RT8458GJ6

® RT8458D High Voltage, High Efficiency, Constant Current PWM Buck Controller for LED Lighting General Description Features The RT8458D is a PWM controller with an internal high side gate driver. Because of the Buck topology, the input voltage for the Buck system is only limited by the voltage rating of the external MOSFET. 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 RT8458D can be up to 100% for wider input voltage application.  The RT8458D also features a 160kHz 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 RT8458D 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 RT8458D is built with the thermal protection function.            Low Cost and Efficient Buck Converter Solution Input Voltage Depends On External MOSFET Programmable Constant LED Current Dimmable LED Current by ACTL 100% Maximum Duty Cycle 160kHz Fixed Switching Frequency 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 Applications  E27, PAR30, Offline LED Lights Marking Information 13= : Product Code 13=DNN DNN : Date Code The RT8458D 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 RVCC D2 RT8458D CVCC CVC2 RVC VCC ACTL VC GATE Analog Dimming Q1 GND SENSE CVC1 RS D1 L1 LED+ COUT LED- Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8458D-07 May 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8458D Ordering Information Pin Configurations (TOP VIEW) RT8458D Package Type J6 : TSOT-23-6 SENSE VC ACTL 6 Lead Plating System G : Green (Halogen Free and Pb Free) 5 4 2 3 Note : VCC GND GATE Richtek products are :  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. Dimming signal can still be applied to ACTL pin. ACTL dimming signal high is internally clamped around 1.3V. The sourcing and sinking current should be limited to no more than 10A. 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. DS8458D-07 May 2014 RT8458D Function Block Diagram + + - VREF Chip Enable 10V/8V OVP + - VCC 35V 160kHz OSC 10V S GATE R 200k R CCOMP GND + - Control Circuit VC SENSE - OTP OP1 + -220mV Dimming ACTL Operation The RT8458D is a PWM Buck current mode controller with an integrated high side gate driver. The start-up voltage of RT8458D is around 10V. Once VCC is above the startup voltage, the RT8458D will maintain operation until VCC drops below 8V. The RT8458D's main control loop consists of a 160kHz 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 RT8458D can turn on up to 100% duty. 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. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8458D-07 May 2014 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 RT8458D 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 RT8458D is built with internal thermal protection function. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8458D 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 16V −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 ---------------------------------------------------------------------------------------------- 10V to 31V Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Electrical Characteristics (VCC = 24V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions VCC_ST Input Start-Up Voltage Minimum Operation Voltage VCC(MIN) After Start-Up Min Typ Max Unit -- 10 12 V -- 8 9 V Maximum Startup Current in IST(MAX) VCC Hiccup Operation Maximum ICC to cause VCC stop hiccup at low end of VCC hysteresis level -- 250 300 A Input Supply Current ICC After Start-Up, VCC = 24V -- 2 5 mA Input Shutdown Current IQC Before Start-Up, VCC = 5V -- 1 5 A 120 160 200 kHz -- -- 100 % -- 88 -- % 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. DS8458D-07 May 2014 RT8458D Parameter Symbol Test Conditions Min Typ Max Unit Current Sense Amplifier Current Sense Voltage V SENSE (Note 5) 213 220 227 mV Sense Input Current I SENSE (Note 7) -- 11 -- A VC Sourcing Current I VC_Source VSENSE = 150mV (Note 7) -- 20 -- A VC Sinking Current I VC_Sink VSENSE = 250mV (Note 7) -- 180 -- A VC Threshold for PWM Switch Off V VC 1.15 1.25 1.35 V No Load at GATE Pin -- 10 16 V IGATE = 50mA -- 9 -- IGATE = 100A -- 9.8 -- IGATE = 50m A -- 0.75 -- 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 -- 0.2 0.5 A GATE Driver Sink Peak Current 1nF Load at GATE -- 0.5 0.8 A VACTL = 1.2V -- 1 5 A LED Current On Threshold at ACTL V ACTL_On -- 1.2 1.3 V LED Current Off Threshold at ACTL V ACTL_Off -- 0.1 0.2 V 32 35 38 V -- 150 -- C GATE Driver Output GATE Pin Maxim um Voltage V GATE GATE