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Technical content
Features
Built-In 600V Power MOSFET Programmable Constant Output Voltage Extremely Low Quiescent Current Consumption and 1μμμμμA Shutdown Current Low System BOM Cost for Economical Step Down Converter Solution Universal Off-Line Input Voltage operation Range Built-In Over-Temperature Protection Built-In Over-Voltage Protection Output Open Protection Output Short Protection Output Over-Current Protection General Description The RT8409 integrates a power MOSFET controller. It is used for step down converters by well controlling the internal MOSFET and regulating a constant output voltage. The RT8409 features few system component counts and simple system design. Especially, the RT8409 can use a cheap simple drum core inductor in the system instead of an EE core while maintaining the high efficiency. The RT8409 is housed in a SOP-8 packag e. The components of the whole system can be made very compact.
Applications
Home Appliance Standby Power
Ordering Information
Note : Richtek products are : RoHS compliant and compatible with the current require- ments of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Package Type S : SOP-8 Lead Plating System G : Green (Halogen Free and Pb Free) RT8409 Pin Configuration (TOP VIEW) SOP-8 SGND COMP FB SENSE VCC NC DRAIN DRAIN 4 5 Marking Information RT8409 GSYMDNN RT8409GS : Product Number YMDNN : Date Code
DS8409-00 September 2016www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Functional Pin Description Pin No. Pin Name Pin Function 1 SGND Signal ground of the chip. 2 COMP Close loop compensation node. 3 FB Error amplifier input. 4 SENSE Current sense input. 5, 6 DRAIN Internal MOSFET drain. 7 NC No internal connection. 8 VCC Supply voltage input of the chip. For good bypass, a ceramic capacitor near the VCC pin is required. Typical Application Circuit SGND COMP FB RT8409 SENSE VCC C4D5 R2B R2A CIN VOUT DRAIN 5, 6 X X RSTART Bootstrap diode
DS8409-00 September 2016 www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Functional Block Diagram Operation The RT8409 senses the output voltage via the bootstrap loop. The output voltage feedback signal is compared to an internal reference voltage for the output voltage regulation. The COMP pin, which is the operational amplifier output node, is used for the control loop compensation to obtain stable response. To stabilize the system properly select the compensation network is required. The FB pin is the voltage loop input for the system regulation. The above COMP pin related compensation will be determined by specified system demand and be adapted to various applications. Burst Mode For the no load power saving demand, burst mode is a way to save power and maintain output regulation. High efficiency is achieved at light loads when Burst Mode operation is entered. The typical burst mode trigger levels are defined as follows. The MOSFET will stop switching when VC voltage goes lower tha n 200mV (typ.). The MOSFET will resume switching again once the VC voltage goes higher than 300mV (typ.). In this mode the output ripple has a variable frequency component that depends upon load current. Burst Mode operation ripple can be reduced slightly by using more output capacitance. VC VDS IOUT VC.high VC.low State Machine Regulator A VCC DRAIN SGND SENSE COMP FB 1.75V EA
DS8409-00 September 2016www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation.
Electrical Characteristics
Parameter Symbol Test Conditions Min Typ Max Unit VCC UVLO ON V UVLO_ON 17 18 19 V VCC UVLO OFF V UVLO_OFF 6.5 7 8 V VCC Shutdown Current I SD V CC = VUVLO_ON 3V -- 1.5 3 A VCC Quiescent Current I QC Gate stands still -- 0.5 2 mA VCC Operating Current I CC By C GATE = 1nF, Freq.= 20kHz -- 1 2 mA VCC OVP Level V CC_OVP 23.75 25 26.25 V Current Sense Threshold V SENSE 0.97 1.04 1.11 V Sense Pin Leakage Current I SENSE V SENSE = 3V -- 1 5 A FB Pin Threshold V FB 1.7 1.75 1.8 V FB Over Voltage Protection V FB_OVP 1.82 1.96 2.1 V FB Pin Leakage Current I FB V FB = 5V -- 1 3 A Switch Off Time t OFF 18 25 32 s Static Drain-Source On-Resistance RDS(ON) V GD = 12V, ID = 50mA -- 6 -- Drain-Source Leakage Current IDSS V DS = 600V -- -- 10 A Recommended Operating Conditions (Note 4) Absolute Maximum Ratings (Note 1) Power Dissipation, PD @ TA = 25°C Package Thermal Resistance (Note 2) ESD Susceptibility (Note 3) (VCC = 15V, T A = 25°C, unless otherwise specified)
DS8409-00 September 2016 www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. 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. θ JA is measured under natural convection (still air) at TA = 25°C with the component mounted on a low effective-thermal- conductivity two-layer test board on a JEDEC 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.
