RT8402 RICHTEK | Alldatasheet
Document overview
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Technical content
Features
Built-In Power MOSFET Active Power Factor Correlation Programmable Constant LED Current with High-Precision Current Regulation Excellent Line And Load Regulation Suit For High Side Buck Low BOM Cost Requirement Unique Dimming Control Method to be compatible with TRIAC Dimmer Used in Low Input Voltage Range Support Low Percentage Dimming Angle Built-in Over Thermal Protection Output LED String Open Protection Output LED String Short Protection Over Current Protection
Applications
E27, PAR, Light Bar, Offline LED Lights Pin Configuration (TOP VIEW) VCC SGND GATE DIM VC SENSE 2 3 TSOT-23-6 Marking Information 2Q=DNN 2Q= : Product Code DNN : Date Code
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8402-00 January 2017 Simplified Application Circuit RT8402 Bootstrap diode R2A R2B DIM VCC SENSE GATESGND VC RG ZD1 Bridge Rectifier CIN Line Neutrl EC1 Functional Pin Description Pin No. Pin Name Pin Function 1 VCC Supply voltage input of the chip. For good bypass, a ceramic capacitor near the VCC pin is required. 2 SGND Ground of the chip. 3 GATE Gate driver for external MOSFET. 4 SENSE LED current sense input. 5 VC Close loop compensation node. 6 DIM Internal dimming function.
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8402-00 January 2017 www.richtek.com Functional Block Diagram GATE Regulator SGND DIM State Machine VCC VC AEA+ +- 250mV SENSE Duty Detection Operation The RT8402 senses the average output current and regulates the current precisely. The VC pin is the stability compensation node in this close loop. To stabilize the system and achieve better PFC / THDi, proper selection of a compensation network is needed. By using boundary mode control, it provides good efficiency performance. The dimming characteristic can be optimized by adjusting the external setting of DIM pin.
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8402-00 January 2017 Absolute Maximum Ratings (Note 1) Power Dissipation, PD @ TA = 25C Package Thermal Resistance (Note 2) ESD Susceptibility (Note 3) Recommended Operating Conditions (Note 4)
Electrical Characteristics
(VCC = 24V, TA = 25C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit VCC UVLO ON VUVLO_ON 17 18 19 V VCC UVLO OFF VUVLO_OFF 6 6.8 7.6 V VCC Shutdown Current ISD VCC = VUVLO_ON 3V -- -- 2 A VCC Operating Current ICC By CGATE = 1nF, VCC =24V VC =1V, SENSE = 0V 1.1 1.8 2.5 mA VCC 30V Operating Current ICC By CGATE = 1nF, VCC = 30V VC =1V, SENSE = 0V 2 2.7 3.4 mA VCC OVP Level VOVP 34.5 37 39.5 V VCC Clamp Level VCC_CLAMP -- 29 -- V VCC Clamp Current ICC_CLAMP -- 0.85 -- mA Sense Pin Leakage Current ISENSE VSENSE = 3V -- -- 2 A Current Sense Threshold VSENSE 240 250 260 mV DIM Pin Leakage Current IDIM VDIM = 5V -- -- 1 A GATE Voltage High VGATE_H IGATE = 0mA 10 12.5 15 V IGATE = 10mA 9 12 15
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8402-00 January 2017 www.richtek.com Parameter Symbol Test Conditions Min Typ Max Unit GATE Driver Rising Time tR CL = 1nF -- 80 -- ns Falling Time tF CL = 1nF -- 50 -- 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 under natural convection (still air) at T A = 25 C with the component mounted on a low effective-thermal-conductivity two-layer test board on a JEDEC thermal measurement standard. JC is measured at the exposed pad 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 © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. Figure 1. Typical Application of Buck Type
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8402-00 January 2017 www.richtek.com Typical Operating Characteristics Quiescent Current vs. Supply Voltage 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0 5 10 15 20 25 30 35 40 Supply Voltage (V) Quiescent Current (mA) VC = 0V Quiescent Current vs. Temperature 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -50 -25 0 25 50 75 100 125 Temperature (°C) Quiescent Current (mA) VC = 0V, VCC = 24V Operating Current vs. Supply Voltage 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 0 5 10 15 20 25 30 35 40 Supply Voltage (V) Operating Current (mA) GATE with 1nF, VC = 2V, SENSE = 0V Operating Current vs. Temperature 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -50 -25 0 25 50 75 100 125 Temperature (°C) Operating Current (mA) GATE with 1nF, VC = 2V, SENSE = 0V, VCC = 24V VCC Clamp Current vs. Temperature 0.70 0.75 0.80 0.85 0.90 0.95 1.00 -50 -25 0 25 50 75 100 125 Temperature (°C) VCC Clamp Currrent ( mA) OVP vs. Temperature -50 -25 0 25 50 75 100 125 Temperature (°C) VCC OVP ( V)
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8402-00 January 2017 UVLO vs. Temperature -50 -25 0 25 50 75 100 125 Temperature (°C) UVLO (V) UVLO_ON UVLO_OFF Sense Threshold vs. Supply Voltage 100 150 200 250 300 350 400 450 500 0 5 10 15 20 25 30 35 40 Supply Voltage (V) Sense Threshold (mV) Sense Threshold vs. Temperature 100 150 200 250 300 350 400 450 500 -50 -25 0 25 50 75 100 125 Temperature (°C) Sense Threshold (mV)
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8402-00 January 2017 www.richtek.com
Application Information