Voltage High V GATE_H GATE Voltage Low V GATE_L LED Dimming Analog Dimming ACTL Pin Input Current I ACTL V V OVP Over Voltage Protection V OVP VCC Pin Thermal Protection Thermal Shutdown Temperature T SD 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 RT8458D 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. DS8458D-07 May 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8458D Typical Application Circuit VIN RVCC 180k RB 10 RT8458D 1 VCC CVCC 4.7µF 5 VC CVC2 3.3nF RVC 10k CVC1 1nF 2 GND RACTL 1M ACTL 4 GATE 3 SENSE 6 VIN : 50V VOUT : 30V IOUT : 350mA Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 CIN 10µF/100V D2 1N4148 ZD1 Short Optional RG 0R Q1 Optional RS 0.63 D1 SK36C L1 200µH LED+ COUT 220µF/50V LED- is a registered trademark of Richtek Technology Corporation. DS8458D-07 May 2014 RT8458D Typical Operating Characteristics Efficiency vs. Input Voltage Output Current vs. Input Voltage 100 354 353 Output Current (mA) Efficiency (%) 96 92 13LED 11LED 9LED 7LED 5LED 3LED 88 84 352 351 350 3LED 5LED 7LED 9LED 11LED 13LED 349 348 347 VIN = 18V to 50V, IOUT = 350mA, LED 3 to 13 pcs VIN_AC = 18V to 50V, IOUT = 350mA, LED 3 to 13 pcs 80 346 18 22 26 30 34 38 42 46 50 18 22 26 30 Input Voltage (V) 38 42 46 50 Input Voltage (V) Switching Frequency vs. Supply Voltage Switching Frequency vs. Temperature 174 Switching Frequency (kHz)1 171 Switching Frequency (kHz)1 34 170 169 168 167 166 165 172 170 168 166 164 162 160 158 156 164 154 0 4 8 12 16 20 24 28 32 -50 36 -25 0 25 50 75 100 125 Temperature (°C) Supply Voltage (V) SENSE Threshold vs. Supply Voltage SENSE Threshold vs. Temperature 221.0 224 SENSE Threshold (mV) SENSE Threshold (mV) 222 220.5 220.0 219.5 219.0 218.5 220 218 216 214 212 210 208 218.0 206 0 4 8 12 16 20 24 28 32 Supply Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8458D-07 May 2014 36 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8458D Output Current vs. Output Voltage 370 350 366 Output Current (mA) SENSE Threshold (mV) SENSE Threshold vs. ACTL Voltage 400 300 250 200 150 100 362 358 354 350 346 342 338 50 334 VIN = 24V, IOUT = 350mA, LED 5 pcs, L = 1mH 0 VIN = 50V, IOUT = 350mA, LED 3 to 13 pcs, L = 0.2mH 330 0 0.5 1 1.5 2 2.5 3 8 18 23 28 33 ACTL Voltage (V) Output Voltage (V) Power On Power Off VIN (20V/Div) VIN (20V/Div) VOUT (20V/Div) VOUT (20V/Div) IOUT (200mA/Div) IOUT (200mA/Div) VIN = 50V, IOUT = 350mA, LED 10 pcs, L = 1mH Time (25ms/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 13 38 43 VIN = 50V, IOUT = 350mA, LED 10 pcs, L = 1mH Time (25ms/Div) is a registered trademark of Richtek Technology Corporation. DS8458D-07 May 2014 RT8458D Application Information The RT8458D is a high efficiency PWM Buck LED controller for high brightness LED application. Its high side gate driver is used to control the Buck converter via an external MOSFET and regulate the constant output current. 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. If VACTL becomes larger than 1.2V, the output current value will just be determined by the external resistor, RS. The RT8458D can achieve high accurate 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 160kHz 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. IOUTavg = (0.22V / RS )  Start-Up Resistor Start-up resistor should be chosen not to exceed the maximum start-up current. Otherwise, the RT8458D may latch low and will never start. The maximum start-up current is VIN / RVCC. Under Voltage Lockout (UVLO) The RT8458D includes a UVLO feature with 2V hysteresis. The GATE terminal turns on when VIN rises over 10V (typ.). The GATE terminal turns off when VIN falls below 8V (typ.) VCC Supplied from Auxiliary Winding Auxiliary winding can be added to the main step-down converter with coupled inductor. Because the diode voltage drop and the RT8458D controller regulate the output current, the inductor's voltage drop is also relatively constant during the OFF time. To remain output average current, the main inductor should be in continuous current conduction throughout the step-down load range. 