RT8458AGJ6

® RT8458A High Efficiency PWM Buck LED Driver Controller General Description Features The RT8458A is a PWM controller with an integrated high side gate driver. It is used for step down converters by well controlling the external MOSFET and regulating a constant output current. The output duty cycle of the RT8458A can be up to 100% for wider input voltage application, such as E27 and PAR30 off-line LED lighting products.  Low Cost and Efficient Buck Converter Solution  Universal Input Voltage Range with Off-Line Topology Programmable Constant LED Current Dimmable LED Current by ACTL Output LED String Open Protection Output LED String Short Protection Output LED String Over Current Protection Built-in Thermal Protection TSOT-23-6 Package RoHS Compliant and Halogen Free The RT8458A also features a 47kHz fixed frequency oscillator, an internal −220mV precision reference, and a PWM comparator with latching logic. The accurate output LED current is achieved by an averaging current feedback loop and the LED current dimming can be easily controlled via the ACTL pin. The RT8458A also has multiple features to protect the controller from fault conditions, including Under Voltage Lockout (UVLO), Over Current Protection (OCP) and Over Voltage Protection (OVP). Additionally, to ensure the system reliability, the RT8458A is built with the thermal protection function.         Applications  E27, PAR30, Offline LED Lights Marking Information 07= : Product Code 07=DNN DNN : Date Code The RT8458A is housed in a TSOT-23-6 package. Thus, the components in the whole LED driver system can be made very compact. Simplified Application Circuit VIN CIN RVCC1 RVCC2 D2 RT8458A VCC ACTL CVCC VC CVC2 RVC GND CVC1 Analog Dimming GATE Q1 SENSE RS D1 L1 LED+ COUT LED- Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8458A-09 August 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8458A Ordering Information Pin Configurations RT8458A (TOP VIEW) Package Type J6 : TSOT-23-6 SENSE VC ACTL Lead Plating System G : Green (Halogen Free and Pb Free) 6 Note : 4 2 3 VCC GND GATE Richtek products are :  5 TSOT-23-6 RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.  Suitable for use in SnPb or Pb-free soldering processes. 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 GND Ground of the Chip. 3 GATE Gate Driver Output for External MOSFET Switch. 4 ACTL Analog Dimming Control Input. The effective dimming range is between 0.1V to 1.2V. If VACTL is greater than 1.2V, the ACTL dimming signal high is internally clamped around 1.3V. If dimming is not used, a pull up resistor or a voltage holding capacitor between ACTL and GND pins should be used. 5 VC PWM Loop Compensation Node. 6 SENSE LED Current Sense Input. The Typical sensing threshold is 220mV between the SENSE and GND pin. Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8458A-09 August 2014 RT8458A Function Block Diagram + + 17V/8V OVP + - VCC 35V VREF Chip Enable 47kHz OSC 12V S GATE R 200k R CCOMP GND + - Control Circuit VC SENSE - OTP OP1 + -220mV Dimming ACTL Operation The RT8458A is a Buck PWM current mode controller with an integrated high side gate driver. The start up voltage of RT8458A is around 17V. Once VCC is above 17V, RT8458A will maintain operation until VCC drops below 8V. The RT8458A's main control loop consists of a 47kHz fixed frequency oscillator, an internal −220mV precision current sense threshold OPAMP (OP1), and a PWM comparator (CCOMP) with latching logic. In normal operation, the GATE turns high when the gate driver is set by the oscillator (OSC). The lower the average of the sensed current is below the loop-regulated −220mV threshold, the higher the VC pin voltage (OP1 output) will go high. Higher the VC voltage means longer the GATE turn-on period. The GATE of RT8458A can turn on more than 100% duty. It is not always that the GATE turns low Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8458A-09 August 2014 in each OSC cycle. The GATE turns low until the current comparator (CCOMP) resets the gate driver. The GATE will be set high again by OSC and the next switching cycle repeats. The adjustment of the regulated sense current threshold (dimming) can be achieved by varying ACTL pin voltage. The typical range of ACTL voltage adjustment is between 0.1V and 1.2V. The RT8458A is equipped with protection from several fault conditions, including input voltage Under Voltage Lockout (UVLO), Over Current Protection (OCP) and VIN/VOUT Over Voltage Protection (OVP). Additionally, to ensure the system reliability, the RT8458A is built with internal thermal protection function. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8458A Absolute Maximum Ratings            (Note 1) Supply Input Voltage, VCC ---------------------------------------------------------------------------------------------GATE Voltage (Note 8) ------------------------------------------------------------------------------------------------ACTL Voltage (Note 6) ------------------------------------------------------------------------------------------------VC Voltage -----------------------------------------------------------------------------------------------------------------SENSE Voltage -----------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C TSOT-23-6 ------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) TSOT-23-6, θJA ------------------------------------------------------------------------------------------------------------TSOT-23-6, θJC ------------------------------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------------------- Recommended Operating Conditions   −0.3V to 40V −0.3V to 17V −0.3V to 8V −0.3V to 6V −1V to 0.3V 0.392W 255°C/W 135°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VCC ---------------------------------------------------------------------------------------------- 17V to 31V Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Electrical Characteristics (VCC = 24VDC, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Input Start-Up Voltage VST Minimum Operation Voltage VIN(MIN) After Start-Up Input Supply Current ICC Maximum ICC to cause VCC stop hiccup at low end of VCC hysteresis level After Start-Up, VCC = 24V Input Shutdown Current IQC Before Start-Up, VCC = 5V Maximum Startup Current in IST(MAX) VCC Hiccup Operation Min Typ Max Unit -- 17 19 V -- 8 9 V -- 250 300 A -- 2 5 mA -- 1 5 A 38 47 56 kHz -- -- 100 % -- 97 -- % Oscillator Switching Frequency Maximum Duty in Transient Operation Maximum Duty in Steady State Operation Blanking Time f SW tBLANK (Note 7) -- 300 -- ns Minimum Off Time tOff(MIN) (Note 7) -- 600 -- ns DMAX(TR) VC = 3V DMAX Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8458A-09 August 2014 RT8458A Parameter Symbol Test Conditions Min Typ Max Unit Current Sense Amplifier Current Sense Voltage VSENSE (Note 5) 213 220 227 mV Sense Input Current ISENSE (Note 7) -- 11 -- A VC Sourcing Current IVC_Source VSENSE = 150mV (Note 7) -- 20 -- A VC Sinking Current IVC_Sink VSENSE = 250mV (Note 7) -- 180 -- A 1.15 1.25 1.35 V -- 12.6 16 V IGATE = 50mA 10.5 12.1 14 IGATE = 100A -- 12.5 -- IGATE = 50mA 0.01 0.75 1.2 IGATE = 100A -- 0.5 -- GATE Drive Rise Time 1nF Load at GATE -- 60 150 ns GATE Driver Fall Time 1nF Load at GATE -- 30 100 ns GATE Drive Source Peak Current 1nF Load at GATE -- 0.25 0.5 A GATE Driver Sink Peak Current 1nF Load at GATE -- 0.5 0.8 A VACTL = 1.2V -- 1 5 A VACTL_On -- 1.2 1.3 V VACTL_Off -- 0.1 0.2 V 32 35 38 V -- 150 -- C VC Threshold for PWM Switch Off VVC GATE Driver Output GATE Pin Maximum Voltage VGATE GATE Voltage High VGATE_H GATE Voltage Low VGATE_L No Load at GATE Pin V V LED Dimming Analog Dimming ACTL Pin Input Current LED Current On Threshold at ACTL LED Current Off Threshold at ACTL IACTL OVP Over Voltage Protection VOVP VCC Pin Thermal Protection Thermal Shutdown Temperature TSD 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 low effective thermal conductivity single-layer test board per JEDEC 51-3. θJC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. The RT8458A achieves precise LED average current with a current feedback loop to sense the average LED current, in the deep discontinuous mode operation especially when a small inductor is used small current offset might occur due to current waveform distortion of the nature of the discontinuous operation. This offset current is consistent over production. Note 6. If a 1MΩ resistor is connected between the control input and ACTL pin, the control input voltage can be up to 36V. Note 7. Guaranteed by design, not subjected to production test. Note 8. The GATE voltage is internally clamped and varies with operating conditions. