® RT6200 0.6A, 36V, 1.2MHz Step-Down Converter General Description Features The RT6200 is a high voltage Buck converter that can support the input voltage range from 4.5V to 36V and the output current can be up to 0.6A. Current mode operation provides fast transient response and eases loop stabilization. Wide Operating Input Voltage Range : 4.5V to 36V Adjustable Output Voltage Range : 0.8V to 15V 0.6A Output Current 0.35Ω Ω Internal Power MOSFET Switch High Efficiency up to 95% 1.2MHz Fixed Switching Frequency (Duty <90%) Support duty up to 95% Stable with Low ESR Output Ceramic Capacitors Thermal Shutdown Cycle-By-Cycle Over-Current Protection The chip also provides protection functions such as cycleby-cycle current limit and thermal shutdown protection. The RT6200 is available in the SOT-23-6 package. Ordering Information RT6200 Applications Package Type E : SOT-23-6 Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : RoHS compliant and compatible with the current require- Distributed Power Systems Battery Chargers Pre-Regulator for Linear Regulators WLED Drivers Pin Configurations (TOP VIEW) ments of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. PHASE VIN EN 6 5 4 2 3 Marking Information 0Q= : Product Code 0Q=DNN BOOT GND FB DNN : Date Code SOT-23-6 Simplified Application Circuit VIN BOOT VIN C1 RT6200 VOUT CB L1 PHASE D1 Enable EN R1 FB Open = Automatic Startup GND Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS6200-03 November 2014 C2 R2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT6200 Functional Pin Description Pin No. Pin Name Pin Function BOOT Bootstrap Supply for High-Side Gate Driver. A capacitor is connected between the PHASE and BOOT pins to form a floating supply across the power switch driver. This capacitor is needed to drive the power switch’s gate above the supply voltage. 2 GND Ground. This pin is the voltage reference for the regulated output voltage. For this reason, care must be taken in its layout. This node should be placed outside of the D1 to C1 ground path to prevent switching current spikes from inducing voltage noise into the part. 3 FB Feedback Voltage Input. An external resistor divider from the output to GND tapped to the FB pin sets the output voltage. The value of the divider resistors also set loop bandwidth. 4 EN Enable Control Input (Active High). If the EN pin is open, it will be pulled to high by internal circuit. 5 VIN Supply Voltage Input. Bypass VIN to GND with a suitable large capacitor to prevent large voltage spikes from appearing at the input. 6 PHASE Switch Node. 1 Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS6200-03 November 2014 RT6200 Function Block Diagram VIN - X20 1µA Current Sense Amp EN 3V 1.1V BOOT - Oscillator 1.2MHz + Shutdown Reference Comparator S Q + EA - FB 45mΩ Ramp Generator Regulator 10k + 400k 30pF + Driver R PWM Comparator PHASE Bootstrap Control OC Limit Clamp GND 2pF Operation The RT6200 is a constant frequency, current mode asynchronous step-down converter. In normal operation, the high side N-MOSFET is turned on when the S-R latch is set by the oscillator and is turned off when the current comparator resets the S-R latch. While the N-MOSFET is turned off, the inductor current conducts through the external diode. Error Amplifier The error amplifier adjusts its output voltage by comparing the feedback signal (VFB) with the internal 0.8V reference. When the load current increases, it causes a drop in the feedback voltage relative to the reference, the error amplifier's output voltage then rises to allow higher inductor current to match the load current. Internal Regulator The regulator provides low voltage power to supply the internal control circuits and the bootstrap power for highside gate driver. Enable The converter is turned on when the EN pin is higher than 1.2V and turned off when the EN pin is lower than 0.94V. When the EN pin is open, it will be pulled up to logic-high by 1μA current internally. Soft-Start (SS) An internal current source charges an internal capacitor to build a soft-start ramp voltage. The FB voltage will track the internal ramp voltage during soft-start interval. The typical soft-start time is 700μs. Oscillator The internal oscillator runs at fixed frequency 1.2MHz. The RT6200 can support duty up to 95% by decreasing switching frequency to 600kHz. In short circuit condition, the frequency is reduced for low power consumption. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS6200-03 November 2014 Thermal Shutdown The over temperature protection function will shut down the switching operation when the junction temperature exceeds 150°C. Once the junction temperature cools down by approximately 20°C, the converter will automatically resume switching. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT6200 Absolute Maximum Ratings (Note 1) Supply Voltage, VIN -------------------------------------------------------------------------------------------------PHASE Voltage ------------------------------------------------------------------------------------------------------BOOT Voltage --------------------------------------------------------------------------------------------------------Other Pins -------------------------------------------------------------------------------------------------------------Output Voltage -------------------------------------------------------------------------------------------------------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 40V −0.3V to (VIN + 0.3V) VPHASE + 6V 0.3V to 6V −0.3V to 15V 0.48W 208.2°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Supply Voltage, VIN -------------------------------------------------------------------------------------------------Output Voltage, VOUT -----------------------------------------------------------------------------------------------EN Voltage, VEN -----------------------------------------------------------------------------------------------------Junction Temperature Range --------------------------------------------------------------------------------------Ambient Temperature Range --------------------------------------------------------------------------------------- 4.5V to 36V 0.8V to 15V 0V to 5.5V −40°C to 125°C −40°C to 85°C Electrical Characteristics (VIN = 12V, TA = 25°C unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit 0.784 0.8 0.816 V -- 0.1 0.3 A Feedback Reference Voltage VFB 4.5V VIN 36V Feedback Current IFB VFB = 0.8V Switch On Resistance RDS(ON) VBOOT VPHASE = 4.8V -- 0.35 -- VEN = 0V, VPHASE = 0V -- -- 10 A Switch Leakage Current Limit ILIM VBOOT VPHASE = 4.8V, duty = 90% -- 1.2 -- A Oscillator Frequency f SW Duty < 90% 1 1.2 1.4 MHz -- 95 -- % -- 80 -- ns 3.9 4.2 4.5 V -- 200 -- mV Maximum Duty Cycle Minimum On-Time tON Under-Voltage Lockout Threshold Rising Under-Voltage Lockout Threshold Hysteresis EN Input Voltage Logic-High VIH 0.98 1.08 1.2 Logic-Low VIL 0.94 1 1.06 Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 V is a registered trademark of Richtek Technology Corporation. DS6200-03 November 2014 RT6200 Parameter Symbol EN Pull-Up Current Test Conditions Min Typ Max Unit VEN = 0V -- 1 -- A Shutdown Current ISHDN VEN = 0V -- 20 -- A Quiescent Current IQ VEN = 2V, VFB = 1V (Not Switching) -- 0.55 0.8 mA Thermal Shutdown TSD -- 150 -- °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 © 2014 Richtek Technology Corporation. All rights reserved. DS6200-03 November 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT6200 Typical Application Circuit VIN 5 C1 4.7µF Enable Open = Automatic Startup BOOT VIN RT6200 PHASE 6 CB 10nF L1 15µH D1 B250A 4 EN VOUT 5V R1 91k FB 3 GND 2 Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 1 C2 10µF R2 17.4k is a registered trademark of Richtek Technology Corporation. DS6200-03 November 2014 RT6200 Typical Operating Characteristics Efficiency vs. Output Current Output Voltage vs. Input Voltage 100 5.10 90 5.05 Output Voltage (V) Efficiency (%) 80 VIN = 7V VIN = 12V VIN = 17V 70 60 50 40 30 20 5.00 IOUT = 0.6A IOUT = 0.1A IOUT = 0A 4.95 4.90 4.85 10 VOUT = 5V VOUT = 5V 0 4.80 0 0.1 0.2 0.3 0.4 0.5 0.6 6 11 16 Output Current (A) Reference Voltage vs. Temperature 31 36 Output Voltage vs. Output Current 5.20 5.15 0.83 5.10 0.82 Output Voltage (V) Reference Voltage (V) 26 Input Voltage (V) 0.84 0.81 0.80 0.79 0.78 5.05 5.00 4.95 VIN = 7V VIN = 12V VIN = 17V 4.90 4.85 4.80 4.75 4.70 0.77 4.65 VIN = 12V, IOUT = 0.1A 0.76 VOUT = 5V 4.60 -50 -25 0 25 50 75 100 125 0 0.1 0.2 0.3 0.5 0.6 Frequency vs. Temperature