TPS92560 www.ti.com SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 SIMPLE LED DRIVER FOR MR16 AND AR111 APPLICATIONS Check for Samples: TPS92560 FEATURES APPLICATIONS • • • • 1 • • • • • • • • • • • Controlled peak input current to prevent overstressing of the electronic transformer Allows either step-up or step-up/down operation Compatible to generic electronic transformers Compatible to magnetic transformers and DC power supplies Integrated active low-side input rectifiers Compact and simple circuit >85% efficiency (12VDC input) Power factor > 0.9 (full load with AC input) Hysteretic control scheme Output Over-Voltage Protection Over-temperature Shutdown 10-pin mini SOIC package with exposed pad MR16/AR111 LED lamps Lighting system using electronic transformer General lighting systems that require a boost / SEPIC LED driver DESCRIPTION The TPS92560 is a simple LED driver designed to drive high power LEDs by drawing constant current from the power source. The device is ideal for MR16 and AR111 applications which need good compatibility to DC and AC voltages and electronic transformers. The hysteretic control scheme does not need control loop compensation while providing the benefits of fast transient response and high power factor. The patent pending feedback control method allows the output power to be determined by the number of LED used without component change. The TPS92560 supports both boost and SEPIC configurations for the use of different LED modules. TYPICAL APPLICATION L1 D3 LED CIN RADJ1 COUT Q1 TPS92560 GATE RADJ2 CADJ CVCC RSEN R1 D1 D2 AC1 SRC PGND VCC AC2 SEN VP GND ADJ Power Source CVP Typical application circuit of the TPS92560 using boost configuration 1 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. 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 TPS92560 SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 www.ti.com TYPICAL APPLICATION (Continue) D3 L1 C1 LED CIN RADJ1 COUT L2 Q1 TPS92560 GATE RADJ2 CADJ CVCC RSEN R1 D1 D2 AC1 SRC PGND VCC AC2 SEN VP GND ADJ Power Source CVP D4 Typical Application Circuit of the TPS92560 using SEPIC configuration 2 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 TPS92560 www.ti.com SNVS900A – DECEMBER 2012 – REVISED JANUARY 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. BLOCK DIAGRAM TPS92560 VP VCC VCC LDO AC1 TSD TJ=165°C GATE DRIVER GATE AC2 UVLO VCC < 4.98V SRC Main Switch and Rectifier Control Logic SEN GND ADJ VCC VCC DRV DRV OVP 0.384V PGND SVA-30207403 ORDERING INFORMATION ORDER NUMBER TPS92560DGQ TPS92560DGQR PACKAGE TYPE 10L MINI SOIC EXP PAD NSC PACKAGE DRAWING MUC10A SUPPLIED AS 1000 Units on Tape and Reel 4500 Units on Tape and Reel Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 3 TPS92560 SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 www.ti.com 10-pin mini SOIC Package (TOP VIEW) GATE AC1 er AC2 SEN Po w VCC PGND PA D SRC VP GND ADJ Package Number MUC10A SVA-30207405 TERMINAL FUNCTIONS PIN DESCRIPTION APPLICATION INFORMATION NO. NAME 1 GATE Gate driver output pin Connect to the Gate terminal of the low-side N-channel Power FET 2 SRC Gate driver return Connect to the Source terminal of the low-side N-channel Power FET 3 VCC VCC regulator output Connect 0.47μF decoupling cap from this pin to SRC pin 4 SEN Current sense pin Kelvin-sense current sensing input. Should connect to the current sensing resistor, RSEN. 5 GND Analog ground Reference point for current sensing. 