RT8487 RICHTEK | Alldatasheet
Document overview
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Technical content
Features
Support High Power Factor and THDi Consideration Applications Programmable Constant LED Current with Highly Precision Current Regulation Extremely Low Quiescent Current Consumption and 1µA Shutdown Current True Low System BOM Cost and Economical Floating Buck Converter Solution Unique Programmable AND Pin for ZVS Se tting to Achieve Best Power Efficiency Universal Input Voltage Range with Off -Line Topology Built-in Over Thermal Protection Built-in Over Voltage Protection Output LED String Open Protection Output LED String Short Protection Output LED String Over Current Protection
Applications
E27, PAR, Light Bar, Offline LED Lights Pin Configurations (TOP VIEW) VCC GND GATE SENSE VC AND 2 3 TSOT-23-6
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8487-00 March 2015 Simplified Application Circuit Buck type: COUT Bootstrap Diode RS Bridge Rectifier CIN R3B AND VCC GATE SENSEGND VC RT8487
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8487-00 March 2015 www.richtek.com Functional Pin Description Pin No. Pin Name Pin Function 1 VCC Supply Voltage Input. For good bypass, a ceramic capacitor near the VCC pin is required. 2 GND Ground. 3 GATE Gate Driver Output for External MOSFET Switch. 4 AND AND Function Pin. 5 VC Close Loop Compensation Node. 6 SENSE LED Current Sense Input. The typical sensing threshold is 250mV between the SENSE and GND pin. Function Block Diagram State Machine Regulator A V VCC GATE GND ANDVC SENSE 250mV EA Operation The RT8487 senses true average output current and keeps the system driving constant output current. The VC pin is the compensation node in this close loop system and dominate s the frequency response. To stabilize the system and achieve better PFC / THDi, proper selection of a compensation network is needed.
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8487-00 March 2015 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 6.4 7.2 8 V VCC Shutdown Current ISD VCC = VUVLO_ON 3V -- -- 1 A VCC Quiescent Current IQC Gate stands still -- 0.5 5 mA VCC Operating Current ICC By CGATE = 1nF, Freq.= 20kHz -- 1 5 mA VCC OVP Level VOVP -- 34 -- V Sense Pin Leakage Current ISENSE VSENSE = 3V -- 1 5 A Current Sense Threshold VSENSE 242.5 250 257.5 mV AND Pin Leakage Current IAND VAND = 5V -- 1 2 A GATE Voltage High VGATE_H IGATE = 0mA 10.5 12 -- V IGATE = 10mA 9 10 -- GATE Driver Rising Time tr -- 50 -- ns Falling Time tf -- 25 -- 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. Note 3. Devices are ESD sensitive. Handling precaution recommended. Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8487-00 March 2015 www.richtek.com Typical Application Circuit Buck : COUT RS1M RS Bridge Rectifier CIN R3B AND VCC GATE SENSEGND VC RB 470μH0.8 ES2J 270μF/63V MTN4N60 511K 511K 0.1μF/500V 100k 1μF4.7μF/50V RT8487
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8487-00 March 2015 Typical Operating Characteristics Operating 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 10 20 30 40 Supply Voltage (V) Operating Current (mA) GATE with 1nF 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) VCC = 24V, GATE with 1nF OVP vs. Temperature -50 -25 0 25 50 75 100 125 Temperature (°C) OVP (V) 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 10 20 30 40 Supply Voltage (V) Sense Threshold (mV) Sense Threshold vs. Temperature 100 150 200 250 300 350 400 450 500 -50 0 50 100 150 Temperature (°C) Sense Threshold (mV) VCC = 24V
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8487-00 March 2015 www.richtek.com Efficiency vs. Input Voltage 100 85 105 125 145 165 185 205 225 245 265 Input Voltage (V) Efficiency (%) VIN_AC = 90V to 264V IOUT = 300mA, LED 14pcs, L = 470μH Output Current vs. Input Voltage 250 260 270 280 290 300 310 320 330 340 350 85 105 125 145 165 185 205 225 245 265 Input Voltage (V) Output Current (mA) VIN_AC = 90V to 264V IOUT = 300mA, LED 14pcs, L = 470μH Power Factor vs. Input Voltage 0.70 0.75 0.80 0.85 0.90 0.95 1.00 85 105 125 145 165 185 205 225 245 265 Input Voltage (V) Power Factor VIN_AC = 90V to 264V IOUT = 300mA, LED 14pcs, L = 470μH VIN_AC = 264V Input and Output Current Time (5ms/Div) VIN (500V/Div) VOUT (50V/Div) IIN (200mA/Div) IOUT (500mA/Div) IOUT = 300mA, LED 14pcs, L = 470μH Power On Time (100ms/Div) VIN (500V/Div) VOUT (20V/Div) IOUT (200mA/Div) VIN_AC = 264V IOUT = 300mA, LED 14pcs, L = 470μH Power Off Time (100ms/Div) VIN (500V/Div VOUT (20V/Div) IOUT (200mA/Div) VIN_AC = 264V IOUT = 300mA, LED 14pcs, L = 470μH