Frequency vs. Input Voltage 1600 1500 1500 1400 1400 Frequency (kHz)a 1600 1300 1200 1100 1000 1300 1200 1100 1000 900 900 VOUT = 3.3V, IOUT = 0A VIN = 12V, VOUT = 3.3V 800 800 4 8 12 16 20 24 28 32 Input Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS6200-03 0.4 Output Current (A) Temperature (°C) Frequency (kHz) A 21 November 2014 36 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT6200 Load Transient Response Load Transient Response VOUT (50mV/Div) VOUT (50mV/Div) VIN = 12V, VOUT = 5V, IOUT = 50mA to 0.6A, L = 15μH IOUT (200mA/Div) VOUT (10mV/Div) VIN = 12V, VOUT = 5V, IOUT = 0.25A to 0.6A, L = 15μH IOUT (200mA/Div) Time (50μs/Div) Time (50μs/Div) Output Ripple Voltage Output Ripple Voltage VIN = 12V, VOUT = 5V, IOUT = 0.1A, L = 15μH VIN = 12V, VOUT = 5V, IOUT = 0.6A, L = 15μH VOUT (10mV/Div) VPHASE (10V/Div) VPHASE (10V/Div) I PHASE (200mA/Div) I PHASE (200mA/Div) Time (1μs/Div) Time (1μs/Div) Power On from EN Power Off from EN VIN = 12V, VOUT = 5V, IOUT = 0.6A VIN = 12V, VOUT = 5V, IOUT = 0.6A VOUT (5V/Div) VOUT (5V/Div) VEN (2V/Div) VEN (2V/Div) VPHASE (10V/Div) VPHASE (10V/Div) I PHASE (500mA/Div) I PHASE (500mA/Div) Time (200μs/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 Time (200μs/Div) is a registered trademark of Richtek Technology Corporation. DS6200-03 November 2014 RT6200 Application Information The RT6200 is a high voltage buck converter that can support the input voltage range from 4.5V to 36V and the output current can be up to 0.6A. Output Voltage Setting The resistive voltage divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 1. VOUT R1 FB RT6200 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 : VOUT = VFB 1 R1 R2 Where VFB is the feedback reference voltage (0.8V typ.). External Bootstrap Diode Connect a 10nF low ESR ceramic capacitor between the BOOT pin and PHASE pin. This capacitor provides the gate driver voltage for the high side MOSFET. It is recommended to add an external bootstrap diode between an external 5V and the BOOT pin for efficiency improvement when input voltage is lower than 5.5V or duty ratio is higher than 65%. The bootstrap diode can be a low cost one such as 1N4148 or BAT54. The external 5V can be a 5V fixed input from system or a 5V output of the RT6200. 5V BOOT RT6200 10nF PHASE Figure 2. External Bootstrap Diode Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS6200-03 November 2014 Inductor Selection The inductor value and operating frequency determine the ripple current according to a specific input and output voltage. The ripple current ΔIL increases with higher VIN and decreases with higher inductance. V V IL = OUT 1 OUT f L VIN Having a lower ripple current reduces not only the ESR losses in the output capacitors but also the output voltage ripple. High frequency with small ripple current can achieve highest efficiency operation. However, it requires a large inductor to achieve 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 the specified maximum, the inductor value should be chosen according to the following equation : VOUT VOUT L = 1 f IL(MAX) VIN(MAX) Inductor Core Selection The inductor type must be selected once the value for L is known. Generally speaking, high efficiency converters can not afford the core loss found in low cost powdered iron cores. So, the more expensive ferrite or mollypermalloy cores will be a better choice. The selected inductance rather than the core size for a fixed inductor value is the key for actual core loss. As the inductance increases, core losses decrease. Unfortunately, increase of the inductance requires more turns of wire and therefore the copper losses will increase. Ferrite designs are preferred at high switching frequency due to the characteristics of very low core losses. So, design goals can focus on the reduction of copper loss and the saturation prevention. Ferrite core material saturates “hard”, which means that inductance collapses abruptly when the peak design current is exceeded. The previous situation results in an abrupt increase in inductor ripple current and consequent output voltage ripple. Do not allow the core to saturate! is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT6200 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 do not radiate