RT6208 High Efficiency, 36V 100mA Synchronous Step-Down Converter General Description Features The RT6208 is a high-efficiency, monolithic synchronous step-down DC/DC converter that can deliver up to Achieves Very High Efficiency in Low Load Conditions 100mA output current from a 4.75V to 36V input supply. 1% High Accuracy Feedback Voltage It requires only 25A typical supply current at no load 4.75V to 36V Input Voltage Range while maintaining output voltage regulation. The RT6208 100mA Output Current achieves Boundary Conduction Mode (BCM) operation, Integrated High-Side and Low-Side Switches low quiescent current and programmable high-side peak No Compensation Required current limit, providing high efficiency over a wide range Low Quiescent Current of load currents. It also provides soft-start protection to Adjustable Peak Current Limit eliminate input current surge during start-up. The low Cycle-by-Cycle Over Current Protection current output Input Under Voltage Lockout disconnect, enabling easy power management in Internal Soft-Start battery-powered systems. The RT6208 is available in a Thermal Shutdown Protection (3A) shutdown mode provides SOT-23-6 and SOT-23-8 packages. Ordering Information RT6208 Package Type E : SOT-23-6 V8 : SOT-23-8 Lead Plating System G : Green (Halogen Free and Pb Free) 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 Applications Wireless Charger Industrial and Commercial Low Power Systems Green Electronics/Appliances Point of Load Regulation for High-Performance DSPs MCU Supply in Wireless LED Lighting Marking Information RT6208GE 30=DNN 30= : Product Code DNN : Date Code RT6208GV8 0E=DNN Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6208-02 May 2016 0E= : Product Code DNN : Date Code is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT6208 Pin Configurations AGND 3 8 7 6 5 2 3 4 SW 2 PGOOD 4 VIN 5 FB 6 GND SW VIN ISET EN (TOP VIEW) ISET FB GND EN SOT-23-6 SOT-23-8 Functional Pin Description Pin No Pin Name Pin Function SOT-23-6 SOT-23-8 1 7 FB Feedback Voltage Input. This pin receives the feedback voltage from a resistive divider connected across the output. 2 2 GND Power Ground. EN Enable Control Input. A voltage on this pin above 1.25V enables the converter into normal mode; forcing this pin below 0.3V shuts down the IC, reducing quiescent current to 3A. An internal 2A current pulls up enable pin for automatic startup. 3 8 4 1 ISET High-Side Peak Current Set Pin. A resistor from this pin to GND sets the high-side peak current limit. Leave floating for the maximum peak current, 225mA. Short this pin to GND for the minimum peak current, 50mA. A 1A current is sourced out of this pin. 5 3 VIN Input Supply Voltage. Must bypass with a suitably large ceramic capacitor. 6 4 SW Switch Node. Connect The Switching Node To External Inductor. -- 6 PGOOD Power Good Open Drain Output. Asserts low if output voltage is low due to OTP, UVP, UVLO, EN shutdown or during soft-start. -- 5 AGND Analog Ground. Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS6208-02 May 2016 RT6208 Function Block Diagram VIN VCC ISET 2V UVLO 1μA HS Switch Current Comparator 2μA - EN 5k 6V FB 1.21 + Shutdown Comparator 1ms Ramp SW FB Comparator LS Switch Current Comparator AGND PGOOD Current Sense Logic & Deadtime Control + + 0.8V Internal Regulator PGOOD Generator Current Sense GND Operation The RT6208 is a step-down DC/DC converter with comparators are disabled, reducing the VIN pin supply internal power switches that uses Hysteresis Mode current to only 25A. As the load current discharges control, combining low quiescent current, which results the output capacitor, the voltage on the VFB pin in high efficiency across a wide range of load currents. decreases. When this voltage falls 5mV below the Hysteresis using 800mV reference, the feedback comparator trips and Boundary Conduction Mode (BCM) to ramp the enables BCM. At the beginning of the BCM, the internal inductor current through the internal power switches, high-side power switch (P-channel MOSFET) is turned followed by a sleep cycle where the power switches are on and the inductor current begins to ramp up. The off and the load current is supplied by the output inductor current increases until either the current capacitor. During the sleep cycle, the RT6208 draws exceeds the peak current comparator threshold, or the only 