TPS92314 TPS92314A www.ti.com SNVS856B – JUNE 2012 – REVISED MAY 2013 Off-Line Primary Side Sensing Controller with PFC Check for Samples: TPS92314, TPS92314A FEATURES DESCRIPTION • The TPS92314/14A is an off-line controller specifically designed to drive high power LEDs for lighting applications. Features include adaptive constant on-time control and quasi-resonant switching. Resonant switching allows for a reduced EMI signature and increased system efficiency. Thus, the device introduces a low external parts count and high level of integration. The control algorithm of TPS92314/14A adjusts the on time with reference to the primary side inductor peak current and secondary side inductor discharge time dynamically, the response time of which is set by an external capacitor. 1 2 • • • • • • • • Regulates LED Current Without Secondary Side Sensing Adaptive ON-time Control with Inherent PFC Critical-Conduction-Mode (CRM) with ZeroCurrent Detection (ZCD) for Valley Switching Programmable Switch Turn ON Delay Programmable Constant ON-Time (COT) Over Current Limit Options: – TPS92314: 1.15V – TPS92314A: 2.0V Advanced Over Current and Over Voltage Protection Internal Over-temperature Protection 8-Pin SOIC Package The over current protection is implemented by a cycle by cycle current limit of the primary inductor current. TPS92314A has a higher OCP threshold which is more suitable for universal line application and TPS92314 can optimize the system cost. Other supervisory features of the TPS92314/14A include VCC over voltage protection and under-voltage lockout, output LEDs over-voltage protection and controller thermal shutdown. The TPS92314/14A is available in 8-pin SOIC package. APPLICATIONS • • Residential LED Lamps: A19 (E26/27, E14), PAR30/38, GU10 Solid State Lighting spacer TYPICAL APPLICATION DOUT LED+ ZSN T1 R1a CIN D1 AC IN DSN LP LS 6±7 LED R1b DVCC COUTa RVCC RAUX1 CVCC DZCD COUTb LAUX LED- RAUX2 CY1 Q1 TPS92314 VCC GATE AGND ISNS ZCD PGND COMP DLY CCOMP RFILTER RISNS RDLY 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2012–2013, Texas Instruments Incorporated TPS92314 TPS92314A SNVS856B – JUNE 2012 – REVISED MAY 2013 www.ti.com VCC 1 8 GATE AGND 2 7 ISNS ZCD 3 6 PGND COMP 4 5 DLY Figure 1. 8-Pin SOIC (Top View) See D Package PIN DESCRIPTIONS 2 Pin Name Description 1 VCC Power supply Input This pin provides power to the internal control , connect a 10μF~20μF capacitor to ground for filtering. 2 AGND Small signal Ground Control signal ground return. 3 ZCD Zero crossing detection input 4 COMP Compensation network 5 DLY Delay control input 6 PGND Power Ground 7 ISNS 8 GATE Application Information The pin senses the voltage of the auxiliary winding for zero current detection. Output of the error amplifier. Connect a capacitor from this pin to ground to determine the frequency response of average current control loop. Connect a resistor from this pin to ground to set the delay between switching ON and OFF periods. Gate driver ground return. Current sense voltage feedback Switching MOSFET current sense pin. Gate driver output Submit Documentation Feedback The output provides the gate driver of the power switching MOSFET. Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A TPS92314 TPS92314A www.ti.com SNVS856B – JUNE 2012 – REVISED MAY 2013 These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. ABSOLUTE MAXIMUM RATINGS (1) VALUE / UNITS VCC to GND –0.3V to 40V DLY,COMP,ZCD to GND –0.3V to 7V ISNS to GND –0.3V to 7V GATE to GND (5ns,-6V) -0.3V to 12V ESD Susceptibility: HBM (2) ±2 kV Storage Temperature Range –65°C to +150°C Junction Temperature (TJ-MAX) +150°C Maximum Lead Temperature (Solder and Reflow) 260°C (1) (2) Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is intended to be functional, but device parameter specifications may not be ensured. For specifications and test conditions, see the Electrical Characteristics. All voltages are with respect to the potential at the GND pin, unless otherwise specified. Human Body Model, applicable std. JESD22-A114-C. RECOMMENDED OPERATING CONDITIONS VALUE / UNITS Supply Voltage range VCC 13V to 35V Junction Temperature (TJ) -40°C to +125°C Thermal Resistance (θJA) (1) (1) 162°C/W This RθJA typical value determined using JEDEC specifications JESD51-1 to JESD51-11. However junction-to-ambient thermal resistance is highly board layout dependent. