A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Description Pin Assignments NEW PRODUCT The ZXLD1374 is a 60V LED driver with integrated 1.5A low side switch to drive high current LEDs. It is a multi-topology converter enabling it to operate in Buck, Boost and Buck-boost configurations; efficiently controlling the current of up to 16 series connected LEDs. The ZXLD1374 is a modified hysteretic converter using a patent pending control scheme providing high output current accuracy in all three topologies. High accuracy dimming is achieved through DC control and high frequency PWM control. The ZXLD1374 uses two pins for fault diagnosis. A flag output highlights a fault, while the multi-level status pin gives further information on the exact fault. TSSOP-20EP ADJ 1 20 GI REF 2 19 PWM TADJ 3 18 FLAG SHP 4 17 ISM STATUS 5 16 VIN SGND 6 15 VAUX PGND 7 14 LX PGND 8 13 LX N/C 9 12 N/C 11 N/C N/C 10 Thermal Pad ZXLD1374 The ZXLD1374 has been qualified to AEC-Q100 Grade 1 enabling operation in ambient temperatures from -40 to 125°C. Features • • • • • • • • • 0.5% typical output current accuracy 6.3 to 60V operating voltage range 1.5A integrated low side switch LED driver supports Buck, Boost and Buck-Boost topologies Wide dynamic range dimming o 20:1 DC dimming o 1000:1 dimming range at 500Hz Up to 1MHz switching High temperature control of LED current using TADJ AEC-Q100 Grade 1 Available in “Green” Molding Compound (No Br, Sb) with lead Free Finish/ RoHS Compliant (Note 1) Note 1: EU Directive 2002/95/EC (RoHS). All applicable RoHS exemptions applied. Please visit our website at http://www.diodes.com/products/lead_free.html Typical Application Circuit ZXLD1374 Document number: DS35032 Rev. 2 - 2 1 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Pin Descriptions NEW PRODUCT Pin Name Pin Type (Note 2) ADJ 1 I REF 2 O TADJ 3 I SHP 4 I/O STATUS 5 O SGND 6 P PGND 7,8 P LX 9, 10, 11, 12 13, 14 O VAUX 15 P VIN 16 P ISM 17 I FLAG 18 O PWM 19 I GI 20 I EP PAD P N/C Notes: - Description Adjust input (for dc output current control) Connect to REF to set 100% output current. Drive with dc voltage (125mV<VADJ< 2.5V) to adjust output current from 10% to 200% of set value. The ADJ pin has an internal clamp that limits the internal node to less than 3V. This prevents the LED and power switch from delivering too much current should ADJ get overdriven. Internal 1.25V reference voltage output Temperature Adjust input for LED thermal current control Connect thermistor/resistor network to this pin to reduce output current above a preset temperature threshold. Connect to REF to disable thermal compensation function (See section on thermal control). Shaping capacitor for feedback control loop Connect 100pF ±20% capacitor from this pin to ground to provide loop compensation Operation status output (analog output) Pin is at 4.5V (nominal) during normal operation. Pin switches to a lower voltage to indicate specific operation warnings or fault conditions (See section on STATUS output). Status pin voltage is low during shutdown mode. Signal ground Connect to 0V and pins 7 and 8. Power ground Connect to 0V and pin 6 to maximize copper area. Not Connected internally To maximize PCB copper for thermal dissipation connect to pins 7 and 8. Low-side power-switch output Auxiliary positive supply to internal switch gate driver Connect to VIN, or auxiliary supply from 6V to 15V supply to reduce internal power dissipation (Refer to application section for more details). Decouple to ground with capacitor close to device (refer to Applications section). Input supply to device (6.3V to 60V) Decouple to ground with capacitor close to device (refer to Applications section). Current monitor input Connect current sense resistor between this pin and VIN. The nominal voltage across the resistor is 225mV. Flag open drain output Pin is high impedance during normal operation. Pin switches low to indicate a fault, or warning condition. Digital PWM output current control Pin driven either by open Drain or push-pull 3.3V or 5V logic levels. Drive with frequency higher than 100Hz to gate output ‘on’ and ‘off’ during dimming control. The device enters standby mode when PWM pin is driven with logic low level for more than 15ms nominal (Refer to application section for more details). Gain setting input Used to set the LED current in Boost and Buck-boost modes. Connect to ADJ in Buck mode operation. For Boost and Buck-boost modes, connect to resistive divider from ADJ to SGND. This defines the ratio of switch current to LED current (see application section). The GI pin has an internal clamp that limits the internal node to less than 3V. This provides some failsafe should the GI pin get overdriven. Exposed paddle. Connect to 0V plane for electrical and thermal management. 