25A of supply current. At light loads, the BCM ON time of the high-side MOSFET exceeds 5μs during cycles are a small percentage of the total cycle time the time VFB is higher than 800mV, at which the which minimizes the average supply current, greatly high-side power switch is turned off, and the Low-side improving efficiency. power switch is turned on. The inductor current ramps Mode operation functions by Scheme of Hysteresis Mode The feedback comparator monitors the voltage on the VFB pin and compares it to an internal 800mV reference, as shown in Figure 1. If this voltage is greater than the reference, the comparator activates a sleep mode in which the power switches and current Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6208-02 May 2016 down until the reverse current is close to zero. If the voltage on the VFB pin is still less than the 800mV reference, the high-side power switch is turned on again and another cycle commences which keep the inductor current operated in a boundary conduction mode. The average current during the BCM will normally be greater than the average load current. For is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT6208 this architecture, the maximum average output current to ground, the inductor current will decay very slowly is equal to half of the peak current. The hysteresis during a single switching cycle. Since the high-side nature of this control architecture results in a switching switch turns on only when the inductor current is near frequency that is a function of the input voltage, output zero, the RT6208 inherently switches at a lower voltage and inductor value. This behavior provides frequency during short-circuit condition. inherent short‑circuit protection. If the output is shorted VREF VFB VREF - VHys High-Side Peak Current (PC) Inductor Current Low-Side Zero Current (ZC) Sleep Mode Stop Switch Boundary Conduction Mode Sleep Mode Switch between High-Side PC and Low-Side ZC Figure 1. Hysteresis Mode Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS6208-02 May 2016 RT6208 Absolute Maximum Ratings (Note 1) Supply Voltage, VIN --------------------------------------------------------------------------------------------------- 0.3V to 40V Switch Voltage, SW ---------------------------------------------------------------------------------------------------- 0.3V to (VIN + 0.3V) <10ns ----------------------------------------------------------------------------------------------------------------------- 5V to 46.3V All Other Pins ------------------------------------------------------------------------------------------------------------ 0.3V to 6V Power Dissipation, PD @ TA = 25C SOT-23-6 ------------------------------------------------------------------------------------------------------------------ 0.48W SOT-23-8 ------------------------------------------------------------------------------------------------------------------ 0.53W Package Thermal Resistance (Note 2) SOT-23-6, JA ----------------------------------------------------------------------------------------------------------- 208.2C/W SOT-23-6, JC ----------------------------------------------------------------------------------------------------------- 32C/W SOT-23-8, JA ----------------------------------------------------------------------------------------------------------- 186.2C/W SOT-23-8, JC ----------------------------------------------------------------------------------------------------------- 47.4C/W Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------- 260C Junction Temperature ------------------------------------------------------------------------------------------------- 150C Storage Temperature Range --------------------------------------------------------------------------------------- 65C to 150C ESD Susceptibility (Note 3) HBM (Human Body Model) ----------------------------------------------------------------------------------------- 2kV MM (Machine Model) ------------------------------------------------------------------------------------------------- 200V Recommended Operating Conditions (Note 4) Input Voltage Range -------------------------------------------------------------------------------------------------- 4.75V to 36V Ambient Temperature Range -------------------------------------------------------------------------------------- 40C to 