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues during board design. In high-power dissipation applications, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 125°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (RθJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX). ELECTRICAL CHARACTERISTICS VCC = 18V unless otherwise indicated. Typicals and limits appearing in plain type apply for TA = TJ = +25°C. Limits appearing in boldface type apply over the full Operating Temperature Range. Data sheet minimum and maximum specification limits are specified by design, test or statistical analysis. Symbol Parameter Conditions Min Typ (1) Max Units SUPPLY VOLTAGE INPUT (VCC) VCC-UVLO VCC Turn on threshold 22.5 / 21.7 25.4 28.3 / 29.5 V VCCTurn off threshold 10.4 / 10.1 12.9 15.3 / 16.0 V µA Hysteresis ISTARTUP Startup Current VCC-OVP Over voltage protection threshold IVCC Operating supply current 12.5 VCC=VCC-UVLO–3.0V Not switching 22.2 25.8 32.7 35.5 38.0 V 0.8 1.2 1.8 mA 2.3 3.0 mA 0.01 1 uA 4.3 4.7 65kHz switching ZERO CROSS DETECT (ZCD) IZCD ZCD bais current VZCD-OVP ZCD over-voltage threshold VZCD= 5V TOVP Over voltage de-bounce time VZCD-ARM ZCD Arming threshold VZCD = Increasing 1.04 1.23 1.42 V VZCD-TRIG ZCD Trigger threshold VZCD = Decreasing 0.48 0.6 0.77 V VZCD-HYS ZCD Hysteresis VZCD-ARM-VZCD-TRIG 3.9 3 V cycle 0.61 V 27 µA COMPENSATION (COMP) ICOMP-SOURCE (1) Internal reference current for primary side current regulation VCOMP = 2.0V, VISNS = 0V, Measure at COMP pin Typical numbers are at 25°C and represent the most likely norm. Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A Submit Documentation Feedback 3 TPS92314 TPS92314A SNVS856B – JUNE 2012 – REVISED MAY 2013 www.ti.com ELECTRICAL CHARACTERISTICS (continued) VCC = 18V unless otherwise indicated. Typicals and limits appearing in plain type apply for TA = TJ = +25°C. Limits appearing in boldface type apply over the full Operating Temperature Range. Data sheet minimum and maximum specification limits are specified by design, test or statistical analysis. Symbol Parameter Conditions gmISNS ISNS error amp trans-conductance Δ VISNS to Δ ICOMP at VCOMP = 2.5V Min Typ (1) Max 96 Units µmho DELAY CONTROL (DLY) VDLY DLY pin internal reference voltage IDLY-MAX DLY source current 1.21 1.24 VDLY= 0V 250 450 1.3 V µA CURRENT SENSE (ISNS) VISNS-OCP Over Current Limit Detection Threshold TPS92314 1.07 1.15 1.22 VISNS-OCP Over Current Limit Detection Threshold TPS92314A 1.90 2.0 2.10 V IISNS Current Sense Bias Current VISNS= 5V 1 µA TOCP Over current Limit Detection Propagation Delay Measure ISNS pin pulse width with VISNS = 5V -1 256 V ns GATE DRIVER (GATE) VGATE-H GATE low voltage IGATE = 50mA source VGATE-L GATE high drive voltage IGATE = 50mA sink 7.6 9.4 85 tGATE-RISE Rise Time CLOAD = 1nF 94 tGATE-FALL Fall Time CLOAD = 1nF 16 TON-MIN Minimum ON time With ZCD signal. TON-MAX V 125 mV ns ns 311 500 900 ns Maximum ON time 27 43.9 61 µs TOFF-MIN Minimum OFF time 1.00 1.50 1.93 µs TOFF-MAX Maximum OFF time ZCD = GND 67 117 151 µs TOFF-START Maximum OFF time when start up. Maximum OFF time at first 511 switching after UVLO 44 78 102 µs TOFF-OCP Maximum OFF time when OCP OFF time when VISNS =4V. 233 µs 165 °C 20 °C THERMAL SHUTDOWN TSD Thermal shutdown temperature See (2) Thermal Shutdown hysteresis (2) 4 Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 165°C (typ.) and disengages at TJ = 145°C (typ). Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A TPS92314 TPS92314A www.ti.com SNVS856B – JUNE 2012 – REVISED MAY 2013 TYPICAL PERFORMANCE CHARACTERISTICS All curves taken at VCC=18V with configuration in typical application for driving seven power LEDs with ILED=350mA shown in this datasheet. TA=25°C, unless otherwise specified. 15.0 VCC-UVLO vs Temperature 28 VCCSTARTUP VOLTAGE (V) 14.5 14.0 VCC-UVLO(V) VCC Startup Voltage vs Temperature 29 13.5 13.0 12.5 12.0 11.5 27 26 25 24 23 22 11.0 -50 150 21 -25 0 25 50 75 TEMPERATURE (°C) Figure 2. 100 125 -50 TOFF-MAX vs Temperature 580 TON-MIN(ns) TOFF-MAX( s) 120 110 100 520 500 480 440 80 420 -25 0 25 50 75 TEMPERATURE (°C) Figure 4. 100 125 -50 -25 IVCC-SD vs Temperature 4.7 0 25 50 75 100 125 TEMPERATURE (°C) Figure 5. VZCD-OVP vs Temperature 4.6 2.8 4.5 VZCD-OVP(V) 2.6 IVCC-SD(mA) TON-MIN vs Temperature 460 90 2.4 2.2 4.4 4.3 4.2 2.0 4.1 1.8 4.0 1.6 -50 100 125 540 130 3.0 0 25 50 75 TEMPERATURE (°C) Figure 3. 560 140 -50 -25 3.9 -25 0 25 50 75 TEMPERATURE (°C) Figure . 100 125 -50 Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A -25 0 25 50 75 TEMPERATURE (°C) Figure 6. 100 125 Submit Documentation Feedback 5 TPS92314 TPS92314A SNVS856B – JUNE 2012 – REVISED MAY 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS (continued) All curves taken at VCC=18V with configuration in typical application for driving seven power LEDs with ILED=350mA shown in this datasheet. TA=25°C, unless otherwise specified. 1.50 VZCD-ARM vs Temperature 1.45 0.75 0.70 1.35 VZCD-TRIG(V) VZCD-ARM(V) 1.40 1.30 1.25 1.20 1.15 0 25 50 75 TEMPERATURE (°C) Figure 7. VISNS_OCP vs Temperature 1.18 2.15 1.17 2.10 1.16 1.15 1.14 100 125 2.05 2.00 1.95 TPS92314A 1.85 1.80 -25 0 25 50 75 TEMPERATURE (°C) Figure 9. 100 125 -50 VDLY vs Temperature 1.28 1.26 36.5 VCCOVP(V) 37.0 1.25 1.24 1.23 0 25 50 75 TEMPERATURE °C Figure 10. 100 125 36.0 35.5 35.0 1.22 34.5 1.21 34.0 1.20 -25 VCC-OVP vs Temperature 37.5 1.27 -50 0 25 50 75 TEMPERATURE (°C) Figure 8. 1.90 1.12 1.11 -50 -25 VISNS_OCP vs Temperature 2.20 TPS92314 VDLY(V) 0.56 0.40 -50 100 125 VISNS-OCP(V) VISNS-OCP(V) -25 1.13 6 0.60 0.45 1.05 1.19 0.65 0.50 1.10 1.00 -50 VZCD-TRIG vs Temperature 0.80 33.5 -25 0 25 50 75 TEMPERATURE (°C) Figure 11. Submit Documentation Feedback 100 125 -50 -25 0 25 50 75 TEMPERATURE (°C) Figure 12. 100 125 Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A TPS92314 TPS92314A www.ti.com SNVS856B – JUNE 2012 – REVISED MAY 2013 SIMPLIFIED INTERNAL BLOCK DIAGRAM VCC BIAS & VREF UVLO VOCP_TH VREF VC1 DRV GATE VCC_UVLO_TH AGND VCC_OV PGND VCC_OV_TH TSD VTRIG/VARM ZC ZCD TON Peak Hold VONpk CONTROL LOGIC LEB LEB OCP ISNS ZCD_OVP TON ON VOCP_TH ROCP VC1 Internal Ramp IREF D UVLO DRV COMP OFT ZC DELAY ON IDLY VONpk V/I DLY Figure 13. Simplified Block Diagram Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A Submit Documentation Feedback 7 TPS92314 TPS92314A SNVS856B – JUNE 2012 – REVISED MAY 2013 www.ti.com APPLICATION INFORMATION The TPS92314/14A is an off-line controller specifically designed to drive LEDs. This device operates in Critical Conduction Mode (CRM) with adaptive Constant ON-Time control, so that high power factor can be achieved naturally. The TPS92314/14A can be configured as an isolated or non-isolated off-line converter. Refer to TPS92314/14A typical schematic, on the front page, in the following discussion. The TPS92314/14A flyback converter consists of a transformer which includes three windings LP, LS and LAUX. An external MOSFET Q1 and inductor current sensing resistor RISNS. Secondary side components are secondary side transformer winding LS, output diode DOUT, and output capacitor COUT. An auxiliary winding is required, and serves two functions. Auxiliary power is developed from the winding to power the TPS92314/14A after start-up, and detect the zero crossing point due to the end of a complete switching cycle. During the on-period, Q1 is turned on, and current flows through LP, Q1 and RISNS to ground, input energy is stored in the primary inductor LP. Simultaneously, the ISNS pin of the device monitors the voltage of the current