energy. However, they are usually more expensive than the similar powdered iron inductors. The rule for inductor choice mainly depends on the price vs. size requirement and any radiated field/ EMI requirements. Diode Selection When the power switch turns off, the path for the current is through the diode connected between the switch output and ground. This forward biased diode must have a minimum voltage drop and recovery times. Schottky diode is recommended and it should be able to handle those current. The reverse voltage rating of the diode should be greater than the maximum input voltage, and current rating should be greater than the maximum load current. CIN and COUT Selection The input capacitance, C IN, is needed to filter the trapezoidal current at the source of the top MOSFET. To prevent large ripple current, a low ESR input capacitor sized for the maximum RMS current should be used. The RMS current is given by : V IRMS = IOUT(MAX) OUT VIN 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 required Effective Series Resistance (ESR) to minimize voltage ripple. Moreover, the amount of bulk capacitance is also a key for COUT selection 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 VOUT IL ESR 8fC OUT Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 The output ripple will be highest at the 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 requirement. Dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are all available in surface mount packages. Special polymer capacitors offer very low ESR value. However, it provides lower capacitance density than other types. Although Tantalum capacitors have the highest capacitance density, it is important to only use types that pass the surge test for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR. However, it can be used in cost-sensitive applications for ripple current rating and long term reliability considerations. 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. 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 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. 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) also begins to charge or discharge COUT generating a feedback error signal for 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. is a registered trademark of Richtek Technology Corporation. DS6200-03 November 2014 RT6200 Thermal Considerations Layout Consideration For continuous operation, do not exceed the maximum operation junction temperature 125°C. 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. Follow the PCB layout guidelines for optimal performance of RT6200. The maximum power dissipation can be calculated by following formula : PD(MAX) = (TJ(MAX) − TA) / θJA 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). PHASE node is with high frequency voltage swing and should be kept at small area. Keep sensitive components away from the PHASE node to prevent stray capacitive noise pick-up. Place the feedback components to the FB pin as close as possible. Connect GND to a ground plane for noise reduction and thermal dissipation. 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 specifications, the maximum junction temperature of the die is 125°C. The junction to ambient thermal resistance θJA is layout dependent. For SOT-23-6 package, the thermal resistance θJA is 208.2°C/W on standard JEDEC 51-7 four-layers C OUT V OUT thermal test board. The maximum power dissipation at TA = 25°C can be calculated by following formula : L1 CB D1 PD(MAX) = (125°C − 25°C) / (208.2°C/W) = 0.48W for SOT-23-6 packages BOOT 1 6 PHASE GND 2 5 VIN FB 3 4 EN C IN The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance θJA. The derating curves in Figure 3 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. R2 V OUT R1 GND Figure 4. PCB Layout Guide Maximum Power Dissipation (W)1 1.0 Four-Layer PCB 0.8 0.6 0.4 0.2 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 3. Derating Curves of Maximum Power Dissipation Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS6200-03 November 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT6200 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 14F, No. 8, Tai Yuen 1st 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. www.richtek.com 12 DS6200-03 November 2014