85C Junction Temperature Range -------------------------------------------------------------------------------------- 40C to 125C Electrical Characteristics (VIN = 12V, TA = 25C, unless otherwise specified) Parameter Supply Current Symbol Min Typ Max Unit Active Mode -- 160 190 A Sleep Mode -- 25 40 A VEN = 0V -- 3 6 A VFB Rising 0.792 0.8 0.808 V 3 5 7 mV 100 0 100 nA Shutdown Mode Test Conditions Feedback Comparator Trip Voltage VFB Feedback Comparator Hysteresis VFBHYS Feedback Pin Current IFB High-Side Switch On-Resistance RDS(ON)_H -- 3 -- Low-Side Switch On-Resistance RDS(ON)_L -- 1.5 -- 1 1.2 1.4 V -- 100 -- mV 3.9 4.2 4.75 V Enable Threshold Voltage Enable Rising Enable Hysteresis Input Under Voltage Lockout Threshold VUVLO Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6208-02 May 2016 VIN Rising is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT6208 Parameter Symbol Test Conditions Min Typ Max Unit Input Under Voltage Lockout Hysteresis ΔVUVLO -- 300 -- mV Soft-Start Period tSS -- 1 -- ms 200 225 250 500k from ISET to GND -- 135 -- ISET short to GND -- 50 -- Peak Current Comparator Propagation Delay Time ISET floating I/t = 250mA/s -- 100 -- ns Power Good Threshold - Rising VFB Rising -- 87.5 -- % Power Good Threshold - Falling VFB Falling -- 82.5 -- % -- 150 -- C ISET Floating High-Side Peak Current Limit Thermal Shutdown TSD mA 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. JA is measured at TA = 25C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. JC is measured at the lead of the package. Note 3. Devices are ESD sensitive. Handling precaution recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS6208-02 May 2016 RT6208 Typical Application Circuit L RT6208 VIN 4.75V to 36V SW VIN CIN VOUT R1 *CFF COUT FB EN (Open = automatic start) R2 ISET PGOOD GND AGND *See Application Information for detail. (Recommended Component Selections for a 100mA Loading application of Popular output Voltage) VOUT (V) CIN (F) COUT (F) L (H) R2 (k) R1 (k) CFF (pF) ISET 1.8 2.2 10 150 24 30 68 Floating 3.3 2.2 10 150 24 75 120 Floating 5 2.2 10 150 24 126 150 Floating Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6208-02 May 2016 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT6208 Typical Operating Characteristics Efficiency vs. Load Current 90 80 80 70 Efficiency (%) Efficiency (%) Efficiency vs. Load Current 90 VIN = 12V VIN = 24V 60 VIN = 36V 50 VIN = 12V 70 VIN = 24V VIN = 36V 60 50 VOUT = 3.3V VOUT = 1.8V 40 40 0.1 1 10 100 0.1 1 Load Current (mA) Efficiency vs. Load Current 90 157 Ground Current (μA) 160 Efficiency (%) 85 80 VIN = 12V 75 VIN = 24V VIN = 36V 65 60 154 151 148 145 142 139 136 133 VOUT = 5V 55 BCM 130 0.1 1 10 100 4 8 12 Load Current (mA) 190 27 180 24 Ground Current (μA) 30 170 160 VIN = 36V VIN = 24V 140 130 120 110 20 24 28 32 36 Ground Current vs. Input Voltage 200 150 16 Input Voltage (V) Ground Current vs. Temperature Ground Current (μA) 100 Ground Current vs. Input Voltage 95 70 10 Load Current (mA) Sleep Mode 21 18 15 12 9 6 Shutdown Mode 3 BCM 0 100 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 125 4 8 12 16 20 24 28 32 36 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. DS6208-02 May 2016 RT6208 Ground Current vs. Temperature UVLO vs. Temperature 50 4.6 VIN = 36V 40 High 4.4 Sleep Mode 35 UVLO (V) Ground Current (μA) 45 30 25 20 4.2 4.0 Low 15 Shutdown Mode 10 3.8 5 0 3.6 -50 -25 0 25 50 75 100 125 -50 -25 0 Temperature (°C) FB Voltage vs. Temperature 50 75 9 0.804 8 0.802 0.800 0.798 0.796 125 7 6 5 4 3 VIN = 24V, L = 100μH, C OUT = 10μF, Load = 30mA VIN = 24V 2 0.794 -50 -25 0 25 50 75 100 -50 125 -25 HS Peak Current Limit vs. Input Voltage 25 50 75 100 125 HS Peak Current Limit vs. Temperature 250 250 HS Peak Current Limit (mA) 225 ISET = Floating 200 175 150 125 ISET = 500kΩ 100 75 50 ISET = GND 25 0 225 ISET = Floating 200 175 150 125 ISET = 500kΩ 100 75 50 ISET = GND 25 VIN = 24V 0 4 8 12 16 20 24 28 32 Input Voltage (V) Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6208-02 0 Temperature (°C) Temperature (°C) HS Peak Current Limit (mA) 100 FB Voltage Hysteresis vs. Temperature 0.806 FB Voltage (mV) FB Voltage (V) 25 Temperature (°C) May 2016 36 -40 -10 20 50 80 110 140 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT6208 Switch On-Resistance vs. Temperature 5.0 4.5 4.5 Switch On-Resistance (Ω) Switch