DS8409-00 September 2016www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Sense Threshold vs. Supply Votatge 0.8 0.9 0.9 1.0 1.0 1.1 1.1 1.2 1.2 10 12 14 16 18 20 22 Supply Voltage (V) Sense Threshold (V) VCC OVP vs. Temperature - 5 0- 2 5 0 2 5 5 0 7 51 0 0 1 2 5 Temperature (°C) VCC OVP (V) Operating Current vs. Supply Voltage 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 8 1 01 21 41 61 82 02 2 Supply Voltage (V) Operating Current (mA) Standby Power 100 90 110 130 150 170 190 210 230 250 270 Input AC Voltage (VAC) Input Power (mW) Typical Operating Characteristics VOUT = 15V, no Load, start-up resistor = 2M Ω UVLO vs. Temperature - 5 0- 2 5 0 2 5 5 0 7 51 0 0 1 2 5 Temperature (°C) UVLO (V) UVLO_ON UVLO_OFF Operating Current vs. Temperature 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 -50 -25 0 25 50 75 100 125 Temperature (°C) Operating Current (mA) VCC = 15V
DS8409-00 September 2016 www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. FB OVP vs. Supply Voltage 1.88 1.90 1.92 1.94 1.96 1.98 2.00 2.02 2.04 2.06 2.08 2.10 10 12 14 16 18 20 22 Supply Voltage (V) FB OVP (V) FB Voltage vs. Supply Voltage 1.70 1.72 1.74 1.76 1.78 1.80 10 12 14 16 18 20 22 Supply Voltage (V) FB Voltage (V) FB Voltage vs. Temperature 1.66 1.68 1.70 1.72 1.74 1.76 1.78 1.80 1.82 1.84 1.86 - 5 0- 2 5 0 2 5 5 0 7 51 0 0 1 2 5 Temperature (°C) FB Voltage (V) VCC = 15V FB OVP vs. Temperature 1.80 1.84 1.88 1.92 1.96 2.00 2.04 2.08 2.12 2.16 2.20 - 5 0- 2 5 0 2 5 5 0 7 51 0 0 1 2 5 Temperature (°C) FB OVP (V) VCC = 15V Sense Threshold vs. Temperature 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 - 5 0- 2 5 0 2 5 5 0 7 51 0 0 1 2 5 Temperature (°C) Sense Voltage (V) VCC = 15V
DS8409-00 September 2016www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. Applications Information The RT8409 is a constant off time control, high efficiency constant voltage high side converter with internal MOSFET. It can be used in buck down solution, to provide a constant output voltage to the load. It contains high side bootstrap voltage sense circuitry, while minimizing external component count. The SOP8 package keeps application footprint small, and makes the RT8409 a cost effective solution for off-line buck converter. The RT8409 can achieve high accuracy output voltage via FB pin, which is the average output voltage sense feedback loop control pin. The internal FB reference voltage (1.75V typ.) is used to set the average output voltage by the external resistor, R2A, R2B. The sense voltage from sense pin is used for Over Current Protection (OCP) function. Under-Voltage Lockout (UVLO) The RT8409 includes a UVLO function with 11V hysteresis. For system start up, the VCC must rise over 18V (typ.) to turn on the internal MOSFET. The internal MOSFET will be turned off if VCC falls below 7V (typ.) Setting Average Output Voltage The output voltage that provides to the output load is set by external resistors, R2A, R2B, which is connected between the cathode of D7 and SGND pins. The relationship between output voltage, and R2A, R2B is shown below : Start-Up Resistor The start-up resistor should be chosen to set the start up current exceeds certain minimum value. Otherwise, the RT8409 may latch off and the system will never start. The start-up current equals where 90V is assumed the minimum line input voltage. The typical required minimum start-up current is 60 μA. The recommended total start-up resistance R START for universal inputs should be no more than 2MΩ. 2A 2BOUT F_D7 F_D5 R + RV = 1.75V + V - VR START 29 0 V R Input Diode Bridge Rectifier Selection The voltage rating of the input bridge rectifier, VBR, dependent on the input voltage. Thus, the VBR rating is calculated as below : where VAC(MAX) is the maximum input voltage (RMS) and the parameter 1.2 is used for safety margin. For this example : If the input source is universal, VBR will reach 448V. In this case, a 600V, 0.5A bridge rectifier can be chosen. Inductor Selection For best efficiency, the RT8409 should be operated near boundary conduction mode. Based on this recommendation, the required inductor value is related to the input voltage, output voltages, the min. on-time and the max. off time. The inductor saturation current will be related to the over current limit set by the sense resistor between the sense pin and ground pin. The over current limit design information can be found in the later section. The peak current of inductor is showed as below : IN OUTPEAK ON VVI = t L SW OUT IN V V V + VL 2 f I V 2ba c bOFF_1 a OUT INa IN OUT OUT OUTb IN OUT OUT OFF K + K + 4 K K t = 2 K V VK = L V V V IK = V V Kc = I t Where VOUT is output voltage. VIN is input voltage. IOUT is full load current. OUTON OFF_1 IN OUT Vt = t V V