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8458A-09 August 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8458A Typical Application Circuit VIN VMAIN CIN 10µF/ 400V RVCC1 1M RVCC2 511k RT8458A 1 VCC ACTL 4 CVCC 4.7µF CVC2 3.3nF RVC 10k CVC1 1nF 5 VC 2 GND GATE 3 RACTL 1M RG 22R Q1 ZD1 short Optional Optional SENSE 6 VIN_AC : 85V to 264V VOUT : 30V IOUT : 350mA Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 D2 FR107 RB 10 Optional D1 ES1J RS 0.63 L1 680µH LED+ COUT 220µF/50V ZD2 39V Optional LED- is a registered trademark of Richtek Technology Corporation. DS8458A-09 August 2014 RT8458A Typical Operating Characteristics Efficiency vs. Input Voltage Efficiency vs. Number of LED 100 100% 100% 100 10LED 9LED 8LED 7LED 95 95% 90% 90 Efficiency (%) Efficiency (%) 95 95% 85% 85 80% 80 6LED 5LED 4LED 3LED 75% 75 85 105 125 145 165 185 205 225 245 90 90% 85% 85 80% 80 75% 75 VIN_AC = 85V to 264V, IOUT = 350mA, LED3 to LED10 pcs 70% 70 85VAC 110VAC 150VAC 180VAC 220VAC 264VAC VIN_AC = 85V to 264V, IOUT = 350mA, LED3 to LED10 pcs 70% 70 265 3 4 5 Input Voltage (V) 6 7 8 9 10 Number of LED (pcs) LED Current vs. Output Voltage LED Current vs. Input Voltage 400 400 350 LED Current (mA) LED Current (mA) 380 360 340 320 IOUT = 350mA (L = 0.68mH) 300 250 IOUT = 250mA (L = 1.5mH) 200 150 100 IOUT = 100mA (L = 3.3mH) 50 VIN_AC = 110V, IOUT = 350mA, LED3 to LED10 pcs VIN_AC = 85V to 264V, LED10 pcs 0 300 0 4 8 12 16 20 24 28 32 85 36 105 125 145 Output Voltage (V) SENSE Threshold vs. Input Voltage 185 205 225 245 265 SENSE Threshold vs. Temperature 230 220 218 IOUT = 350mA (L = 0.68mH) 216 214 IOUT = 250mA (L = 1.5mH) 212 210 208 IOUT = 100mA (L = 3.3mH) 206 204 202 SENSE Threshold (mV) SENSE Threshold (mV) 165 Input Voltage (V) 225 220 215 210 205 VIN_AC = 85V to 264V, LED10 pcs 200 200 85 105 125 145 165 185 205 225 245 Input Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8458A-09 August 2014 265 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8458A Switching Frequency vs. VCC Switching Frequency vs. Temperature 55 Switching Frequency (kHz)1 Switching Frequency (kHz)1 55 51 47 43 39 35 51 47 43 39 35 0 4 8 12 16 20 24 28 32 36 -50 VCC (V) -25 0 25 50 75 100 125 Temperature (°C) SENSE Threshold vs. ACTL Voltage Input and Output Current SENSE Threshold (mV) 250 VIN (400V/Div) 200 150 I IN (1A/Div) 100 VOUT (50V/Div) IOUT (500mA/Div) 50 VIN_AC = 264V, IOUT = 350mA, LED 10 pcs, L = 0.68mH 0 0 0.5 1 1.5 2 2.5 3 Time (25ms/Div) ACTL Voltage (V) Power On Power Off VIN (400V/Div) VIN (400V/Div) VOUT (20V/Div) VOUT (20V/Div) IOUT (500mA/Div) VIN = 264VAC, IOUT = 350mA, LED 10 pcs, L = 0.68mH Time (25ms/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 IOUT (500mA/Div) VIN = 264VAC, IOUT = 350mA, LED 10 pcs, L = 0.68mH Time (25ms/Div) is a registered trademark of Richtek Technology Corporation. DS8458A-09 August 2014 RT8458A Application Information The RT8458A is a high efficiency PWM Buck LED driver controller for high brightness LED application. Its high side floating gate driver is used to control the Buck converter via an external MOSFET and regulate the constant output current. The RT8458A can achieve high accuracy LED output current via the average current feedback loop control. The internal sense voltage (−220mV typ.) is used to set the average output current. The oscillator’s frequency is fixed at 47kHz to get better switching performance. Once the average current is set by the external resistor, RS, the output LED current can be dimmed by varying the ACTL voltage. Under Voltage Lockout (UVLO) The RT8458A includes a UVLO feature with 9V hysteresis. The GATE terminal turns on when VIN rises over 17V (typ.). The GATE terminal turns off when VIN falls below 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 GND and SENSE pins. With ACTL pin voltage greater than 1.2V, the relationship between output current, IOUT, and RS is shown below : 0.22 IOUT = (A) RS Analog Dimming Control The ACTL terminal is driven by an external voltage, VACTL, to adjust the output current to an average value set by RS. The voltage range for VACTL to adjust the output current is from 0.1V to 1.2V. For VACTL between 0.1V to 1.2V, the output current value will be determined by the following formula : V  0.1 IOUTavg = (0.22V/RS )  ACTL 1.1 Component Selection For component selection, an example is shown below for a typical RT8458A application, where VIN = 110 to 90VAC/ 60Hz, LED output voltage = 30V, and output current = 200mA. The user can follow this procedure to design applications with wider AC voltage input and DC output voltage as well. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8458A-09 August 2014 Start-up Resistor Start-up resistor should be chosen not to exceed the maximum start-up current. Otherwise, the RT8458A may latch low and will never start. Start-up current = 130V/R1 for 110VAC regions, 260V/R1 for 220VAC regions. The typical start-up current is 250μA. Input Diode Bridge Rectifier Selection The current rating of the input bridge rectifier is dependent on the VOUT /VIN transformation ratio. 