2. Type refers to whether or not pin is an Input, Output, Input/Output or Power supply pin. ZXLD1374 Document number: DS35032 Rev. 2 - 2 2 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated) Symbol VIN VAUX NEW PRODUCT VISM VSENSE Parameter Input supply voltage relative to GND ‡ Auxiliary supply voltage relative to GND‡ Current monitor input relative to GND ‡ Current monitor sense voltage (VIN-VISM) ‡ VLX Low side switch output voltage to GND ILX Low side switch continuous output current ISTATUS VFLAG VPWM, VADJ, VTADJ, VGI TJ TST Status pin output current Rating Unit -0.3 to 65 V -0.3 to 65 V -0.3 to 65 V -0.3 to 5 V -0.3 to 65 V 1.8 A ±1 mA Flag output voltage to GND (Note 3) -0.3 to 40 V Other input pins to GND (Note 3) -0.3 to 5.5 V 150 °C -55 to 150 °C Maximum junction temperature Storage temperature These are stress ratings only. Operation outside the absolute maximum ratings may cause device failure. Operation at the absolute maximum rating for extended periods may reduce device reliability. Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when handling and transporting these devices. Notes: 3. For correct operation SGND and PGND should always be connected together. Package Thermal Data Thermal Resistance Package Junction-to-Ambient, θJA (Note 4) TSSOP-20EP Junction-to-Case, θJC Note: Unit 28 °C/W 4 °C/W 4 Measured on High Effective Thermal Conductivity Test Board" according JESD51. ZXLD1374 Document number: DS35032 Rev. 2 - 2 3 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Recommended Operating Conditions Symbol NEW PRODUCT VIN VAUX Parameter Min Max Unit Input supply voltage range Normal operation Functional (Note 5) Performance/Comment 8 6.3 60 V Auxiliary supply voltage range (Note 6) Normal operation Functional 8 6.3 60 V 0 450 mV 60 V 1.5 A 2.5 V 100 µA VVIN-VISM, with 0 ≤ VADJ ≤ 2.5 VSENSE Differential input voltage VLX Low side switch output voltage ILX Low side switch continuous output current VADJ External dc control voltage applied to ADJ pin to adjust output current DC brightness control mode from 10% to 200% 0.125 ISTATUS Status pin output current IREF Reference external load current fSW Recommended switching frequency range (Note 7) VTADJ Temperature adjustment (TADJ) input voltage range fPWM REF sourcing current Recommended PWM dimming frequency range tPWMH/L PWM pulse width in dimming mode 0 VREF V 500 Hz To maintain 200:1 resolution 100 1000 Hz 0.005 10 ms 2 5.5 V VPWML PWM pin low level input voltage GI Gain setting ratio for Boost and Buck-boost modes Notes: kHz 100 PWM input high or low Operating Junction Temperature Range mA 1000 To maintain 1000:1 resolution VPWMH PWM pin high level input voltage TJ 1 300 Ratio= VGI/VADJ 0 0.4 V -40 125 °C 0.20 0.50 5. The functional range of VIN is the voltage range over which the device will function. Output current and device parameters may deviate from their normal values for VIN and VAUX voltages between 6.3V and 8V, depending upon load and conditions. 6. VAUX can be driven from a voltage higher than VIN to provide higher efficiency at low VIN voltages, but to avoid false operation; a voltage should not be applied to VAUX in the absence of a voltage at VIN. 7. The device contains circuitry to control the switching frequency to approximately 400kHz. The maximum and minimum operating frequency is not tested in production. ZXLD1374 Document number: DS35032 Rev. 2 - 2 4 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Electrical Characteristics Symbol (Test conditions: VIN = VAUX = 12V, TA = 25°C, unless otherwise specified.) Parameter Conditions Min Typ Max 5.2 5.6 6.3 5.5 6 6.5 Units NEW PRODUCT Supply and reference parameters VUV- Under-Voltage detection threshold Normal operation to switch disabled VIN or VAUX falling VUV+ Under-Voltage detection threshold Switch disabled to normal operation VIN or VAUX rising IQ-IN Quiescent current into VIN PWM pin floating. Output not switching IQ-AUX Quiescent current into VAUX ISB-IN Standby current into VIN. ISB-AUX Standby current into VAUX. PWM pin grounded for more than 15ms VREF Internal reference voltage No load Change in reference voltage with output current Sourcing 1mA ΔVREF VREF_LINE Reference voltage line regulation VREF-TC 1.237 V 1.5 3 mA 150 300 µA 90 150 µA 0.7 10 µA 1.25 1.263 V -5 Sinking 25µA VIN = VAUX , 6.5V<VIN = <60V V mV 5 -60 Reference temperature coefficient -90 dB +/-50 ppm/°C DC-DC converter parameters VADJ External dc control voltage applied to ADJ DC brightness control mode pin to adjust output current (Note 8) 10% to 200% IADJ ADJ input current (Note 8) VGI GI Voltage threshold for Boost and BuckVADJ = 1.25V boost modes selection (Note 8) IGI GI input current (Note 8) IPWM 0.125 1.25 2.5 V 100 5 nA µA 0.8 V 100 5 nA µA 36 100 µA 15 25 ms VADJ ≤ 2.5V VADJ = 5.0V VGI ≤ 2.5V VGI = 5.0V PWM input current VPWM = 5.5V PWM pulse width (to enter shutdown state) PWM input low TSDH Thermal shutdown upper threshold (LX output inhibited) Temperature rising. 150 ºC TSDL Thermal shutdown lower threshold (LX output re-enabled) Temperature falling. 