of the IC. ` 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. ` 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. ` Connect the FB pin directly to the feedback resistors. The resistive voltage divider must be connected between VOUT and GND. Four-Layer PCB 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 3. Derating Curve of Maximum Power Dissipation Place the compensation components as close to the IC as possible Place the feedback resistors as close to the IC as possible GND R2 CCOMP COMP RCOMP FB 7 GND 6 9 4 5 GND 2 RT EN 3 LX VIN VIN R1 8 CIN VOUT ROSC GND LX L1 COUT VOUT Place the input and output capacitors as close to the IC as possible LX should be connected to inductor by wide and short trace, and keep sensitive components away from this trace Figure 4. PCB Layout Guide Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS8062-07 November 2012 RT8062 Outline Dimension H A M EXPOSED THERMAL PAD (Bottom of Package) Y J X B F C I D Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 4.801 5.004 0.189 0.197 B 3.810 4.000 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.510 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.170 0.254 0.007 0.010 I 0.000 0.152 0.000 0.006 J 5.791 6.200 0.228 0.244 M 0.406 1.270 0.016 0.050 X 2.000 2.300 0.079 0.091 Y 2.000 2.300 0.079 0.091 X 2.100 2.500 0.083 0.098 Y 3.000 3.500 0.118 0.138 Option 1 Option 2 8-Lead SOP (Exposed Pad) Plastic Package Richtek Technology Corporation 5F, No. 20, Taiyuen 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. DS8062-07 November 2012 www.richtek.com 11