sensing resistor RISNS to perform the cycle-by-cycle inductor current limit function. During the time MOSFET Q1 is off, current flow in LP ceases and the energy stored during the on cycle is released to output and auxiliary circuits. During Q1 off-time current in the secondary winding LS charges the output capacitor COUT through DOUT and supplies the LED load. During Q1 on-time, COUT is responsible to supply load current to LED load during subsequent on-period. Also during Q1 off-time current is delivered to the auxiliary winding through DVCC and powers the TPS92314/14A. The voltage across LAUX, VLAUX is fed back to the ZCD pin through a resistor divider network formed by RAUX1 and RAUX2 to perform zero crossing detection of VLAUX, which determines the end of the off-period of a switching cycle. The next on period of a new cycle will be initiated after an inserted delay of 2 x tDLY. The tDLY is programmable by a single resistor connecting the DLY pin and ground. The setting of the delay time, tDLY will be described in a separate paragraph. The driver signal tON time width is generated by comparing an internal generated saw-tooth waveform with the voltage on the COMP pin (VCOMP). Since VCOMP is slow varying, tON is nearly constant within an AC line cycle. The duration of the off-period (tOFF) is determined by the rate of discharging of the secondary current through the transformer. Also, where • n is the turn ratio of LP and LS. (1) Figure 14 shows the typical waveforms in normal operation. 8 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A TPS92314 TPS92314A www.ti.com SNVS856B – JUNE 2012 – REVISED MAY 2013 VSW t 2xtDLY ILP VCOMP t tON ILS ILED t tOFF VZCD VZCD-OVP VZCD-PEAK VZCD-ARM VZCD-TRIG t tDLY Figure 14. Primary and Secondary Side Current Waveforms Startup Bias and UVLO During startup, the TPS92314/14A is powered from the AC line through R1 and bridge diode D1 (Typical Application on front page). In the startup state, most of the internal circuits of the TPS92314/14A are shut down in order to minimize internal quiescent current. When VCC reaches the rising threshold of the VCC-UVLO (typically 26V), the TPS92314/14A is operating in a low switching frequency mode, where tON and tOFF are fixed to 1.5μs and 72μs. When VZCD–PEAK is higher than VZCD-ARM, the TPS92314/14A enters normal operation. Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A Submit Documentation Feedback 9 TPS92314 TPS92314A SNVS856B – JUNE 2012 – REVISED MAY 2013 www.ti.com VSW Low Freq state Steady state Startup state t VCC 26V t VZCD VZCD-OVP VZCD-ARM t Figure 15. Start up Bias Waveforms Zero Crossing Detection To minimized the switching loss of the power MOSFET, a zero crossing detection circuit is embedded in the TPS92314/14A. VLAUX is AC voltage coupled from VSW by means of the transformer, with the lower part of the waveform clipped by DZCD. VLAUX is fed back to the ZCD pin to detect a zero crossing point through a resistor divider network which consists of RAUX1 and RAUX2. The next turn on time of Q1 is selected VSW is the minimum, an instant corresponding to a small delay after the zero crossing occurs. (Figure 15) The actual delay time depends on the drain capacitance of the Q1 and the primary inductance of the transformer (LP). Such delay time is set by a single external resistor as described in Delay Setting section. During the off-period at steady state, VZCD reaches its maximum VZCD-PEAK (Figure 14), which is scalable by the turn ratio of the transformer and the resistor divider network RAUX1 and RAUX2. It is recommended that VZCD-PEAK is set to 3V during normal operation. n u VLED +VIN n u VLED VSW tDLY Figure 16. Switching Node Waveforms 10 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A TPS92314 TPS92314A www.ti.com SNVS856B – JUNE 2012 – REVISED MAY 2013 Delay Time Setting In order to reduce EMI and switching loss, the TPS92314/14A inserts a delay between the off-period and the onperiod. The delay time is