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 terminal. The relationship between output current, IOUT, and RS is shown below : IOUT = 0.22 RS VACTL  0.1 1.1 (A) VIN RVCC CIN D2 RT8458D CVCC VCC RACTL ACTL VC CVC GATE GND SENSE Q1 AUX RS D1 L1 COUT LED+ ROUT LED- Figure 1. VCC Supplied from Auxiliary Winding Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8458D-07 May 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8458D Three functions are needed to set the value of the main inductor : the voltage across the inductor, the operating frequency, and the inductor's current ripple. These functions will ensure that adequate energy is stored in the inductor together. The Auxiliary output voltage VAUX to VCC is given by : Inductor Selection VAUX = N2 / N1 (VOUT + VD1) − VD2 N2 = primary turns and N2 = secondary turns.  V   V IL   OUT   1 OUT  VIN   fxL   The VAUX design value should be set below 31V for RT8458D OVP limitation in normal operation. This output in Figure 1 is independent of input voltage changes, as D2 is ON when the MOSFET OFF. For a given inductor value, secondary power at the auxiliary output is limited by the onset of discontinuous current in the main primary loop. To optimize the ripple current, the RT8458D 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 : To use Auxiliary output to supply the VCC, the Minimum load is required to place a resistor as load at the output. L= If VIN > output LED forward voltage, the leakage current (~2mA) which is RT8458D operating Current will pass through the output LED. This leakage current will light on the output LED. To avoid this leakage current pass through LED, place a resistor between LED+ and LED−. The resistor value is (VOUT / 2mA) and the consume power is about (VOUT x 2mA). 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. For most of the RT8458D applications, a 10μF ceramic capacitor is sufficient. Use of X7R type ceramic capacitors is recommended. Lower operating frequencies will require proportionately higher capacitor values. Thus, a 10μF / 100V electrolytic capacitor can be chosen in this case due to its low ESR. Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 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 : VOUT  TS  (1 D) 2  IOUT where D is the duty cycle and TS is the switching period. Forward Diode Selection The Schottky diode, with their low forward voltage drop and fast switching speed, is necessary for the RT8458D applications. In addition, power dissipation, reverse voltage rating and pulsating peak current are also important parameters for the Schottky diode selection. Choose a suitable Schottky diode with reverse voltage rating greater than the maximum output voltage. The diode's average current rating must exceed the average output current. The diode conducts current only when the power switch is turned off (typically less than 50% duty cycle). If using the PWM feature for dimming, it is important to consider diode leakage, which increases with temperature, from the output during the PWM low interval. Therefore, a Schottky diode with sufficiently low leakage current is suggested. MOSFET Selection For applications operating at high input or output voltages, the power N-MOSFET switch is typically chosen for drain voltage, VDS, rating and low gate charge. Consideration of switch on-resistance, R DS(ON), is usually secondary because switching losses dominate power loss. is a registered trademark of Richtek Technology Corporation. DS8458D-07 May 2014 RT8458D Output Capacitor Selection Thermal Considerations 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 : For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and   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, aluminum electrolytic and ceramic capacitors are all common selections and available in surface mount packages. Tantalum capacitors have the highest capacitance density, but it is important to only use ones that pass the surge test for use in switching power supplies. Special polymer capacitors offer very low ESR value, but with the trade-off of lower capacitance density. Aluminum electrolytic capacitors have significantly higher ESR, but still can be used in cost-sensitive applications for ripple current rating and long term reliability considerations. difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(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 recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For TSOT-23-6 package, the thermal resistance, θJA, is 255°C/ W on a standard JEDEC 51-3 single-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : PD(MAX) = (125°C − 25°C) / (255°C/W) = 0.392W for TSOT-23-6 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. A thermal protection feature is included to protect the RT8458D 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 (