125 ºC Measured into ISM pin and VISM = VIN 11 20 µA ±0.25 ±2 % 350 375 mV tPWMoff 10 High-Side Current Monitor (Pin ISM) IISM VSENSE_acc Input Current Accuracy of nominal VSENSE threshold voltage VADJ = 1.25V VSENSE-OC Over-current sense threshold voltage Notes: 300 8. The ADJ and GI pins have an internal clamp that limits the internal node to less than 3V. This limits the switch current should those pins get overdriven. ZXLD1374 Document number: DS35032 Rev. 2 - 2 5 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Electrical Characteristics (Test conditions: VIN = VAUX = 12V, TA = 25°C, unless otherwise specified.) Symbol Parameter Conditions Min Typ Max Units Output Parameters NEW PRODUCT VFLAGL FLAG pin low level output voltage IFLAGOFF FLAG pin open-drain leakage current VSTATUS STATUS Flag no-load output voltage (Note 9) RSTATUS Output impedance of STATUS output Output sinking 1mA VFLAG=40V 0.5 V 1 µA Normal operation 4.2 4.5 4.8 Out of regulation (VSHP out of range) (Note 10) 3.3 3.6 3.9 VIN under-voltage (VIN < 5.6V) 3.3 3.6 3.9 Switch stalled (tON or tOFF> 100µs) 3.3 3.6 3.9 LX over-voltage state (VLX >60V) 2.4 2.7 3.0 Over-temperature (TJ > 125°C) 1.5 1.8 2.1 Excess sense resistor current (VSENSE > 0.375V) 0.6 0.9 1.2 Excessive switch current (ISW>1.5A) 0.6 0.9 1.2 V Normal operation 10 kΩ Output stage off, VLX = 60V (Note 11) 60 µA ILX = 1.5A (tON < 100µs) 0.5 Low side switch output (LX pins tied together) ILX-LG Low side switch leakage current RDS(ON) LX pin MOSFET on resistance tPDHL Propagation delay high-low tPDLH Propagation delay low-high tLXR LX output rise time tLXF LX output fall time tSTALL Time to assert ‘STALL’ flag and warning on STATUS output (Note 12) VSENSE = 225mV ± 30%, CL = 680pF, RL = 120Ω LX low or high 0.8 Ω 86 ns 131 ns 208 ns 12 ns 100 170 µs LED Thermal control circuit (TADJ) parameters VTADJH Upper threshold voltage Onset of output current reduction (VTADJ falling) 560 625 690 mV VTADJL Lower threshold voltage Output current reduced to <10% of set value (VTADJ falling) 380 440 500 mV ITADJ TADJ pin Input current 1 µA VTADJ = 1.25V Notes: 9. In the event of more than one fault/warning condition occurring, the higher priority condition will take precedence. E.g. ‘Excessive coil current’ and ‘Out of regulation’ occurring together will produce an output of 0.9V on the STATUS pin. The voltage levels on the STATUS output assume the Internal regulator to be in regulation and VADJ<=VREF. A reduction of the voltage on the STATUS pin will occur when the voltage on VIN is near the minimum value of 6V. 10. Flag is asserted if VSHP<2.5V or VSHP>3.5V 11. With the device still in switching mode the LX pin has an over-voltage detection circuit connected to it with a resistance of approximately 1MΩ. 12. If tON exceeds tSTALL, LX turns off and then an initiate a restart cycle occurs. During this phase, ADJ is grounded internally and the SHP pin is switched to its nominal operating voltage, before operation is allowed to resume. Restart cycles will be repeated automatically until the operating conditions are such that normal operation can be sustained. If tOFF exceeds tSTALL, the switch will remain off until normal operation is possible. ZXLD1374 Document number: DS35032 Rev. 2 - 2 6 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 1500 900 2.5 1250 750 1000 600 2 LED Current (mA) 1.5 1 ILED Switching Frequency 500 150 0 6 0 1 1.5 2 2.5 ADJ Voltage (V) Figure 2. Buck LED Current, Switching Frequency vs. V ADJ 0 18 30 36 42 48 54 60 24 Supply Voltage (V) Figure 1. Supply Current vs. Supply Voltage 12 0.5 700 650 1400 700 650 700 600 1200 600 600 550 1000 450 400 ILED 800 350 Switching Frequenc y 300 600 250 200 50 400 350 Switching Frequency 300 300 250 TA = 25C V AUX = VIN = 12V 12 LEDs L = 33µ H RS = 300m Ω 50 200 100 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 ADJ Voltage Figure 4. Boost LED Current, Switching Frequency vs. V ADJ 0 0 1 1.5 2 2.5 ADJ Voltage Figure 3. Buck-Boost LED Current, Switching Frequency vs. V ADJ 0 ILED 400 100 200 8LEDs L = 33µ H G I = 0.23 R S = 300m Ω 450 200 150 V AUX = VIN = 24V 100 0 400 TA = 25 °C 150 500 500 LED Current (mA) 500 Switching Frequency (kHz) 550 LED Current (mA) 300 TA = 25C V AUX = VIN = 12V 2LEDs L = 33µ H RS = 300m Ω 250 0.5 0 450 750 Switching Frequency (kHz) NEW PRODUCT Supply Current (mA) 3 Switching Frequency (kHz) Typical Characteristics 0.5 0 1500 V IN = 24V 1250 TA = 25 °C IPWM = 100Hz LED Current (mA) ILED 1000 750 500 250 0 0 10 20 30 40 50 60 70 80 90 100 PWM Duty Cycle (%) Figure 5. ILED vs. PWM Duty Cycle ZXLD1374 Document number: DS35032 Rev. 2 - 2 Figure 6. ILED vs time - PWM pin transient response 7 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Typical Characteristics 1.252 100% 1.251 Reference Voltage (V) LED Current Dimming Factor 80% 60% 40% 1.2505 1.25 1.2495 1.249 20% 1.2485 0% 0 250 500 750 1000 TADJ Pin Voltage (mV) Figure 7. LED Current vs. TADJ Voltage 1.248 -40 -25 -10 5 20 35 50 65 80 95 110 125 Junction Temperature (°C) Figure 8. VREF vs. Temperature 1250 0.9 100% 0.8 90% TA = 25 °C L = 33µH RS = 150m Ω 80% 0.7 Buc k Mode 2 LED S 70% 0.6 60% 0.5 Duty Power Switch On-Resistance (Ω) NEW PRODUCT 1.2515 0.4 50% 40% 0.3 30% 0.2 20% V IN = 12V ILX = 1.3A 0.1 10% 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 Junction Temperature (°C) Figure 9. RDS(ON) vs. Temperature ZXLD1374 Document number: DS35032 Rev. 2 - 2 8 of 37 www.diodes.com 0% 6 12 18 24 30 36 42 48 54 Input Voltage (V) Figure 10. Duty Cycle vs. Input Voltage 60 March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Typical Characteristics – Buck Mode – RS = 146mΩ – L = 33µH - ILED = 1.5A 1.65 TA = 25°C V AUX = VIN L = 33µH RS = 146m Ω 1.60 NEW PRODUCT LED Current (A) 9 LED s 11 LED s 13 LEDs 