6 ADJ LED current adjust pin Connect to resistor divider from LED top voltage rail to set LED current 7 VP Power supply of the IC Connect it to the LED top voltage rail (for boost) or Connect it through a diode from LED top voltage rail (for SEPIC) 8 AC2 Power return terminal Connect to AC or DC input terminal 9 PGND Power ground Connect to system ground plane 10 AC1 Power return terminal Connect to AC or DC input terminal PowerPAD Thermal DAP Connect to system ground plane for heat dissipation ABSOLUTE MAXIMUM RATINGS (1) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications. ESD Rating TJ (1) (2) 4 VALUE UNIT SRC, SEN, ADJ –0.3 to 5 V AC1, AC2 –1 to 45 V VP –0.3 to 45 V VCC –0.3 to 12 V Human Body Model (2) 1.5 kV Storage Temperature –65 to +150 °C Junction Temperature –40 to +125 °C Absolute Maximum Ratings are limits which damage to the device may occur. Operating ratings are conditions under which operation of the device is intended to be functional. For specified specifications and test conditions, see the electrical characteristics. The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 TPS92560 www.ti.com SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 RECOMMENDED OPERATING CONDITIONS over operating free-air temperature range (unless otherwise noted) MIN NOM MAX UNIT VP Supply voltage range 6.5 42 V TJ Junction temperature range –40 125 °C θJA (1) Thermal resistance, Junction to Ambient, 0 LFPM Air Flow 48 °C/W θJC (1) Thermal resistance, Junction to Case 10 °C/W (1) θJA and θJC measurements are performed on JEDEC boards in accordance with JESD 51-5 and JESD 51-7 ELECTRICAL CHARACTERISTICS Specification with standard type are for TA=TJ= 25°C only; limits in boldface type apply over the full Operating Junction Temperature (TJ) range. Minimum and Maximum are specified through test, design or statistical correlation. Typical values represent the most likely parametric norm at TJ= 25°C, and are provided for reference purposes only. Unless otherwise stated the following conditions apply: VVP = 12V PARAMETER TEST CONDITIONS MIN TYP MAX UNIT 0.7 1.4 1.95 mA ICC ≤ 10mA, CVCC =0.47µF 12V < VVP < 42V 7.82 8.45 9.08 ICC = 10mA, CVCC =0.47µF VVP = 6.5V 5.22 5.8 6.18 ICC = 0mA, CVCC =0.47µF VVP = 2V 1.96 2.0 SUPPLY IIN VIN Operating current 6.5 V < VVP < 42 V VCC REGULATOR VCC VCC Regulated Voltage ICC-LIM VCC Current Limit VCC-UVLO-UPTH (1) VCC = 0V 6.5V < VVP < 42V V 21 30 39 VCC UVLO Upper Threshold 5.0 5.38 5.76 mA VCC-UVLO-LOTH VCC UVLO Lower Threshold 4.63 4.98 5.33 V VCC-UVLO-HYS VCC UVLO Hysteresis 190 400 640 mV V MOSFET GATE DRIVER VGATE-HIGH Gate Driver Output High w.r.t. SRC Sinking 100mA from GATE Force VCC = 8.5V 7.61 8.1 8.5 V VGATE-LOW Gate Driver Output Low w.r.t. SRC Sourcing 100mA to GATE 100 180 290 mV tRISE VGATE Rise Time CGATE = 1nF across GATE and SRC 22 ns tFALL VGATE Fall Time CGATE = 1nF across GATE and SRC 14 ns tRISE-PG-DELAY VGATE Low to High Propagation Delay CGATE = 1nF across GATE and SRC 68 ns tFALL-PG-DELAY VGATE High to Low Propagation Delay CGATE = 1nF across GATE and SRC 84 ns CURRENT SOURCE AT ADJ PIN IADJ-STARTUP Output Current of ADJ pin at Startup VADJ = 0V IADJ-ELEC-XFR Output Current of ADJ pin for Electronic An Electronic Transformer is Detected Transformers IADJ-MAG-XFR Output Current of ADJ pin for Inductive Transformers An Magnetic Transformer is Detected 16 20 24 µA 8 11.5 15 µA 7 9.5 12 µA 8.9 14.9 20.9 mV –20.6 –14.9 –8.8 mV CURRENT SENSE COMPARATOR VSEN-UPPER-TH VSEN Upper Threshold Over VADJ VSEN-VADJ, VADJ=0.2V, VGATE at falling edge VSEN-LOWER-TH VSEN Lower Threshold Over VADJ VSEN-VADJ, VADJ=0.2V VGATE at rising edge VSEN-HYS VSEN Hysteresis (VSEN-UPPER-TH - VSEN-LOWER-TH) 22.5 29.8 37.5 mV VSEN-OFFSET VSEN Offset w.r.t. VADJ (VSEN-UPPER-TH + VSEN-LOWER-TH)/2 –3.5 0.02 3.5 mV 300 570 mΩ ACTIVE low-side input rectifiers RACn-ON (1) In resistance of AC1 and AC2 to GND IACn = 200mA VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading. Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 5 TPS92560 SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 www.ti.com ELECTRICAL CHARACTERISTICS (continued) Specification with standard type are for TA=TJ= 25°C only; limits in boldface type apply over the full Operating Junction Temperature (TJ) range. Minimum and Maximum are specified through test, design or statistical correlation. Typical values represent the most likely parametric norm at TJ= 25°C, and are provided for reference purposes only. Unless otherwise stated the following conditions apply: VVP = 12V PARAMETER TEST CONDITIONS MIN TYP MAX UNIT VACn-ON-TH Turn ON Voltage Threshold of AC1 and AC2 VACn Decreasing 36 52 67 mV VACn-OFF-TH Turn OFF Voltage Threshold of AC1 and AC2 VACn Increasing 77 90 104 mV VACn-TH-HYS Hysteresis Voltage of AC1 and AC2 VACn-OFF-TH - VACn-ON-TH 39 IACn-OFF Off Current of AC1 and AC2 VACn = 45V 21 32 µA mV OUTPUT OVER-VOLTAGE-PROTECTION (OVP) VADJ-OVP-UPTH Output Over-Voltage-Detection Upper Threshold VADJ Increasing, VGATE at falling edge 0.353 0.384 0.415 V VADJ-OVP-LOTH Output Over-Voltage-Detection Lower Threshold VADJ Decreasing, VGATE at rising edge 0.312 0.339 0.366 V VADJ-OVP-HYS Output Over-Voltage-Detection Hysteresis VADJ-OVP-UPTH - VADJ-OVP-LOTH 25 46 67 mV THERMAL SHUTDOWN TSD Thermal Shutdown Temperature TJ Rising 165 °C TSD-HYS Thermal Shutdown Temperature Hysteresis TJ Falling 30 °C 6 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 TPS92560 www.ti.com SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 TYPICAL CHARACTERISTICS All curves taken for the boost circuit are with 500mA nominal input current and 6 serial LEDs. All curves taken for the SEPIC circuit are with 500mA nominal input current and 3 serial LEDs.TA = –40°C to 125°C, unless otherwise specified. Operation Current vs. Temperature VCC vs. Temperature (ICC = 0mA) 8.45 VVP=42V 1.5 8.4 VVP=42V 1.4 8.35 1.3 VCC (V) Operation Current, IIN (mA) 1.6 VVP=12V 1.2 VVP=12V 8.25 VVP=6.5V 1.1 8.2 1 8.15 -40 -20 0 20 40 60 80 100 120 Ambient Temperature, TA (ƒC) 140 -40 -20 0 20 60 80 100 120 140 C002 Figure 1. Figure 2. VCC UVLO Rising Threshold vs. Temperature VVP=12V, GATE='Hi' VCC UVLO Falling Threshold vs. Temperature VVP=12V, GATE='Low' VCC UVLO Falling Threshold (V) 5.02 5.4 5.38 5.36 5.34 5.32 5.3 5 4.98 4.96 4.94 4.92 -40 -20 0 20 40 60 80 100 120 Ambient Temperature, TA (ƒC) 140 -40 -20 0 20 40 60 80 100 120 Ambient Temperature, TA (ƒC) C003 Figure 3. 140 C004 Figure 4. ACn Turn OFF Threshold vs. Temperature ACn Turn ON Threshold vs. Temperature 80 ACn Turn ON Threshold (mV) 140 ACn Turn OFF Threshold (mV) 40 Ambient Temperature, TA (ƒC) C001 5.42 VCC UVLO Rising Threshold (V) 8.3 120 100 80 60 40 70 60 50 40 30 -40 -20 0 20 40 60 80 Temperature, TA (ƒC) 100 120 140 -40 C005 Figure 5. -20 0 20 40 60 80 100 120 Ambient Temperature, TA (ƒC) 140 C006 Figure 6. Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 7 TPS92560 SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 www.ti.com TYPICAL CHARACTERISTICS (continued) All curves taken for the boost circuit are with 500mA nominal input current and 6 serial LEDs. All curves taken for the SEPIC circuit are with 500mA nominal input current and 3 serial LEDs.TA = –40°C to 125°C, unless otherwise specified. Output Current (BOOST) vs. Temperature Output Current (SEPIC) vs. Temperature 0.7 0.9 0.8 Output Current, IOUT (A) Output Current, IOUT (A) 0.6 0.5 VIN=12V 0.4 0.3 0.2 0.1 0.7 0.6 VIN=12V 0.5 0.4 0.3 0.2 0.1 0 0 -40 -20 0 20 40 60 80 100 120 Ambient Temperature, TA (ƒC) 140 -40 -20 0 20 Figure 7. Output Power (BOOST) vs. Temperature 100 120 140 C008 Output Power (SEPIC) vs. Temperature Output Power, POUT (W) Output Power, POUT (W) 80 10 10 8 VIN=12V 6 4 2 0 8 6 VIN=12V 4 2 0 -40 -20 0 20 40 60 80 100 120 Ambient Temperature, TA (ƒC) 140 -40 -20 0 20 40 60 80 100 120 Ambient Temperature, TA (ƒC) C009 Figure 9. 