® RT8580 36V DC/DC Boost Converter General Description Features The RT8580 is a high performance, low noise, DC/DC Boost Converter with an integrated 0.5A, 1Ω internal switch. The RT8580's input voltage ranges from 3V to 5.5V, and it can support the output voltage up to 40V. When used in optical receiver applications requiring 80V to drive the APD (Avalanche Photo Diode), the output voltage of RT8580 can be doubled up by a typical voltage doubler circuit. The RT8580 adapts fixed frequency, current mode PWM control loop to regulate the output voltage with fast transient response and cycle-by-cycle current limit protection. The protection features of RT8580 include : 1) input undervoltage lockout, 2) output over-voltage protection, and 3) over-temperature protection. The soft-start function and PWM loop compensation is built-in internally to save external soft-start capacitor and PWM loop compensation components. By operating at 500kHz switching frequency, the RT8580 system board can be made compact to achieve low system BOM cost. The RT8580 is available in the tiny package type SOT-23-6. z Input Operating Range : 3V to 5.5V z Wide Output Range : VCC to 40V Internal Power N-MOSFET Switch 500kHz Fixed Switching Frequency Minimize the External Component Counts Internal Soft-Start Internal Compensation Under-Voltage Lockout Protection Over-Temperature Protection RoHS Compliant and Halogen Free z z z z z z z z Applications z z z z Cellular Phones Digital Cameras Portable Instruments Avalanche Photodiode Biasing Ordering Information RT8580 Package Type E : SOT-23-6 Marking Information Lead Plating System G : Green (Halogen Free and Pb Free) 0E= : Product Code 0E=DNN DNN : Date Code 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. Simplified Application Circuit D1 L1 VIN VOUT C1 RT8580 R1 VCC LX SHDN FB GND C2 R2 PGND Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8580-00 August 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8580 Pin Configurations (TOP VIEW) LX VCC SHDN 6 5 4 2 3 PGND GND FB SOT-23-6 Functional Pin Description Pin No. Pin Name Pin Function 1 PGND Power Ground. 2 GND Ground. 3 FB Feedback Voltage Input. Connect a resistor to GND to setting the current. 4 SHDN Shutdown Control Input. Apply a logic-low voltage to SHDN to shut down the device. Connect SHDN to VIN for normal operation. Ensure that SHDN is not greater than the input voltage, VCC. 5 VCC Supply Voltage Input. 6 LX Switch Node. Function Block Diagram LX GND VCC UVLO OCP Internal Compensation Internal Soft-Start OTP PWM Logic Control, Minimum On Time + + EA GM Driver PGND + - Slope Compensation LPF Enable Logic Shutdown 20ms 1µA FB PWM Oscillator Reference Voltage VREF Bias Current SHDN Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 CurrentSense is a registered trademark of Richtek Technology Corporation. DS8580-00 August 2013 RT8580 Operation The RT8580 is a constant frequency, current mode Boost regulator. In normal operation, the N-MOSFET is turned on when the PWM control circuit is set by the oscillator. As the N-MOSFET is on, the inductor current ramps up. The N-MOSFET will be turned off when the inductor current hits the level set by the PWM control loop. After the N-MOSFET is turned off, the inductor current will ramp down through the external catch diode until the OSC sets high for the next switching cycle and the next cycle repeats. The operation of the RT8580 can be better understood by referring to the block diagram. The voltage at the output of the error amplifier is an amplified version of the difference between the 1.25V reference voltage and the output feedback voltage. If the feedback voltage drops below (above) 1.25V, the output of the error amplifier increases (decreases). This results in higher (lower) PWM turn on duty and thus higher (lower) inductor peak current flowing through the power FET. By this control loop operation, the increased (decreased) power will be delivered to the output to bring up (down) the output feedback voltage back to 1.25V. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8580-00 August 2013 When the RT8580 is enabled by SHDN pin, the internal VREF ramps up to the target voltage in a specific time period. There is also a built-in soft-start function. Both ensure that the output voltage rises slowly to reduce the input inrush current. The protection features of RT8580 include : 1) input undervoltage lockout, 2) output over-voltage protection, and 3) over-temperature protection. When the input voltage is lower than the UVLO threshold, the RT8580 will be turned off. There is a 100mV hysteresis for the UVLO control. When the junction temperature exceeds 150°C, the overtemperature protection function will shut down the switching operation. Once the junction temperature cools down by approximately 25°C, the converter will automatically resume switching. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8580 Absolute Maximum Ratings z z z z z z z z (Note 1) VCC, SHDN, FB to GND -------------------------------------------------------------------------------------------------LX to GND -------------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C SOT-23-6 --------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SOT-23-6, θJA ---------------------------------------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ----------------------------------------------------------------------------------------------MM (Machine Model) ------------------------------------------------------------------------------------------------------ Recommended Operating Conditions z z z −0.3V to 6V −0.3V to 50V 0.48W 208.2°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Input Voltage, VCC --------------------------------------------------------------------------------------------------------- 3V to 5.5V Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VCC = 3.3V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit -- 2 2.4 V 0.6 0.8 1.2 mA -- 2 5 μA -- -- 2 μA Overall Under-Voltage Lockout Threshold VUVLO VCC Quiescent Current IQ VCC Shutdown Current Shutdown Input Current SHDN = 0V ISHDN Logic-High VIH 1.4 -- -- Logic-Low VIL -- -- 0.5 Switching Frequency fSW 450 500 550 kHz Maximum Duty in Steady State Operation DMAX 91 93 97 % -- 1 -- % 1.22 1.25 1.28 V -- 100 500 nA -- 0.7 1 Ω -- -- 4 μA -- 330 -- mA SHDN Threshold Voltage V Oscillator Line Regulation VCC = 3.3V to 4.3V Feedback Reference Voltage Feedback Input Current IFB LX On-Resistance RDS(ON) LX Leakage Current Switch Current Limit VFB = VFB_SET VLX = 40V ILIM Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8580-00 August 2013 RT8580 Parameter Symbol Test Conditions Min Typ Max Unit Thermal Protection Thermal Shutdown Temperature TSD -- 150 -- °C Thermal Shutdown Hysteresis ΔTSD -- 25 -- °C 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. DS8580-00 August 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8580 Typical Application Circuit VIN 3V to 5.5V D1 L1 C1 2.2µF RT8580 5 VCC 4 SHDN 2 GND 1 PGND Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 LX FB 6 VOUT 30V R1 150k C2 4.7µF 3 R2 6.2k is a registered trademark of Richtek Technology Corporation. DS8580-00 August 2013 RT8580 Typical Operating Characteristics Quiescent Current vs. Input Voltage Efficiency vs. Load Current 1000 90 950 Quiescent Current (µA) 100 Efficiency (%) 80 70 60 VIN = 5.5V VIN = 4.8V VIN = 3.3V 50 40 30 20 900 850 800 750 700 650 10 Device Not Switching VOUT = 30V 600 0 0 0.5 1 1.5 2 2.5 3 3.5 2 4 2.5 3 3.5 No Load Quiescent Current vs. Input Voltage 5 5.5 6 Quiescent Current vs. Temperature 16 900 14 Quiescent Current (µA) No Load Quiescent Current (mA)1 4.5 Input Voltage (V) Load Current (mA) 12 10 8 6 4 VIN = 5V 850 800 750 VIN = 3V 700 650 2 VOUT = 30V Device Not Switching 600 0 2.5 3 3.5 4 4.5 5 -50 5.5 -25 0 25 50 75 100 125 Temperature (°C) Input Voltage (V) Switching Frequency vs. Temperature Feedback Voltage vs. Temperature 520 1.30 515 510 Feedback Voltage (V) Switching Frequency (kHz)1 4 505 500 495 490 485 480 475 1.28 1.26 VIN = 5V VIN = 3V 1.24 1.22 VIN = 5V, VOUT = 30V 470 1.20 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8580-00 August 2013 125 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8580 Light Load Switching Heavy Load Switching VOUT_ac (2mV/Div) VOUT_ac (2mV/Div) LX (20V/Div) LX (20V/Div) IL (100mA/Div) IL (100mA/Div) VIN = 5V, VOUT = 30V, IOUT = 4mA VIN = 5V, VOUT = 30V, IOUT = 0.1mA Time (1μs/Div) Time (1μs/Div) Power On from SHDN Power Off from SHDN VOUT (20V/Div) VOUT (20V/Div) SHDN (5V/Div) SHDN (5V/Div) IL (100mA/Div) IL (100mA/Div) VIN = 5V, VOUT = 30V, IOUT = 2mA Time (10ms/Div) VIN = 5V, VOUT = 30V, IOUT = 2mA Time (50ms/Div) Load Transient Response VOUT_ac (100mV/Div) IOUT (2mA/Div) VIN = 5V, VOUT = 30V, IOUT = 0 to 4mA Time (1ms/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS8580-00 August 2013 RT8580 Application Information The RT8580 current-mode PWM controllers operate in wide range of DC/DC conversion applications for boost. This converter provides low noise, high output voltages. Other features include shutdown, fixed 500kHz PWM oscillator, and a input range : 3V to 5.5V for RT8580. The RT8580 operates in discontinuous mode in order to reduce the switching noise at the output. Other continuous mode Boost converters generate a large voltage spike at the output when the LX switch turns on because there is a conduction path between the output, diode, and switch to ground during the time needed for the diode to turn off. SHDN Input The SHDN pin provides shutdown control. Connect