15 LEDs 1.55 1.50 1.45 3 LED s 1 LED 5 LED s 7 LED s 1.40 1.35 6 18 30 36 48 42 Input Voltage (V) Figure 11. Load Current vs. Input Voltage and Number of LED 12 24 54 60 1200 TA = 25°C V AUX = VIN L = 33µH R S = 146m Ω Switching Frequency (kHz) 1000 800 600 400 200 3 LED s 0 7 LED s 1 LED 6 5 LED s 12 18 13 LEDs 9 LED s 11 LED s 24 30 36 42 48 Input Voltage (V) Figure 12. Frequency vs. Input Voltage and Number of LED 100% 15 LEDs 54 60 15 LEDs 95% 5 LEDs Efficiency 90% 85% 3 LEDs 7 LEDs 9 LEDs 11 LED s 13 LEDs 80% 1 LED 75% 70% TA = 25°C V AUX = VIN 65% 60% L = 33µH R S = 146m Ω 6 ZXLD1374 Document number: DS35032 Rev. 2 - 2 12 18 24 30 36 42 48 Input Voltage (V) Figure 13. Efficiency vs. Input Voltage and Number of LED 9 of 37 www.diodes.com 54 60 March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Typical Characteristics – Buck Mode – RS = 291mΩ - L = 33µH - ILED = 750mA 0.825 TA = 25°C V AUX = VIN L = 33µH R S = 291m Ω 0.800 NEW PRODUCT LED Current (A) 3 LEDs 7 LEDs 15 LEDs 11 LED s 0.775 9 LEDs 5 LEDs 1 LED 13 LEDs 0.750 0.725 0.700 0.675 6 12 1000 24 30 36 42 48 Input Voltage (V) Figure 14. ILED vs. Input Voltage and Number of LED TA = 25°C 800 54 60 11 LED s V AUX = VIN L = 33µH RS = 291m Ω 900 Frequency (kHz) 18 9 LED s 7 LED s 700 5 LED s 600 500 13 LEDs 3 LED s 15 LEDs 400 300 1 LED 200 100 0 6 18 30 36 48 42 Input Voltage (V) Figure 15. Frequency ZXLD1374 - Buck Mode = L = 47μ H 12 100% 5 LED s 24 7 LED s 9 LED s 11 LED s 13 LEDs 54 60 15 LEDs 95% 3 LED s 90% Efficiency 85% 1 LED 80% 75% 70% TA = 25°C 65% 60% 6 ZXLD1374 Document number: DS35032 Rev. 2 - 2 V AUX = VIN L = 33µH R S = 291m Ω 12 18 30 36 48 42 Input Voltage (V) Figure 16. Efficiency vs. Input Voltage and Number of LED 24 10 of 37 www.diodes.com 54 60 March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Typical Characteristics – Boost mode – RS = 150mΩ - L = 33µH – ILED = 325mA – GIRATIO = 0.21 0.358 TA = 25 °C L = 33µH R S = 150m Ω 0.347 R GI1 = 33kΩ NEW PRODUCT LED Current (A) R GI2 = 120kΩ 0.336 0.325 0.314 6 LED s 8 LED s 0.303 0.292 12 10 LEDs 17 12 LEDs 16 LEDs 14 LEDs 22 27 32 37 Input Voltage (V) Figure 17. ILED vs. Input and Number of LED 42 47 700 TA = 25 °C 650 L = 33µH RS = 150m Ω RGI1 = 33kΩ 600 Frequency (kHz) RGI2 = 120kΩ 550 500 450 400 350 300 12 LEDs 14 LEDs 16 LEDs 6 LED s 250 200 8 LED s 12 17 10 LEDs 32 37 27 Input Voltage (V) Figure 18. Frequency vs. Input Voltage and Number LED 22 47 42 100% 6 LED s 8 LED s 10 LEDs 12 LEDs 14 LEDs 16 LEDs Efficiency 95% 90% 85% 80% TA = 25 °C L = 33µH R S = 150m Ω R GI1 = 33kΩ R GI2 = 120kΩ 75% 12 ZXLD1374 Document number: DS35032 Rev. 2 - 2 17 32 37 27 Input Voltage (V) Figure 19. Efficiency vs. Input Voltage and Number of LED 22 11 of 37 www.diodes.com 42 47 March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Typical Characteristics – Boost mode – RS = 150mΩ - L = 33µH – ILED = 350mA – GIRATIO = 0.23 – with bootstrap 0.385 NEW PRODUCT LED Current (A) 0.368 15 LEDs 13 LEDs 11 LE Ds 0.350 7 LEDs 9 LEDs 5 LEDs T A = 2 5° C L = 3 3µH R S = 1 50m Ω 0.333 R GI1 = 36m Ω R GI2 = 120m Ω 0.315 6.5 8 9.5 12.5 11 14 Input Voltage (V) Figure 20. Load Current vs. Input Voltage and Number of LED 15.5 17 700 Switching Frequency (kHz) 600 15 LEDs 500 13 LEDs 11 LED s 400 9 LEDs 7 LEDs 300 5 LEDs 200 TA = 25 °C 100 0 6.5 L = 33µH RS = 150m Ω RGI1 = 36m Ω RGI2 = 120 m Ω 8 9.5 11 12.5 14 Input Voltage (V) Figure 21. Frequency vs. Input Voltage and Number of LED 15.5 17 100% 7 LED s 5 LED s 95% 90% Efficiency 15 LEDs 85% 13 LEDs 80% 9 LED s 11 LED s TA = 25 °C 75% L = 33µH RS = 150m Ω 70% 6.5 ZXLD1374 Document number: DS35032 Rev. 2 - 2 8 9.5 11 12.5 14 Input Voltage (V) Figure 22. Efficiency vs. Input Voltage and Number of LED 12 of 37 www.diodes.com 15.5 17 March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Typical Characteristics – Buck-boost mode – RS = 150mΩ - L = 33µH – ILED = 350mA – GIRATIO = 0.23 – with bootstrap 0.385 0.375 NEW PRODUCT LED Current (mA) 0.365 8 LED s 7 LED s 6 LED s 0.355 0.345 5 LED s 4 LED s 3 LED s 0.335 TA = 25 °C L = 33µH RS = 150m Ω 0.325 RGI1 = 36 m Ω RGI2 = 120m Ω 0.315 6.5 8.0 9.5 11.0 12.5 14.0 Input Voltage (V) Figure 23. LED Current vs. Input Voltage and Number of LED 15.5 17.0 600 6 LED s 8 LED s 7 LED s Switching Frequency (kHz) 500 400 5 LED s 300 4 LED s 3 LED s 200 TA = 25 °C L = 33µH RS = 150m Ω 100 RGI1 = 36kΩ RGI2 = 120kΩ 0 8.0 11.0 12.5 14.0 15.5 Input Voltage (V) Figure 24. Switching Frequency vs. Input Voltage and Number of LED 6.5 100% 95% 9.5 17.0 TA = 25 °C L = 33µH R S = 150m Ω R GI1 = 36KΩ R GI2 = 120kΩ Efficiency 90% 85% 80% 75% 70% 6.5 ZXLD1374 Document number: DS35032 Rev. 2 - 2 8 LED s 8.0 7 LED s 6 LED s 5 LED s 9.5 4 LED s 11.0 12.5 14.0 Input Voltage (V) Figure 25. Efficiency vs. Input Voltage and Number of LED 13 of 37 www.diodes.com 3 LED s 15.5 17.0 March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information The ZXLD1374 is a high accuracy hysteretic inductive Buck/Boost/Buck-boost converter with an internal NMOS switch designed to be used for current-driving single or multiple series-connected LEDs. The device can be configured to operate in Buck, Boost, or Buck-boost modes by suitable configuration of the external