On-Resistance (Ω)1 Switch On-Resistance vs. Input Voltage 5.0 4.0 3.5 3.0 High-Side 2.5 2.0 1.5 1.0 Low-Side 4.0 3.5 3.0 High-Side 2.5 2.0 1.5 Low-Side 1.0 0.5 0.5 0.0 0.0 4 8 12 16 20 24 28 32 -50 36 -25 Switch Leakage Current vs. Temperature 25 50 75 100 125 EN Threshold Voltage vs. Temperature 0.1 1.4 0.09 EN Threshold Voltage (V) Switch Leakage Current (μA)1 0 Temperature (°C) Input Voltage (V) 0.08 0.07 0.06 0.05 0.04 0.03 0.02 1.3 Rising 1.2 1.1 Falling 1.0 0.9 0.01 VIN = 24V 0 0.8 -50 -25 0 25 50 75 100 125 -40 -10 20 50 80 Temperature (°C) Temperature (°C) Switching Soft-Start 110 140 VOUT_ac (20mV/Div) SW (20V/Div) Inductor Current (100mA/Div) VOUT (1V/Div) VIN = 24V, VOUT = 5V, ILOAD = 100mA Time (5s/Div) Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 VIN = 24V, VOUT = 5V Time (500s/Div) is a registered trademark of Richtek Technology Corporation. DS6208-02 May 2016 RT6208 Short Circuit Response Load Transient Respone VIN = 36V, VOUT = 5V, ILOAD = 100mA VIN = 24V, VOUT = 5V, ILOAD = 0 to 100mA VOUT_ac (50mV/Div) VOUT (2V/Div) Inductor Current (100mA/Div) Load Current (50mA/Div) Time (1ms/Div) Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6208-02 May 2016 Time (250s/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT6208 Application Information The typical RT6208 application circuit is shown on page 7 of this data sheet. External component R VOUT = VREF 1 + 1 R2 selection is determined by the maximum load current Where VREF is the reference voltage (0.8V typ.). requirement and begins with the selection of the peak The resistive divider attenuates the ripple signal on FB current programming resistor, RISET. The inductor pin as well. A small feed forward capacitor CFF can be value L can then be determined, followed by capacitors added in parallel with the upper feedback resistor R1. It CIN and COUT. helps to reduce switch-noise coupling on the FB pin Peak Current Resistor Selection The peak current comparator has a maximum current limit of 225mA nominally, which results in a maximum average current of 112mA. For applications that demand less current, the peak current threshold can be reduced to as little as 50mA. The threshold can be and increases the FB pin ripple voltage to improve switching stability and avoid double pulses. The CFF value is dependent on the feedback network impedance and the peak-peak ripple voltage on the output. Recommended CFF values range from 47pF to 470pF. easily programmed with an appropriately chosen Inductor Selection resistor (RISET) between the ISET pin and ground. The inductor, input voltage, output voltage and peak The value of resistor for a particular peak current can current determine the switching frequency of the be computed by following equation RT6208. For a given input voltage, output voltage and RISET = IPEAK 0.05 5.88 106 peak current, the inductor value sets the maximum where 50mA < IPEAK < 225mA. 1/2 of the peak current. A good first choice for the The peak current is internally limited to be within the inductor value can be determined by the following range of 50mA to 225mA. Shorting the ISET pin to equation : ground programs the current limit to 50mA, and leaving it floating sets the current limit to the maximum value of VOUT 1 VOUT L = VIN fMAX IPEAK 225mA. When selecting this resistor value, be aware The variation in switching frequency would be that the maximum average output current for this calculated with inductor, load current, input and output architecture is limited to half of the peak current. voltage. Large output capacitors will result in multiple Therefore, be sure to select a value that sets the peak switching cycles in BCM. The discharge time and current with enough margin to provide adequate load charge time of operation frequency can follow below current under all foreseeable operating conditions. equation : Output Voltage Setting and Feedback Network Discharge time (Sleep Mode) : T1 = C OUT The resistive divider allows the FB pin to sense the output voltage. The output voltage is set by an external resistive voltage divider according to the following switching frequency when the load current is close to VHys. ILOAD Charge time (Boundary Conduction Mode) : T2 = COUT 0.5 VHys. IPEAK ILOAD equation : Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS6208-02 May 2016 RT6208 Operation Frequency f = 1 T1 + T2 Input Under Voltage Lockout The RT6208 implements a protection feature which disables switching when the input voltage is too low. If VIN falls below 3.9V typical, an under voltage detector disables switching. Switching is enabled when the input voltage exceeds 4.2V typical (4.75V maximum). 