140 C010 Figure 10. Efficiency (BOOST) vs. Temperature Efficiency (SEPIC) vs. Temperature 100 100 VIN=18V VIN=15V VIN=18V VIN=15V 90 Efficiency (%) 90 Efficiency (%) 60 Figure 8. 12 80 VIN=12V 70 VIN=9V 80 VIN=12V 70 VIN=6V VIN=9V 60 VIN=6V 60 50 50 -40 -20 0 20 40 60 80 100 Ambient Temperature, TA (ƒC) 120 140 -40 C011 Figure 11. 8 40 Ambient Temperature, TA (ƒC) C007 -20 0 20 40 60 80 100 Ambient Temperature, TA (ƒC) 120 140 C012 Figure 12. Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 TPS92560 www.ti.com SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 OVERVIEW The TPS92560 is a simple hysteretic control switching LED driver for MR16 or AR111 lighting applications. The device accepts DC voltage, AC voltage and electronic transformer as an input power source. The compact application circuit can fit into a generic case of MR16 lamps easily. The hysteretic inductor current control scheme requires no small signal control loop compensation and maintains constant average input current to secure high compatibility to different kinds of input power source. The TPS92560 can be configured to either a step-up or step-up/down LED driver for the use of different number of LEDs. The patent pending current control mechanism allows the use of a single set of component and PCB layout for serving different output power requirements by changing the number of LEDs. The integrating of the active low-side input rectifiers reduces the power loss for voltage rectification and saves two external diodes of a generic bridge rectifier to aim for a simple end application circuit. When the driver is used with an AC voltage source or electronic transformer, the current regulation level increases accordingly to maintain an output current close to the level that when it is used with a DC voltage source. With the output over-voltage protection and over-temperature shutdown functions, the TPS92560 is specifically suitable for the applications that are space limited and need wide acceptance to different power sources. VCC REGULATOR The VCC pin is the output of the internal linear regulator for providing an 8.45V typical supply voltage to the MOSFET driver and internal circuits. The output current of the VCC pin is limited to 30mA typical. A low ESR ceramic capacitor of 0.47μF or higher capacitance should be connected across the VCC and SRC pins to supply transient current to the MOSFET driver. MOSFET DRIVER The GATE pin is the output of the gate driver which referenced to the SRC pin. The gate driver is powered directly by the VCC regulator which the maximum gate driving current is limited to 30mA typical. To prevent hitting the VCC current limit, it is suggested to use a low gate charge MOSFET when high switching frequency is needed. THE ADJ PIN The voltage on the ADJ pin determines the reference voltage for the input current regulation. Typically, the ADJ pin voltage is divided from the output voltage of the circuit by a voltage divider, thus the average input current is adjusted with respect to the number of LEDs used. The voltage of the ADJ pin determines the input current following the expression: IIN(nom) = RADJ2 VVP x RSEN RADJ1 + RADJ2 (1) Output Over-Voltage-Protection In the TPS92560, a function of output Over-Voltage Protection (OVP) is provided to prevent damaging of the circuit due to an open circuit of the LED. The OVP function is implemented to the ADJ pin. When the voltage of the ADJ pin exceeds 0.384V typical, the OVP circuit disables the MOSFET driver and turns off the main switch to allow the output capacitor to discharge. As the voltage of the ADJ pin decreases to below 0.353V typical, the MOSFET driver is enabled and the TPS92560 returns to normal operation. The triggering threshold of the output voltage is determined by the value of the resistors RADJ1 and RADJ2, which can be calculated using the following equation: VVP x RADJ2 ≤ 0.384V RADJ1 + RADJ2 (2) When defining the OVP threshold voltage, it is necessary to certain that the OVP threshold voltage does not exceed the rated voltage of the output rectifier and capacitor to avoid damaging of the circuit. Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 9 TPS92560 SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 www.ti.com THE AC1 AND AC2 PINS The TPS92560 provides two internal active rectifiers for input voltage rectification. Each internal rectifier connects across the ACn pin to GND. These internal active rectifiers function as the low-side diode rectifiers of a generic bridge rectifier. The integrating of the active rectifiers helps in saving two external diodes of a bridge rectifier along with an improvement of power efficiency. For high power applications, for instance, 12W output power, external diode rectifiers can be added across the ACn pin to GND to reduce heat dissipation on the TPS92560. DETECTION OF POWER SOURCE VIN (From elect. transformer) 12V × 2 Time 0 Dead time Switching period of the elect. transformer 1/50Hz or 1/60Hz Figure 13. The inherent dead time of the output voltage of an electronic transformer Both the voltages of a generic AC source (50/60Hz) and an electronic transformer carry certain amount of dead time inherently, as shown in Figure 13. The existing of the dead time leads to a drop of the RMS input power to the driver circuit. In order to compensate the drop of the RMS input power, the ADJ pin sources current to the resistor, RADJ2 to increase the reference voltage for the current regulation loop and in turn increase the RMS input power accordingly when an AC voltage source or electronic transformer is detected. The output current of the ADJ pin for an AC input voltage and electronic transformer are 9.5μA and 11.5μA typical respectively. Practically the amount of the power for compensating the dead time of the input power source differs case to case depending on the characteristics of the power source, the value of the RADJ1 and RADJ2 might need a fine adjustment in accordance to the characteristics of the power source. The additional output power for compensating the dead time of the power sources (ΔPLED) are calculated using the following equations: For 50/60Hz AC power source: R ´ 9.5 mA DPLED -50/60 Hz = VIN ´ ADJ2 ´h RSEN (3) For electronic transformer: DPLED-ELECT - XFR = VIN ´ R ADJ2 ´ 11.5 mA ´h RSEN (4) CURRENT REGULATION In the TPS92560, the input current regulation is attained by limiting the peak and valley of the inductor current. Practically the inductor current sensing is facilitated by detecting the voltage on the resistor, RSEN. Because the current flows through the RSEN is a sum total of the currents of the main switch and LEDs, the voltage drop on the RSEN reflects the current of the inductor that is identical to the input current to the LED driver circuit. Figure 14 shows the waveform of the inductor current ripple with the peak and valley values controlled. 