components as shown in the schematics shown in the device operation description. NEW PRODUCT Device Operation a) Buck mode The most simple Buck circuit is shown in Figure 26 LED current control in Buck mode is achieved by sensing the coil current in the sense resistor Rs, connected between the two inputs of a current monitor within the control loop block. An output from the control loop drives the input of a comparator which drives the gate of the internal NMOS switch transistor. When the switch is on, current flows from VIN, via Rs, LED, coil and switch to ground. This current ramps up until an upper threshold value is reached. At this point the switch is turned off and the current flows via Rs, LED, coil and D1 back to VIN. When the coil current has ramped down to a lower threshold value the switch is turned on again and the cycle of events repeats, resulting in continuous oscillation. The average current in the LED and coil is equal to the average of the maximum and minimum threshold currents. The ripple current (hysteresis) is equal to the difference between the thresholds. Figure 26. Buck Configuration The control loop maintains the average LED current at the set level by adjusting the thresholds continuously to force the average current in the coil to the value demanded by the voltage on the ADJ pin. This minimizes variation in output current with changes in operating conditions. The control loop also attempts to minimize changes in switching frequency by varying the level of hysteresis. The hysteresis has a defined minimum (typ 5%) and a maximum (typ 20%), the frequency may deviate from nominal in extreme conditions. Loop compensation is achieved by a single external capacitor C1, connected between SHP and SGND. Figure 27. Operating Waveforms (Buck Mode) ZXLD1374 Document number: DS35032 Rev. 2 - 2 14 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) b) Boost and Buck-boost modes A basic ZXLD1374 application circuit for Buck-boost and Boost modes is shown in Figure 28. NEW PRODUCT Control in Boost and Buck-boost mode is achieved by sensing the coil current in the series resistor Rs, connected between the two inputs of a current monitor within the control loop block. An output from the control loop drives the input of a comparator which drives the gate of the internal NMOS switch transistor. In Boost and Buck-boost modes, when the switch is on, current flows from VIN, via Rs, coil and switch to ground. This current ramps up until an upper threshold value is reached. At this point the switch is turned off and the current flows via Rs, coil, D1 and LED back to VIN (Buck-boost mode), or GND (Boost mode). When the coil current has ramped down to a lower threshold value the switch is turned on again and the cycle of events repeats, resulting in continuous oscillation. The average current in the coil is equal to the average of the maximum and minimum threshold currents and the ripple current (hysteresis) is equal to the difference between the thresholds. Figure 28. Boost and Buck-boost Configuration The average current in the LED is always less than the average current in the coil and the ratio between these currents is set by the values of external resistors RGI1 and RGI2. The peak LED current is equal to the peak coil current. The control loop maintains the average LED current at the set level by adjusting the thresholds and the hysteresis continuously to force the average current in the coil to the value demanded by the voltage on the ADJ and GI pins. This minimizes variation in output current with changes in operating conditions. Loop compensation is achieved by a single external capacitor C2, connected between SHP and SGND. For more detailed descriptions of device operation and for choosing external components, please refer to the application circuits and descriptions in the later sections of this specification. Figure 29. Operating Waveforms (Boost and Buck-boost Modes) ZXLD1374 Document number: DS35032 Rev. 2 - 2 15 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) Component Selection NEW PRODUCT External component selection is driven by the characteristics of the load and the input supply, since this will determine the kind of topology being used for the system. Component selection starts with the current setting procedure and the inductor/frequency setting. Finally after selecting the freewheeling diode and the output capacitor (if needed), the application section will cover the PWM dimming and thermal feedback. Setting the output current The first choice when defining the output current is whether the device is operating with the load in series with the sense resistor (Buck mode) or whether the load is not in series with the sense resistor (Boost and Buck-boost modes). The output current setting depends on the choice of the sense resistor RS, the voltage on the ADJ pin and the voltage on the GI pin, according to the device working mode. The sense resistor RS sets the coil current IRS. The ADJ pin may be connected directly to the internal 1.25V reference (VREF) to define the nominal 100% LED current. The ADJ pin can also be overdriven with an external dc voltage between 125mV and 2.5V to adjust the LED current