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 : VBR = 1.2  ( 2  VAC(MAX) ) where VAC,Max is the maximum input voltage (RMS) and the parameter 1.2 is used for safety margin. For this example : VBR = 1.2  ( 2  VAC(MAX) ) = (1.2  2  110) = 187V 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 The input capacitor supplies the peak current to the inductor and flattens the current ripple on the input. The low ESR condition is required to avoid increasing power loss. The ceramic capacitor is recommended due to its excellent high frequency characteristic and low ESR. For maximum stability over the entire operating temperature range, capacitors with better dielectric are suggested. The minimum capacitor is given by : VOUT(MAX)  IOUT(MAX) CIN  ( 2  VAC(MIN) )2  V 2DC(MIN)    fAC   where fAC is the AC input source frequency and η is the efficiency of the whole system. Notice that VDC(MIN) is the minimum voltage at bridge rectifier, output and VDC(MIN) should be larger than 2 x VOUT(MAX). For a 90 to 264VAC universal input range, the VDC(MIN) is 90V, therefore the LED string voltage VOUT(MAX) should be less than 45V. is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8458A For this particular example : 30  0.2 CIN  = 13.7μF 2 ( 2  90)  902   0.9  60   In addition, the voltage rating of the input filter capacitor, VCIN, should be large enough to handle the input voltage. current and the diode reverse voltage rating should be greater than 1.2 times the maximum input voltage, assuming a ± 20% output current ripple. The peak voltage stress of diode is : VD = 1.2  ( 2  VAC(MAX) ) = 1.2  ( 2  110) = 187V VCIN  (1.2  2  VAC(MAX) ) = (1.2  2  110) = 187V The current rating of diode is : ID = 1.2  IOUT,PK = 1.2  1.2  0.2 = 0.288A Thus, a 22μF / 250V electrolytic capacitor can be chosen in this case. Due to its large ESR, the electrolytic capacitor is not suggested for high current ripple applications. If the input source is universal (VIN = 90V to 264V), VD will reach 448V. A 600V, 2A ultra-fast diode can be used in this example. Inductor Selection MOSFET 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, as shown in equation below :  V   V IL   OUT   1 OUT  VIN   fxL   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. To optimize the ripple current, the RT8458A operates the Buck converter in BCM (Boundary-Condition Mode). The largest ripple current will occur at the highest VIN. To guarantee that the ripple current stays below the specified value, the inductor value should be chosen according to the following equation : V  T  (1 D) L = OUT S 2  IOUT VQ = 1.2  ( 2  VAC(MAX) ) = 1.2  ( 2  110) = 187V = 30  20.83μs  (1 0.333) = 1.04mH 2  0.2 where D is the duty cycle and TS is the switching period. 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. In reality, the peak current through the diode is more than the maximum output current. This component current rating should be greater than 1.2 times the maximum load Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 The peak voltage rating of the MOSFET is : The current rating of MOSFET is : IQ = 1.2  IOUT,PK = 1.2  1.2  0.2 = 0.288A If the input source is universal (VIN = 90V to 264V), VQ will reach 448V. A 600V, 2A N-MOSFET can be chosen for this example. Output Capacitor Selection The selection of COUT is determined by the required ESR to minimize output 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. The output voltage ripple, ΔVOUT, is determined by :   1 VOUT  IL ESR   8fOSCCOUT   where fOSC is the switching frequency and ΔIL is the inductor ripple current. The output voltage ripple will be the 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, is a registered trademark of Richtek Technology Corporation. DS8458A-09 August 2014 RT8458A Thermal Protection A thermal protection feature is included to protect the RT8458A from excessive heat damage. When the junction temperature exceeds a threshold of 150°C, the thermal protection will turn off the GATE terminal. Soldering Process of Pb-free Package Plating To meet the current RoHS requirements, pure tin is selected to provide forward and backward compatibility with both the current industry standard SnPb-based soldering processes and higher temperature Pb-free processes. In the whole Pb-free soldering processes pure tin is required with a maximum 260°C (