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 output capacitor, COUT, filters the inductor’s ripple current and stores energy to satisfy the load current when the RT6208 is in sleep mode. The value of the output capacitor must be large enough to accept the energy stored in the inductor without a large change in Enable Operation output The EN pin can be used to shutdown or activate the peak-peak ripple less than 1% of the output voltage, chip. Pulling the EN pin low (<1V) will shutdown the the output capacitor must be : device. During shutdown mode, the RT6208 quiescent I COUT 50 L PEAK VOUT current drops to lower than 3A. Driving the EN pin high (>1.4V) will turn on the device again. Leaving the EN pin floating will pull the EN pin up to 2V internally and enable RT6208. voltage. To achieve an output voltage 2 Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power Soft-Start dissipation depends on the thermal resistance of the IC The RT6208 provides an internal soft-start function to package, PCB layout, rate of surrounding airflow, and prevent large inrush current and output voltage difference between junction and ambient temperature. overshoot when the converter starts up. The soft-start The maximum power dissipation can be calculated by automatically begins once the chip is enabled. During the following formula : soft-start, it clamps the ramp of internal reference PD(MAX) = (TJ(MAX) TA) / JA voltage which is compared with FB signal. The typical where TJ(MAX) is the maximum junction temperature, soft-start duration is 1ms. TA is the ambient temperature, and JA is the junction to ambient thermal resistance. CIN and COUT Selection For recommended operating condition specifications, The input capacitance, CIN, is needed to filter the triangular current at the Source of the high-side MOSFET. To prevent large ripple current, a low ESR input capacitor sized for the maximum RMS current should be used. The approximate RMS current equation is given : IRMS = IOUT(MAX) VOUT VIN IRMS = IOUT / 2. This simple worst case condition is commonly used for design because even significant Copyright © 2016 Richtek Technology Corporation. All rights reserved. May 2016 junction to ambient thermal resistance, JA, is layout dependent. For SOT-23-6 package, the thermal resistance, JA, is 208.2C/W on a standard JEDEC 51-7 four-layer thermal test board. For SOT-23-8 package, the thermal resistance, JA, is 186.2C/W on VIN 1 VOUT This formula has a maximum at VIN = 2VOUT, where DS6208-02 the maximum junction temperature is 125C. The a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25C can be calculated by the following formula : PD(MAX) = (125C 25C) / (208.2C/W) = 0.48W for SOT-23-6 package is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT6208 PD(MAX) = (125C 25C) / (186.2C/W) = 0.53W for SOT-23-8 package The maximum power dissipation depends on the operating ambient temperature for fixed TJ(MAX) and thermal resistance, JA. The derating curve in Figure 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Maximum Power Dissipation (W)1 1.0 Four-Layer PCB 0.9 0.8 0.7 SOT-23-8 0.6 0.5 0.4 SOT-23-6 0.3 0.2 0.1 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 2. Derating Curve of Maximum Power Dissipation Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS6208-02 May 2016 RT6208 Outline Dimension Symbol Dimensions In Millimeters Dimensions In Inches 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 Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6208-02 May 2016 is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT6208 Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 1.000 1.450 0.039 0.057 A1 0.000 0.150 0.000 0.006 B 1.500 1.700 0.059 0.067 b 0.220 0.500 0.009 0.020 C 2.600 3.000 0.102 0.118 D 2.800 3.000 0.110 0.118 e 0.585 0.715 0.023 0.028 H 0.100 0.220 0.004 0.009 L 0.300 0.600 0.012 0.024 SOT-23-8 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. Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 16 is a registered trademark of Richtek Technology Corporation. DS6208-02 May 2016