proportionally between 10% and 200% of the nominal value. ADJ and GI are high impedance inputs within their normal operating voltage ranges. An internal 2.6V clamp protects the device against excessive input voltage and limits the maximum output current to approximately 4% above the maximum current set by VADJ if the maximum input voltage is exceeded. Below are provided the details of the LED current calculation both when the load in series with the sense resistor (Buck mode) and when the load is not in series with the sense resistor (Boost and Buck-boost modes). RS In Buck mode, GI is connected to ADJ which results in the average LED current (ILED) equal to the average sense resistor/coil current (IRS). A loop gain compensation factor, K, compensates for GI being connected to ADJ. This gives the following equation for ILED: ILED = IRs = K VIN ISM REF 225mV VADJ 218mV VADJ where K = 0.97 = RS VREF RS VREF ADJ If ADJ (and GI pin) is directly connected to VREF, this becomes: ILED = IRs = 218mV RS GI Therefore: 218mV ILED In Boost and Buck-boost mode GI is connected to ADJ through a voltage divider. With VADJ equal to VREF, the ratio defined by the resistor divider at the GI pin determines the ratio of average LED current (ILED) to average sense resistor/coil current. Rs = ICOIL ILED 1− D = ⇒ VRS = ICOIL xRS = SGND Figure 30: Buck configuration RS VIN ILED xRS 1− D ISM REF Where ILED = VGI VADJ 0.225 = VADJ VREF R S = R GI1 VADJ 0.225 (R GI1 + R GI2 ) VREF R S ADJ R GI2 GI Therefore: Rs = R GI1 RGI1 225mV VADJ (RGI1 + RGI2 ) ILED VREF SGND Figure 31: Boost and Buck-boost connection ZXLD1374 Document number: DS35032 Rev. 2 - 2 16 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) When the ADJ pin is directly connected to the REF pin, this becomes: R GI1 225mV (R GI1 + R GI2 ) ILED Rs = NEW PRODUCT Note that the average LED current for a Boost or Buck-boost converter is always less than the average sense resistor current. For the ZXLD1374, the recommended potential divider ratio is given by: RGI1 ≤ 0.50 (RGI1 + RGI2 ) 0. 2 ≤ It is possible to use a different combination of GI pin voltages and sense resistor values to set the LED current. In general the design procedure to follow is: - Define input conditions in terms of VIN and IIN - Set output conditions in terms of LED current and the number of LEDs - Define controller topology – Buck, Boost or Buck-boost Calculate the maximum duty-cycle as: Buck mode DMAX = VLEDs VINMIN Boost mode DMAX = VLEDS − VIN MIN VLEDS DMAX = VLEDS VLEDS + VIN MIN Buck-boost mode Set the appropriate GIRATIO according to the circuit duty and the max switch current admissible limitations GIRATIO = - R GI1 VGI = ≤ 1 − DMAX (R GI1 + R GI2 ) VADJ Set RGI1 as: 10kΩ ≤ RGI1 ≤ 200kΩ - Calculate RGI2 as: R GI2 ≈ - DMAX x R GI1 1 − DMAX Calculate the sense resistor as: Rs = R GI1 225mV (R GI1 + R GI2 ) ILED If the potential divider ratio is greater than 0.64, the device detects that Buck-mode operation is desired and the output current will deviate from the desired value. ZXLD1374 Document number: DS35032 Rev. 2 - 2 17 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) For example, as in the typical application circuit, in order to get ILED= 350mA with IRS=1.5A the ratio has to be set as: RGI1 VGI ILED = = ≈ 0.23 (RGI1 + RGI2) VADJ IRS NEW PRODUCT Setting RGI1= 33kΩ it results V R GI2 = RGI1( ADJ − 1) = 110kΩ VGI This will result in: Rs = R GI1 225mV = 150mΩ (RGI1 + R GI2 ) ILED Table 1 shows typical resistor values used to determine GIRATIO with E24 series resistors: Table 1 GIRATIO 0.2 0.25 0.3 0.35 0.4 0.45 0.5 RGI1 30kΩ 33kΩ 39kΩ 30kΩ 100kΩ 51kΩ 30kΩ RGI2 120kΩ 100kΩ 91kΩ 56kΩ 150kΩ 62kΩ 30kΩ The values shown have been chosen so that they do not load REF too much or create offset errors due to the GI pin input current. A ZXLD1374 calculator is available from http://www.diodes.com/destools/calculators.html that will help with component selection. INDUCTOR/FREQUENCY SELECTION Recommended inductor values for the ZXLD1374 are in the range 22µH to 100µH. The chosen coil should have a saturation current higher than the peak sensed current and a continuous current rating above the required mean sensed current by at least 50%. The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the recommended limits over the supply voltage and load current range. The frequency compensation mechanism inside the chip tends to keep the frequency within the range 300kHz ~ 400kHz in most of the operating conditions. Nonetheless, the controller allows for higher frequencies when either the number of LEDs or the input voltage increases. The graphs below can be used to select a recommended inductor to maintain the ZXLD1374 switching frequency within a predetermined range when used in different topologies. ZXLD1374 Document number: DS35032 Rev. 2 - 2 18 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) INDUCTOR/FREQUENCY SELECTION NEW PRODUCT 15 Number of LEDs 13 11 9 L=47µH 7 5 L=33µH 3 L=22µH L=10µH 1 0 10 20 30 40 50 60 Supply Voltage (V) Figure 32. 1.5A Buck mode inductor selection for target frequency of 400 kHz 15 13 Number of LEDs 11 9 L=47µH 7 5 L=33µH L=22µH 3 L=10µH 1 0 10 20 30 40 50 60 Supply Voltage (V) Figure 33. 