10 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 TPS92560 www.ti.com SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 IL tON IL(peak) tOFF Switch off VSEN-UPPER-TH RSEN Time VSEN-LOWER-TH RSEN IL(valley) Switch on tFALL-PG-DELAY tRISE-PG-DELAY SVA-30207404 Figure 14. Inductor Current Ripple in Steady State The voltage of the ADJ pin is determined by the forward voltage of the LED and divided from the VVP by a resistor divider. The equation for calculating the VADJ as shown in the following expression: R ADJ2 VADJ = VVP ´ R ADJ1 + R ADJ2 (5) In steady state, the voltage drop on the RADJ1 is identical to the forward voltage of the LED (VLED) and the voltage across the RADJ2 is identical to the voltage across the RSEN. The LED current, ILED is then calculated following the equations: In steady state: VLED = VRADJ1 VSEN = VRADJ2 VSEN IIN(nom) = RSEN Since PLED = PIN x η (6) (7) (8) where η is the conversion efficiency (9) Thus, VLED x ILED = VIN x IIN(nom) x η (10) Put the expressions (2) to (4) into (5): IADJ2 x RADJ2 x η ILED = VIN x IADJ1 x RADJ1 x RSEN (11) Due to the high input impedance of the ADJ pin, the current flows into the ADJ pin can be neglected and thus IRADJ1 equals IRADJ2. The LED current is then calculated following the expressions below: RADJ2 x η ILED = VIN x RADJ1 x RSEN (12) Practically, the conversion efficiency of a boost circuit is almost a constant around 85%. Being assumed that the efficiency term in the ILED expression is a constant, the LED current depends solely on the magnitude of the input voltage, VIN. Without changing a component, the output power of the typical application circuits of the TPS92560 is adjustable by using different number of LEDs. The output power is calculated by following the expression: RADJ2 x η PLED = VLED x VIN x RADJ1 x RSEN (13) Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 11 TPS92560 SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 www.ti.com SWITCHING FREQUENCY (Boost Configuration) In the following sections, the equations and calculations are limited to the boost configuration only (i.e. the LED forward voltage higher than the input voltage), unless otherwise specified. The application information for the SEPIC and other circuit topologies are available in separate application notes and reference designs. In the boost configuration, including the propagation delay of the control circuit, the ON and OFF times of the main switch are calculated following the expressions: tON = tOFF = VSEN-UPPER-TH x L RSEN x [VIN - VD - IIN(nom) x (RL + RDS(ON) +RSEN + RAC-FET)] VSEN-LOWER-TH x L + tFALL-PG-DELAY (14) + tRISE-PG-DELAY RSEN x [VLED - VIN - 2VD - IIN(nom) x (RL +RSEN + RAC-FET)] x 2 x 2 (15) In the above equations, the VD is the forward voltage of D3, RL is the DC resistance of L1, RDS(ON) is the ON resistance of Q1 and RAC-FET is the turn ON resistance of the internal active rectifier with respect to the typical application circuit diagram. Practically the resistance of the RL, RDS(on) and RAC-FET is in the order if serveral tenth of mΩ, by assuming a 0.5V diode forward voltage and the sum total of the RL, RDS(ON) and RAC-FET is close to 1Ω, the on and off times of Q1 can be approximated using the following equations: tON ≈ tOFF ≈ 14.9mV x L RSEN x [VIN – 0.5V - IIN(nom) x (1 + RSEN)] + 84ns 14.9mV x L RSEN x [VLED - VIN - 1V - IIN(nom) x (1 + RSEN)] x 2 (16) + 68ns x 2 (17) With the switching on and OF times determined, the switching frequency can be calculated using the following equation: 1 