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8487-00 March 2015 Total Harmonic Distortion 10% 15% 20% 25% 30% 35% 40% 45% 50% 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 Class C Measured VIN_AC = 115V/60Hz IOUT = 300mA, LED 14pcs, L = 470μH Total Harmonic Distortion 10% 15% 20% 25% 30% 35% 40% 45% 50% 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 VIN_AC = 230V/50Hz IOUT = 300mA, LED 14pcs, L = 470μH Class C Measured
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8487-00 March 2015 www.richtek.com
Application Information
RT8487 is a boundary mode, high efficiency constant current controller with internal high side driver, which can be used in buck and buck -boost 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 RT8487 a cost effective solution for off -line LED drivers. The R T8487 can achieve high accuracy LED output current via the average current feedback loop control. The internal sense voltage (250mV typ.) is used to set the average output curr ent. The average current is set by the external resistor, RS. The sense voltag e 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 RT8487 includes a UVLO function with 10.8V hysteresis. For system start up, the VIN must rise over 18V (typ.) to turn on the GATE terminal. The GATE terminal will turn off if VIN falls below 7 .2V (typ.) Setting Average Output Current The output current that flows through the LED string is set by an external resistor, RS, which is connecte d between the GND 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 RT8487 may latch off and the system will never start. The start-up current equals (for 110VAC regions), and equals (for 220VAC regions). The typical required minimum start-up current is 100 A. The typical total start up resistance (R1 + R2) 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, VBR 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, VCIN, should be large enough to handle the input voltage.
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS8487-00 March 2015 Thus, a 0.1 F / 500V film capacitor can be chosen in this case. Inductor Selection For high power factor application, the RT8487 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 : PEAK OUT ONOUT OFF PEAK PEAK V V TVTL = = II Where 0.5s TON 35s and 2s TOFF 30s The frequency at the top of the sine wave can be calculated : SW ON OFF DELAY 1f = T + T + T (TDELAY is determined by the resistor connected to AND pin , see Turn on delay time) Turn On Delay Time After the inductor current has reached zero, a resonance will occur between the inductor and the MOSFET drain-source capacitance. In order to minimize the MOSFET switching losses, RT8487 provides the flexibility to adjust the delay time of next switch -on cycle in order to switch -on at the maximum point of the resonance, which corresponds to the minimum drain-source voltage value. The delay time from zero current point to the maximum of the switch resonance which can be calculated from : resonance SWT = L1 C where C SW is the capacitance at the switch node, mostly determined by the MOSFET drain -source capacitance. The delay time TDELAY from zero current detection point to next MOSFET switch-on cycle can be adjusted by the resistor value R3B connected between AND pin and IC GND TDELAY(μs)=(-0.4 x R3B2+3500 x R3B+407500) x 10-6 R3B resister value in k. 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 shou ld 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 V IN. The current rating of MOSFET is determined by the
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. difference between junction and ambient temperature. temperature on the maximum power dissipation. Figure 1. Derating Curve of Maximum Power layout guidelines should be strictly followed.
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. Figure 2. PCB Layout Guide
Copyright © 2015 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS8487-00 March 2015 www.richtek.com 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 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.