1.5A Buck mode inductor selection for target frequency > 500kHz ZXLD1374 Document number: DS35032 Rev. 2 - 2 19 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) For example, in a Buck configuration (VIN =24V and 6 LEDs), with a load current of 1.5A; if the target frequency is around 400 kHz, the Ideal inductor size is L= 33µH. The same kind of graphs can be used to select the right inductor for a Buck configuration and a LED current of 750mA, as shown in figures 34 and 35. NEW PRODUCT 15 Numb er of LEDs 13 11 9 7 L=100µH 5 L=68µH L=47µH 3 L=33µH 1 0 10 20 30 40 50 60 Supply Voltage (V) Figure 34. 750mA Buck mode inductor selection for target frequency 400kHz 15 Number of LEDs 13 11 9 L=47µH 7 5 L=33µH L=22µH 3 L=10µH 1 0 10 20 30 Supply Voltage (V) 40 50 60 Figure 35: 750mA Buck mode inductor selection for target frequency > 500kHz ZXLD1374 Document number: DS35032 Rev. 2 - 2 20 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) In the case of the Buck-boost topology, the following graphs guide the designer to select the inductor for a target frequency of 400kHz (figure 36) or higher than 500kHz (figure 37). NEW PRODUCT 15 Number of LEDs 13 11 9 L=47µH 7 5 L=33µH 3 L=22µH 1 0 10 20 30 40 50 60 Supply Voltage (V) Figure 36: 350mA Buck-boost mode inductor selection for target frequency 400kHz 15 Number of LEDs 13 11 L=47µH 9 7 5 L=33µH 3 L=22µH 1 0 10 20 30 40 50 60 Supply Voltage (V) Figure 37: 350mA Buck-boost mode inductor selection for target frequency > 500kHz ZXLD1374 Document number: DS35032 Rev. 2 - 2 21 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) For example, in a Buck-boost configuration (VIN =10-18V and 4 LEDs), with a load current of 350mA; if the target frequency is around 400kHz, the Ideal inductor size is L= 33µH. The same size of inductor can be used if the target frequency is higher than 500kHz driving 6LEDs with a current of 350mA from a VIN =12-24V. L=47µH 15 Number of LEDs 13 11 L=33µH 9 7 L=22µH 5 3 1 0 10 20 30 40 50 60 Supply Voltage (V) Figure 38: 350mA Boost mode inductor selection for target frequency 400kHz L=47µH 15 13 Number of LEDs NEW PRODUCT In the case of the Boost topology, the following graphs guide the designer to select the inductor for a target frequency of 400kHz (figure 38) or higher than 500kHz (figure 39). L=33µH 11 9 7 L=22µH 5 3 1 0 10 20 30 40 50 60 Supply Voltage (V) Figure 39: 350mA Boost mode inductor selection for target frequency > 500kHz ZXLD1374 Document number: DS35032 Rev. 2 - 2 22 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) NEW PRODUCT Suitable coils for use with the ZXLD1374 may be selected from the MSS range manufactured by Coilcraft, or the NPIS range manufactured by NIC components. The following websites may be useful in finding suitable components www.coilcraft.com www.niccomp.com www.wuerth-elektronik.de DIODE SELECTION For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode* with low reverse leakage at the maximum operating voltage and temperature. The Schottky diode also provides better efficiency than silicon PN diodes, due to a combination of lower forward voltage and reduced recovery time. It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than the maximum output load current. In particular, it is recommended to have a voltage rating at least 15% higher than the maximum LX voltage to ensure safe operation during the ringing of the switch node and a current rating at least 10% higher than the average diode current. The power rating is verified by calculating the power loss through the diode. The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on the LX pin. If a silicon diode is used, care should be taken to ensure that the total voltage appearing on the LX pin, including supply ripple, does not exceed the specified maximum value. *A suitable Schottky diode would be PDS3100 (Diodes Inc). OUTPUT CAPACITOR An output capacitor may be required to limit interference or for specific EMC purposes. For Boost and Buck-boost regulators, the output capacitor provides energy to the load when the freewheeling diode is reverse biased during the first switching subinterval. An output capacitor in a Buck topology will simply reduce the LED current ripple below the inductor current ripple. In other words, this capacitor changes the current waveform through the LED(s) from a triangular ramp to a more sinusoidal version without altering the mean current value. In all cases, the output capacitor is chosen to provide a desired current ripple of the LED current (usually recommended to be less than 40% of the average LED current). Buck: C OUTPUT = ΔIL − PP 8 x fSW x rLED x ΔILED − PP Boost and Buck-boost COUTPUT = D x ILED fSW x rLED x ΔILED − PP where: • ΔIL is the ripple of the inductor current, usually ± 20% of the average sensed current • ΔILED is the ripple of the LED current, it should be <40% of the LEDs average current • fsw is the switching frequency (from graphs and calculator) • rLED is the dynamic resistance of the LEDs string (n times the dynamic resistance of the single LED from the datasheet of the LED manufacturer). The output capacitor should be chosen to account for derating due to temperature and operating voltage. It must also