fSW = t ON + t OFF (18) Because of the using of hysteretic control scheme, the switching frequency of the TPS92560 in steady state is dependent on the input voltage, output voltage and inductance of the inductor. Generally a 1 MHz to 1.5 MHz switching frequency is suggested for applications using an electronic transformer as the power source. INDUCTOR SELECTION (Boost Configuration) Because of the using of the hysteretic control scheme, the switching frequency of the TPS92560 in a boost configuration can be adjusted in accordance to the value of the inductor being used. Derived from the equations (12) and (13), the value of the inductor can be determined base on the desired switching frequence by using the following equation: 1 − 304ns × R SEN fSW L= 1 1 × 29 .8mV + VIN − 0.5 V − IIN(nom) × (1 + R SEN ) VLED − VIN − 1V − IIN(nom) × (1 + R SEN ) (19) When selecting the inductor, it is essential to ensure the peak inductor current does not exceed the the factory suggested saturation current of the inductor. The values of the peak and valley inductor current are calculated using the following equations: Peak inductor current: [VIN - VD - IIN(nom) x (RL + RDS(ON) +RSEN + RAC-FET)] x tON IL(peak) = 2L + IIN(nom) (20) Valley inductor current: 12 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 TPS92560 www.ti.com SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 IL(valley) = IIN(nom) - [VLED - VIN - 2VD - IIN(nom) x (RL +RSEN + RAC-FET)] x tOFF 2L (21) Assume the total resistance of the RL, RDS(on) and RAC-FET is 1Ω and the diode drop, VD equal to 1V, the peak and valley currents of the inductor can be approximated using the following equations: [VIN – 0.5V - IIN(nom) x (1 + RSEN)] x tON IL(peak) ≈ + IIN(nom) 2L (22) [VLED - VIN - 1V - IIN(nom) x (1 + RSEN)] x tOFF IL(valley) ≈ IIN(nom) 2L (23) In order not to saturate the inductor, an inductor with a factory guranteed saturation current (ISAT) 20% higher than the IL(peak) is suggested. Thus the ISAT of the inductor should fulfill the following requirement: ISAT ≥ IL(peak) x 1.2 (24) THERMAL SHUTDOWN The TPS92560 includes a thermal shutdown circuitry that ceases the operation of the device to avoid permanent damage. The threshold for thermal shutdown is 165°C with a 30°C hysteresis typical. During thermal shutdown the VCC regulator is disabled and the MOSFET is turned off. INPUT SURGE VOLTAGE PROTECTION When use with an electronic transformer, the surge voltage across the input terminals can be sufficiently high to damage the TPS92560 depending on the charactistics of the electronic transformer. To against potential damaging due to the input surge voltage, a 36V zener diode can be connected across the input bridge rectifier as shown in Figure 15. L1 36V Zener Diode U1 TPS92560 CIN R1 D1 D2 AC1 PGND Power Source AC2 Figure 15. Input surge voltage protection using an external zener diode Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 13 TPS92560 SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 www.ti.com EXAMPLE APPLICATION CIRCUITS In the applications that need true regulation of the LED current, the intrinsic input current control loop can be changed to monitor the LED current by adding an external LED current sensing circuit. Figure 16 and Figure 19 show the example circuits for true LED current regulation in boost and SEPIC configurations respectively. In the circuits, the U3 (TL431) maintains a constant 2.5V voltage drop on the resistors, R3 and R7. Because the U2 (TL431) maintains a constant voltage drop on the R3, the power dissipation on the output current sensing resistor, R7 can be minimized