set by a single resistor which connects across the DLY pin and ground, and their relationship is shown in Figure 17. The optimal delay time depends on the resonance frequency between LP and the drain to source capacitance of Q1 (CDS). Circuit designers should optimize the delay time according to the following equation. (2) (3) After determining the delay time, tDLY can be implemented by setting RDLY according to the following equation: where • KDLY = 32MΩ/ns is a constant (4) 60 RDLY(k ) 50 40 30 20 10 0 0 400 800 1200 1600 DELAY TIME (ns) 2000 Figure 17. Delay Time Setting Protection Features OUTPUT OPEN CIRCUIT PROTECTION The open circuit protection can be trigger through ZCD pin or VCC pin. If the LED string is disconnected from the output of the TPS92314/14A, The secondly output voltage (VLED) and AUX wiring voltage VZCD-PEAK will increases. IF VZCD-PEAK is greater than VZCD-OVP for 3 continues switching cycles or VCC voltage higher than VCCOVP threshold, Over Voltage Protection (OVP) protection will be trigger. At the meantime, switching of Q1 will stop and VCC will decreases until it drops below the falling threshold of VCC-UVLO, the controller will restarts automatically and enter into startup state (Figure 19). VCC OVP PROTECTION The TPS92314/14A has a built-in over voltage protection feature. It can be trigger through the VCC pin when over VCC-OVP threshold. Once the VCC-OVP triggered, the output gate signal will pull low and VCC will decrease until it drops below the VCC-UVLO, the controller will restarts automatically. Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A Submit Documentation Feedback 11 TPS92314 TPS92314A SNVS856B – JUNE 2012 – REVISED MAY 2013 www.ti.com OUTPUT SHORT CIRCUIT PROTECTION If the LED string is shorted, the voltage of AUX wiring (VZCD-PEAK) will decrease, and as VZCD-PEAK voltage decrease below VZCD-TRIG, the TPS92314/14A will enter low switching frequency operation. During low switching frequency operation, power supplied from LAUX to VCC is not enough to maintain VCC. If the short remains VCC will drop below the falling threshold of VCC-UVLO, the TPS92314/14A will attempt to restart at this time (Figure 18). When the short is removed the TPS92314/14A will restore to steady state operation. VSW Steady state Low freq state Low freq state t VCC 26V 13V t VZCD VZCD-OVP VZCD-ARM t VLED t Figure 18. Output Short Circuit waveforms OVER CURRENT PROTECTION Over Current Protection (OCP) limits the drain current of MOSFET and prevents inductor / transformer saturation. When VISNS reaches a threshold, OCP function will be triggered, controller gate drive will pull low and OFF time will extends to 233μs, also CCOMP capacitor will be discharged by internal switch and gate drive ON time will force to minimum in next cycle. THERMAL PROTECTION Thermal protection is implemented by an internal thermal shutdown circuit, which activates at 165°C (typically). In this case, the switching power MOSFET will turn off. Capacitor CVCC will discharge until UVLO. If the junction temperature of the TPS92314/14A falls back below 145°C, the TPS92314/14A resumes normal operation. 12 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A TPS92314 TPS92314A www.ti.com SNVS856B – JUNE 2012 – REVISED MAY 2013 Steady state Startup state Low Freq state VSW OV state Steady state Disconnect LED Reconnect LED Steady state Startup state Startup state Startup state Low Freq state VCC VCC_OVP 26V 13.2V VZCD VZCD-OVP VZCD-ARM VLED ILED Steady state Force output short circuit Steady state Figure 19. Auto Restart Operation Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A Submit Documentation Feedback 13 TPS92314 TPS92314A SNVS856B – JUNE 2012 – REVISED MAY 2013 www.ti.com Design Example The following design example illustrates the procedures to calculate the external component values for the TPS92314/14A isolated single stage fly-back LED driver with PFC. • Design Specifications: – Input voltage range, VAC_RMS = 85VAC – 132VAC – Nominal input voltage, VAC_RMS(NOM) = 110VAC – Number of LED in serial =7 – LED current, ILED = 350mA – Forward voltage drop of single LED = 3.0V – Forward voltage of LED stack, VLED = 21V • Key operating Parameters: – Converter minimum switching frequency, fSW = 75kHz – Output rectifier maximum reverse voltage, VDOUT(MAX) = 100V – Power MOSFET rating, VQ1(MAX) =800V – Power MOSFET Output Capacitance, CDS = 37pF (estimated) – Nominal output power, POUT = 8W START UP BIAS RESISTOR During start up, the VCC will be powered by the rectified line voltage through external resistor, R1. The VCC start up current, IVCC(SU) must set in the range IVCC(MIN) > IVCC(SU) > ISTARTUP(MAX) to ensure proper restart operation during OVP fault at maximum voltage input. In this example, a value of 0.88mA is suggested. The resistance of R1 can be calculated by dividing the nominal input voltage in RMS by the start up current suggested. So, RAC = 132V / 0.88mA = 150KΩ is recommended. TRANSFORMER TURN RATIO The transformer winding turn ratio, n is governed by the MOSFET Q1 maximum rated voltage, (VQ1(MAX)), highest line input peak voltage (VAC-PEAK) and output diode maximum reverse voltage rating (VOUT(MAX)). The output diode rating limits the lower bound of the turn ratio and the power MOSFET rating provide the upper bound of the turn ratio. The transformer turn ratio must be selected in between the bounds. If the maximum reverse voltage of DOUT (VDOUT(MAX)) is 100V. the minimum transformer turn ratio can be calculated with the equation in below. (5) In operation, the voltage at the switching node, VSW must be small than the MOSFET maximum rated voltage VQ1(MAX) , For reason of safety, 10% safety margin is recommended. Hence, 90% of VQ1(MAX) is used in the following equation. (6) where • VOS is the maximum switching node overshoot voltage allowed, in this example, 50V is assumed. (7) As a rule of thumb, lower turn ratio of transformer can provide a better line regulation and lower secondly side peak current. In here, turn ratio n = 3.8 is recommended. 14 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A TPS92314 TPS92314A www.ti.com SNVS856B – JUNE 2012 – REVISED MAY 2013 SWITCHING FREQUENCY SELECTION TPS92314/14A can operate at high switching frequency in the range of 60kHz to 150kHz. In most off-line applications, with considering of efficiency degradation and EMC requirements, the recommended switching frequency range will be 60kHz to 80kHz. In this design example, switching frequency at 75kHz is selected. SWITCHING ON TIME The maximum power switch on-time, tON depends on the low line condition of 85VAC. At 85VAC the switching frequency was chosen at 75kHz. This transformer design will follow the formulae as shown below. (8) TRANSFORMER PRIMARY INDUCTANCE The primary inductance, LP of the transformer is related to the minimum operating switching frequency fSW, converter output power POUT, system efficiency η and minimum input line voltage VAC_RMS(MIN). For CRM operation, the output power, POUT can be described by the equation in below. (9) By re-arranging terms, the transformer primary inductance required in this design example can be calculated with the equation follows: (10) The converter minimum switching frequency is 75kHz, tON is 5.3µs, VAC_RMS(MIN) = 85V and POUT = 8W, assume the system efficiency, η = 85%. Then, (11) From the calculation in above, the inductance of the primary winding required is 0.81mH. After the primary inductance and transformer turn ratio is determined, the current sensing resistor, RISNS can be calculated. The resistance for RISNS is governed by the output current and transformer turn ratio, the equation in below can be used. where • VREF is fixed to 0.14V internally. (12) Transformer turn ratio, NP : NS is 3.8 : 1 and ILED = 0.35A (13) In Figure 20, resistor RFILTER is used to reduce the high frequency noise into ISNS pin. the typical value is 300 x RISNS . Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A Submit Documentation Feedback 15 TPS92314 TPS92314A SNVS856B – JUNE 2012 – REVISED MAY 2013 www.ti.com Q1 TPS92314 GATE RFILTER ISNS PGND DLY RISNS RDLY Figure 20. RISNS Resistor Interface DVCC VCC RAUX1 LAUX ZCD DZCD PGND RAUX2 PGND PGND Figure 21. Auxiliary Winding Interface to ZCD Auxiliary Winding Interface To ZCD In Figure 21, RAUX1 and RAUX2 forms a resistor divider which sets the thresholds for over voltage protection of VLED, VZCD-OVP, and VZCD-PEAK. Before the calculation, we need to set the voltage of the auxiliary winding, VLAUX at open circuit. • For example : – Assume the nominal forward voltage of LED stack (VLED) is 21V. – To avoid false triggering ZCDOVP voltage threshold at normal operation, select ZCDOVP voltage at 1.3 times of the VLED is typical in most applications. In case the transformer leakage is higher, the ZCDOVP threshold can be set to 1.5 times of the VLED. – In this design example, open circuit AUX winding OVP voltage threshold is set to 30V. Assume the current through the AUX winding is 0.4mA typical. – As a result, RAUX1 is 66kΩ and RAUX2 is 12kΩ. Auxiliary Winding Vcc Diode Selection The VCC diode DVCC provides the supply current to the converter, low temperature coefficient , low reverse leakage and ultra fast diode is recommended. Compensation Capacitor And Delay Timer Resistor Selection To achieve PFC function with a constant on time flyback converter, a low frequency response loop is required. In most applications, a 4.7µF CCOMP capacitor is suitable for compensation. 16 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A TPS92314 TPS92314A www.ti.com SNVS856B – JUNE 2012 – REVISED MAY 2013 TPS92314 VCC GATE AGND ISNS ZCD PGND COMP DLY CCOMP RDLY AGND Figure 22. Compensation and DLY Timer connection The resistor RDLY connecting the DLY pin to ground is used to set the delay time between the ZCD trigger to power MOSFET turn on. The delay time required can be calculated with the parasitic capacitance at the drain of MOSFET to ground and primary inductance of the transformer. Equation 14 can be used to find the delay time and Figure 17 can help to find the resistance once the delay time is calculated (14) For example, using a transformer with primary inductance LP = 1mH, and power MOSFET drain to ground capacitor CDS=37pF, the tDLY can be calculated by the upper equation. As a result, tDLY=302ns and RDLY is 6.31kΩ. The delay time may need to change according to the primary inductance of the transformer. The typical level of output current will shift if inappropriate delay time is chosen. Output Flywheel Diode Selection To increase the overall efficiency of the system, a low forward voltage schottky diode with appropriate rating should be used. Primary Side Snubber Design The leakage inductance can induce a high voltage spike when power MOSFET is turned off. Figure 23 illustrates the operation waveform. A voltage clamp circuit is required to protect the power MOSFET. The voltage of snubber clamp (VSN) must be higher than the sum of over shoot voltage (VOS), LED open load voltage multiplied by the transformer turn ratio (n). In this examples, the VOS is 50V and LED maximum voltage, VLED(MAX) is 30V, transformer turn ratio is 3.8. The snubber voltage required can be calculated with following equations. VOS VSN VMOS_BV n u VLED VAC_PEAK Vsw Figure 23. Snubber Waveform (15) where n is the turn ratio of the transformer. (16) At the same time, sum of the snubber clamp voltage and VAC peak voltage (VAC_PEAK) must be smaller than the MOSFET breakdown voltage (VMOS_BV). By re-arranging terms, equation in below can be used. Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A Submit Documentation Feedback 17 TPS92314 TPS92314A SNVS856B – JUNE 2012 – REVISED MAY 2013 www.ti.com (17) In here, snubber clamp voltage, VSN = 250V is recommended. Output Capacitor The capacitance of the output capacitor is determined by the equivalent series resistance (ESR) of the LED, RLED and the ripple current allowed for the application. The equation in below can be used to calculate the required capacitance. (18) Assume the ESR of the LED stack contains 7 LEDs and is 2.6Ω, AC line frequency fAC is 60Hz. In this example, LED current ILED is 350mA and output ripple current is 30% of ILED: (19) Then, COUT = 480μF. In here, a 470μF output capacitor with 10μF ceramic capacitor in parallel is suggested. PCB Layout Considerations The performance of any switching power supplies depend as much upon the layout of the PCB as the component selection. Good layout practices are important when constructing the PCB. The layout must be as neat and compact as possible, and all external components must be as close as possible to their associated pins. High current return paths and signal return paths must be separated and connect together at single ground point. All high current connections must be as short and direct as possible with thick traces. The drain voltage of the MOSFET should be connected close to the transformer pin with short and thick trace to reduce potential electromagnetic interference. For off-line applications, one more consideration is the safety requirements. The clearance and creepage to high voltage traces must be complied to all applicable safety regulations. 18 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A TPS92314 TPS92314A www.ti.com SNVS856B – JUNE 2012 – REVISED MAY 2013 DOUT 1A 100V L1 3.3 mH LED+ 250V 0.5A 90-132VAC RAC 22Q/1W R1a 75k D1 VR1 CIN2 CIN1 0.1 F 0.1 F CIN3 0.1 F R1b 75k CAC 47 nF T1 1A 600V LP COUTa 10 F RVCC 20Q DVCC RAUX1 66 kQ VCC 10 F DZCD VCC GATE AGND ISNS ZCD PGND COMP DLY COUTb 470 F 6±7 LED RL 49.9 kQ LAUX RAUX2 12 kQ LEDCY1 2200 pF 2A 800V TPS92314 CCOMP 4.7 F LS NP : NS : NAUX = 3.8 : 1 : 1 RF 450Q RISNS 1.5Q RDLY 6.34 kQ Figure 24. Isolated Topology Schematic L1 3.3 mH LED+ 0.5A RAC 22Q/1W R1a 75k D1 90-132VAC VR1 CIN2 0.1 F CIN1 0.1 F R1b 75k CAC 47 nF DVCC CIN3 0.1 F T1 LP COUTa 10 F RVCC 20Q RAUX1 66 kQ VCC 10 F DZCD VCC GATE AGND ISNS ZCD PGND COMP DLY RDLY 6.34 kQ COUTb 470 F RL 49.9 kQ 6±7 LED LAUX RAUX2 12 kQ LED- NP:NAUX = 1:1 2A 800V TPS92314 CCOMP 4.7 F DOUT 1A 600V RF 120Q RISNS 0.4Q Figure 25. Non-isolated Topology Schematic Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A Submit Documentation Feedback 19 TPS92314 TPS92314A SNVS856B – JUNE 2012 – REVISED MAY 2013 www.ti.com REVISION HISTORY Changes from Revision A (May 2013) to Revision B • 20 Page Changed layout of National Data Sheet to TI format .......................................................................................................... 19 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links: TPS92314 TPS92314A PACKAGE OPTION ADDENDUM www.ti.com 28-Aug-2013 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish (2) MSL Peak Temp Op Temp (°C) Device Marking (3) (4/5) TPS92314AD/NOPB ACTIVE SOIC D 8 95 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 T92314 A TPS92314ADR/NOPB ACTIVE SOIC D 8 2500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 T92314 A TPS92314D/NOPB ACTIVE SOIC D 8 95 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 T92314 TPS92314DR/NOPB ACTIVE SOIC D 8 2500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 T92314 (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. 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Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 8-May-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device TPS92314DR/NOPB Package Package Pins Type Drawing SOIC D 8 SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) 2500 330.0 12.4 Pack Materials-Page 1 6.5 B0 (mm) K0 (mm) P1 (mm) 5.4 2.0 8.0 W Pin1 (mm) Quadrant 12.0 Q1 PACKAGE MATERIALS INFORMATION www.ti.com 8-May-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) TPS92314DR/NOPB SOIC D 8 2500 367.0 367.0 35.0 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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