DS8409-00 September 2016 www.richtek.com ©Copyright 2016 Richtek Technology Corporation. All rights reserved. is a registered trademark of Ric htek Technology Corporation. The input source is universal (VIN = 90V to 264V), VD will reach 448V. Bootstrap Diode Selection The bootstrap diode is connected the switch output to provide supply voltage for VCC, and output voltage for FB divided resistors. The reverse voltage rating of the diode should be greater than maximum input voltage. A fast diode can be used, such as ES1J or FR107. Sense Resistor Selection The resistor, R5, between the Source of the external N- MOSFET and SGND should be selected to provide adequate switch current to drive the application without exceeding the current limit threshold set by the SENSE pin sense threshold of the RT8409. The Sense resistor value can be calculated according to the formula below : fSW is switching frequency from 30kHz to 55kHz. tOFF is constant off time (25μs, Typ.). Forward 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 minimum voltage drop and recovery time. The reverse voltage rating of the diode should be greater than the maximum input voltage and the current rating should be greater than the maximum load current. The peak voltage stress of diode is : CLT OCP VR2 I where VCTL is the current limit threshold (0.97V, min.). IOCP is about 1.2 to 1.5 times of the peak inductor current. Thermal Protection (OTP) A thermal protection feature is included to protect the RT8409 from excessive heat damage. When the junction temperature exceeds a threshold of 150°C, the thermal protection OTP will be triggered and the RT8409 will be turned off. Thermal Considerations The junction temperature should never exceed the absolute maximum junction temperature T J(MAX), listed under Absolute Maximum Ratings, to avoid permanent damage to the device. The maximum allowable power dissipation depends on the thermal resistance of the IC package, the PCB layout, the rate of surrounding airflow, and the difference between the junction and ambient temperatures. The maximum power dissipation can be calculated using the following formula : P D(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 continuous operation, the maximum operating junction temperature indicated under Recommended Operating Conditions is 125 °C. The junction-to-ambient thermal resistance, θ JA, is highly package dependent. For a SOP-8 package, the thermal resistance, θJA, is 206.9°C/W on a standard JEDEC low effective-thermal- conductivity two-layer test board. The maximum power dissipation at T A = 25°C can be calculated as below : PD(MAX) = (125°C − 25°C) / (206.9 °C/W) = 0.48W for a SOP-8 package. The maximum power dissipation depends on the operating ambient temperature for the fixed TJ(MAX) and the thermal resistance, θJA. The derating curves in Figure 1 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation.
DS8409-00 September 2016 www.richtek.com 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 ci rcuitry entirely embodied in a Richtek product. Information furnish ed by Richtek is believed to be accurate and reliable. However, no respon sibility is assumed by Richtek or its subsidiaries for its use; nor for any infringeme nts 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 R ichtek or its subsidiaries. Outline Dimension A BJ F H M C D I 8-Lead SOP Plastic Package Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 4.801 5.004 0.189 0.197 B 3.810 3.988 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.508 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.170 0.254 0.007 0.010 I 0.050 0.254 0.002 0.010 J 5.791 6.200 0.228 0.244 M 0.400 1.270 0.016 0.050