by setting a low voltage drop on the R7. Because the change of the current flowing through the R7 reflects in the change of the cathode current of U3 and eventually adjusts the ADJ pin voltage of the TPS92560, the LED current is regulated independent of the change of the input voltage. Boost Application Circuit with LED Current Regulation The specifications of the boost application circuit in Figure 16 are as listed below: • Objective input voltage: 3VDC to 18VDC / 12VAC(50Hz or 60Hz) / Generic MR16 electronic transformer • LED forward voltage: 20VDC typical • Output current: 300mA typical (@12VDC input) • Output power: 6W typical (@12VDC input) L1 15µH D3 2A 40V LED VCC R5 15k R2 4.02k R4 562 U2 TL431 R7 1 U3 C1 1µF R3 4.02k TL431 COUT1 35V 330µF R6 40.2k COUT 1µF CVCC 4.7µF 1µF CIN 25V 1µF R1 105 VCC Q1 3A 60V CADJ RADJ2 1k Z1 36V TPS92560 GATE RSEN 0.2 D1 2A 40V D2 2A 40V AC1 SRC PGND VCC AC2 SEN VP GND ADJ Power Source CVP 47nF U1 Figure 16. Using the TPS92560 in SEPIC configuration with LED current regulation Typical Characteristics of the Boost Example Circuit in Figure 16 All curves taken at VIN = 3V to 18VDC in boost configuration, with 300mA nominal output current, 6 serial LEDs. TA = 25°C. Efficiency vs. Input Voltage 100 300 90 80 250 Efficiency (%) LED Current, ILED (mA) LED Current vs. Input Voltage 350 200 150 70 60 50 100 40 50 30 0 2 4 6 8 10 12 Input Voltage, VIN (V) 14 16 18 20 0 C017 Figure 17. 14 2 4 6 8 10 12 Input Voltage, VIN (V) 14 16 18 20 C018 Figure 18. Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 TPS92560 www.ti.com SNVS900A – DECEMBER 2012 – REVISED JANUARY 2013 SEPIC Application Circuit with LED Current Regulation The specifications of the SEPIC application circuit in Figure 16 are as listed below: • Objective input voltage: 3VDC to 18VDC / 12VAC(50Hz or 60Hz) / Generic MR16 electronic transformer • LED forward voltage: 13VDC typical • Output current: 300mA typical (@12VDC input) • Output power: 4W typical (@12VDC input) C2 1µF D3 2A 40V L1 15µH LED VCC R5 1.82k R2 4.02k R4 562 U2 TL431 U3 TL431 C1 1µF R3 4.02k R7 1 R6 36.5k RADJ2 1k Z1 36V COUT1 25V 330µF COUT 4.7µF L2 15µH CIN 25V 1µF R1 105 VCC Q1 3A 60V CADJ CVCC 4.7µF 1µF D1 2A 40V TPS92560 GATE RSEN 0.3 D2 2A 40V AC1 SRC PGND VCC AC2 SEN VP GND ADJ Power Source CVP 100nF U1 D4 600mA 40V Figure 19. Using the TPS92560 in SEPIC configuration with LED current regulation Typical Characteristics of the SEPIC Example Circuit in Figure 19 All curves taken at VIN = 3V to 18VDC in SEPIC configuration, with 300mA nominal output current, 4 serial LEDs. TA = 25°C. Efficiency vs. Input Voltage 100 300 90 80 250 Efficiency (%) LED Current, ILED (mA) LED Current vs. Input Voltage 350 200 150 70 60 50 100 40 50 30 0 2 4 6 8 10 12 14 Input Voltage, VIN (V) 16 18 20 0 C019 Figure 20. 2 4 6 8 10 12 14 16 18 Input Voltage, VIN (V) 20 C020 Figure 21. Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Product Folder Links :TPS92560 15 PACKAGE OPTION ADDENDUM www.ti.com 24-Jan-2013 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Qty Drawing Eco Plan Lead/Ball Finish (2) MSL Peak Temp Op Temp (°C) Top-Side Markings (3) (4) TPS92560DGQ/NOPB ACTIVE MSOPPowerPAD DGQ 10 1000 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 85 SN3B TPS92560DGQR/NOPB ACTIVE MSOPPowerPAD DGQ 10 3500 Green (RoHS & no Sb/Br) CU SN Level-3-260C-168 HR -40 to 85 SN3B (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) Only one of markings shown within the brackets will appear on the physical device. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. 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