The RT8402 is a boundary mode, high efficiency constant current controller with internal high side driver, which can be used in buck configuration, to provide a constant output current to the (LED) load. It contains special circuitry for achieving high power factor and low input current THD, while minimizing external component count. The small SOT23 -6 package keeps application footprint small, and makes the RT8402 a cost effective solution for off-line LED drivers. The RT8402 can achieve high accuracy LED outpu t current via the average current feedback loop control. The internal sense voltage (250mV typ.) is used to set the average output current. The average current is set by the external resistor, RS. The sense voltage is also used for over current protection (OCP) function. The typical OCP threshold is about seven times of the sense voltage threshold. Under Voltage Lockout (UVLO) The RT8402 includes a UVLO function with 11.2V hysteresis. For system start up, the VIN must rise over 18V (typ.) to turn on the internal MOSFET. The internal MOSFET will turn off if VIN falls below 6.8V (typ.) Setting Average Output Current The output current that flows through the LED string is set by an external resistor, RS, which is connected between the SGND and SENSE pins. The relationship between output current, IOUT, and RS is shown below : OUT S 250I = mA R Start-up Resistor The start-up resistor should be chosen to set the start up current exceeds certain minimum value. Otherwise, the RT8402 may latch off and the system will never start. The start -up current equals 2 90V / R1 (for 110VAC regions), and equals 2 180V / R1 (for 220VAC regions). The typica l required minimum start-up current is 100 A. The typical t otal start up resistance (R1) is around 1M Ohm for universal inputs. Input Diode Bridge Rectifier Selection The current rating of the input bridge rectifier is dependent on the V OUT /VIN conversion ratio and out LED current. The voltage rating of the input bridge rectifier, VBR, on the other hand, is only dependent on the input voltage. Thus, the VBR rating is calculated as below : BR AC(MAX)V = 1.2 2 V 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, V BR will reach 448V. In this case, a 600V, 0.5A bridge rectifier can be chosen. Input Capacitor Selection For High Power Factor application, the input Capacitor CIN should use a small value capacitance to achieve line voltage sine-wave. The voltage rating of the input filter capacitor, V CIN, should be large enough to handle the input voltage. Thus, a 0.1 F / 500V film capacitor can be chosen in this case. Inductor Selection For high power factor application, the RT8402 operates the converter in BCM (Boundary-Condition Mode). The inductance range is defined by peak current of inductor、 maximum and minimum value of switching on time and off time, for ensuring the inductor operates in BCM. The peak current of inductor is showed as below : PEAK PEAK 2PinI = V F a OUT PEAK Vwhere a = V and a|0~0.7 The inductance range is showed as below :
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8402-00 January 2017 PEAK OUT ONOUT OFF PEAK PEAK V V TVTL = = II Where 0.5 s TON 35s (typ.) and 5 s TOFF 35s (typ.). The frequency at the top of the sine wave can be calculated : SW ON OFF DELAY 1f = T + T + T TDELAY is about 0.6s (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 : The input source is universal (V IN = 85V to 264V), V D will reach 448V. MOSFET Selection The peak current through this MOSFET will be over the maximum output current. This component current rating should be greater than 1.2 times the maximum load current and the reverse voltage rating of the MOSFET should be greater than 1.2 times the maximum input voltage, assuming a ±20% output current ripple. The peak voltage rating of the MOSFET is : The largest peak current will occur at the highest VIN. The current rating of MOSFET is determined by the OCP threshold which is about seven times of the sense voltage threshold. Thermal Protection (OTP) A thermal protection feature is included to protect the RT8402 from excessive heat damage. When the junction temperature exceeds a threshold of 150 °C (typ.), the thermal protection OTP will be triggered and the internal MOSFET will be turned off. Thermal Protection (OTP) A thermal protection feature is included to protect the RT8402 from excessive heat damage. When the junction temperature exceeds a threshold of 150°C (typ.), the thermal protection OTP will be triggered and the internal MOSFET will be turned off. Thermal Considerations The junction temperature should never exceed the absolute maximum junction temperature TJ(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. T he maximum power dissipation can be calculated using the following formula : PD(MAX) = (TJ(MAX) TA) / JA where T J(MAX) is the maximum junction temperature, TA is the ambient temperature, and JA is the junction-to-ambient thermal resistance. For continu ous operation, the maximum operating junction temperature indicated under Recommended Operating Conditions is 125C. The junction-to-ambient thermal resistance,JA, is highly package dependent. For a TSOT-23-6 package, the thermal resistance, JA, is 226.5C/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) = (125C 25C) / (226.5C/W) = 0.44W for a TSOT-23-6 package. The maximum power dissipation depends on the operating ambient temperature for the fixed T J(MAX) and the thermal resistance, JA. The derating curves in Figure 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation.
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8402-00 January 2017 Outline Dimension Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 1.000 0.028 0.039 A1 0.000 0.100 0.000 0.004 B 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 C 2.591 3.000 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 TSOT-23-6 Surface Mount Package
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8402-00 January 2017 www.richtek.com Footprint Information Package Number of Pin Footprint Dimension (mm) Tolerance P1 A B C D M 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 curre nt and complete. Ric htek 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 subsid iaries 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 su bsidiaries.