SHDN to VCC for normal operation. To disable the device, connect SHDN to GND. Constant Output Voltage Control The output voltage of the RT8580 is fixed at 30V. The output voltage is set by two external resistors (R1 and R2). First select the value of R2 in the 5kΩ to 50kΩ range. R1 is then given by : ⎛V ⎞ R1 = R2 ⎜ OUT − 1⎟ ⎝ VREF ⎠ where VREF is 1.25V Determining Peak Inductor Current If the Boost converter remains in the discontinuous mode of operation, then the approximate peak inductor current, ILPEAK, is represented by the formula below : ILPEAK = 2TS (VOUT − VIN )IOUT ηL where TS is the period, VOUT is the output voltage, VIN is the input voltage, IOUT is the output current, and η is the efficiency of the boost converter. Inductor Selection The recommended value of inductor for 30V, 22μH is the recommended inductor value when the output voltage is 30V and the input voltage is 5V. In general, the inductor Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8580-00 August 2013 should have a current rating greater than the current-limit value. The inductor saturation current rating should be considered to cover the inductor peak current. Soft-Start The function of soft-start is made for suppressing the inrush current to an acceptable value at the beginning of power on. The RT8580 provides a built-in soft-start function by clamping the output voltage of error amplifier so that the duty cycle of the PWM will be increased gradually in the soft-start period. Current Limiting The current flow through inductor as charging period is detected by a current sensing circuit. As the value comes across the current limiting threshold, the N-MOSFET will be turned off so that the inductor will be forced to leave charging stage and enter discharging stage. Therefore, the inductor current will not increase over the current limiting threshold. Diode Selection The RT8580's high switching frequency demands a highspeed rectifier. Schottky diodes are recommended for most applications because of their fast recovery time and low forward-voltage drop. Ensure that the diode's peak current rating is greater than or equal to the peak inductor current. Also, the diode reverse breakdown voltage must be greater than VOUT. Input Capacitor Selection Low ESR ceramic capacitors are recommended for input capacitor applications. Low ESR will effectively reduce the input voltage ripple caused by switching operation. A 4.7μF capacitor is sufficient for most applications. Nevertheless, this value can be decreased for lower output current requirement. Another consideration is the voltage rating of the input capacitor which must be greater than the maximum input voltage. is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8580 Over-Temperature Protection 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 SOT-23-6 package, the thermal resistance, θ JA, is 208.2°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) / (208.2°C/W) = 0.48W for SOT-23-6 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 1 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Maximum Power Dissipation (W)1 The RT8580 has Over-Temperature Protection (OTP) function to prevent the excessive power dissipation from overheating. The OTP function will shut down switching operation when the die junction temperature exceeds 150°C. The chip will automatically start to switch again when the die junction temperature cools off. 0.6 Four-Layer PCB 0.5 0.4 0.3 0.2 0.1 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 1. Derating Curve of Maximum Power Dissipation Layout Considerations PCB layout is very important when designing power switching converter circuits. Some recommended layout guide lines are as follows : The power components L1, D1 and C2 must be placed as close to each other as possible to reduce the ac current loop area. The PCB trace between power components must be as short and wide as possible due to large current flow through these traces during operation. Place L1 and D1 as close to the LX Pin as possible. The trace should be as short and wide as possible. The input capacitor C1 must be placed as close to the VCC pin as possible. Locate input capacitor as close to VCC as possible. Place these components as close as possible to the LX Pin. C1 VIN L1 D1 LX VCC SHDN 6 5 4 2 3 GND PGND GND FB R1 R2 C2 VOUT Figure 2. PCB Layout Guide Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS8580-00 August 2013 RT8580 Outline Dimension H D L C B b A A1 e Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 0.889 1.295 0.031 0.051 A1 0.000 0.152 0.000 0.006 B 1.397 1.803 0.055 0.071 b 0.250 0.560 0.010 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-23-6 Surface Mount 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. DS8580-00 August 2013 www.richtek.com 11