have the necessary RMS current rating. The minimum RMS current for the output capacitor is calculated as follows: Buck I ICOUTPUT −RMS = LED − PP 12 ZXLD1374 Document number: DS35032 Rev. 2 - 2 23 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) Boost and Buck-boost ICOUTPUT − RMS = ILED DMAX 1 − DMAX NEW PRODUCT Ceramic capacitors with X7R dielectric are the best choice due to their high ripple current rating, long lifetime, and performance over the voltage and temperature ranges. BOOTSTRAP CIRCUIT In Boost and Buck-boost modes with input voltages below 12V to fully enhance the internal power switch it is required to use a bootstrap network as shown in figure 40. Figure 40: Bootstrap circuit for low voltage operations The bootstrap circuit is realized by adding a reservoir capacitor, C8, current limiting resistor R13 (=100Ω) and a blocking diode D2 (DFSL160). During the power switch turn-on C8 needs to be able to supply approximately 10mA current. A capacitor of 1µF (C8) provides a reasonable trade-off between VAUX supply needs and LED current accuracy. At start-up the VAUX pin requires only a few mA of current from the LED current. In normal operation the current taken from the LED current to supply VAUX will be negligible. INPUT CAPACITOR The input capacitor and minimum RMS current for the output capacitor can be calculated knowing the input voltage ripple ΔVIN-PP as follows: Input capacitor Minimum RMS current Buck CIN = D x(1 − D)x ILED fSW x ΔVIN −PP ICIN − RMS = ILED x Dx(1 − D ) use D=0.5 as worst case use D=0.5 as worst case Boost CIN = ΔICOIL − PP 8 x fSW x ΔVIN − PP I ICIN −RMS = L − PP 12 Buck-boost CIN = D x ILED fSW x ΔVIN −PP ICIN− RMS = ILED x Use D = DMAX as worst case ZXLD1374 Document number: DS35032 Rev. 2 - 2 D (1 − D) Use D = DMAX as worst case 24 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) PWM OUTPUT CURRENT CONTROL & DIMMING The ZXLD1374 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with 1000:1 resolution; however higher dimming frequencies can be used – at the expense of dimming dynamic range and accuracy. 15.0% 1500 Normalized LED current error 12.5% 1250 VIN = 24V TA = 25°C fPWM = 1kHz 10.0% 1000 7.5% 750 ILED 5.0% 500 2.5% 250 Normalized LED Current Error 0.0% 0% 10% 20% 30% 40% 50% 60% LED current (mA) NEW PRODUCT Typically, for a PWM frequency of 1kHz, the error on the current linearity is lower than 5%; in particular the accuracy is better than 1% for PWM from 5% to 100%. This is shown in the graph below: 70% 80% 90% 0 100% PWM duty cycle Figure 41. LED current linearity and accuracy with PWM dimming at 1kHz 15.0% 1500 12.5% 1250 VIN = 24V TA = 25°C fPWM = 100Hz 10.0% 1000 ILED 7.5% 750 5.0% 500 2.5% LED current (mA) Normalized LED current error For a PWM frequency of 100Hz, the error on the current linearity is lower than 2.5%; it becomes negligible for PWM greater than 5%. This is shown in the graph below: 250 Normalized LED Current Error 0.0% 0% 10% 20% 30% 40% 50% 60% PWM duty cycle 70% 80% 90% 0 100% Figure 42. LED current linearity and accuracy with PWM dimming at 100Hz ZXLD1374 Document number: DS35032 Rev. 2 - 2 25 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) NEW PRODUCT The PWM pin is designed to be driven by both 3.3V and 5V logic levels. It can be driven also by an open drain/collector transistor. In this case the designer can either use the internal pull-up network or an external pull-up network in order to speed-up PWM transitions, as shown in the Boost/ Buck-boost section. Figure 43. PWM Dimming from Open Collector Switch Figure 44. PWM Dimming from MCU LED current can be adjusted digitally, by applying a low frequency PWM logic signal to the PWM pin to turn the controller on and off. This will produce an average output current proportional to the duty cycle of the control signal. During PWM operation, the device remains powered up and only the output switch is gated by the control signal. The PWM signal can achieve very high LED current resolution. In fact, dimming down from 100% to 0, a minimum pulse width of 5us can be achieved resulting in very high accuracy. While the maximum recommended pulse is for the PWM signal is10ms. Figure 45. PWM Dimming Minimum and Maximum Pulse ZXLD1374 Document number: DS35032 Rev. 2 - 2 26 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) NEW PRODUCT The device can be put in standby by taking the PWM pin to ground, or pulling it to a voltage below 0.4V with a suitable open collector NPN or open drain NMOS transistor, for a time exceeding 15ms (nominal). In the shutdown state, most of the circuitry inside the device is switched off and residual quiescent current will be typically 90µA. In particular, the Status pin will go down to GND while the FLAG and REF pins will stay at their nominal values. Fig 46. Stand-by state from PWM signal TADJ pin - Thermal control of LED current The ‘Thermal control’ circuit monitors the voltage on the TADJ pin and reduces output current if the voltage on this pin falls below 625mV. An external NTC thermistor and resistor can therefore be connected as shown below to set the voltage on the TADJ pin to 625mV at the required temperature threshold. This will give 100% LED current below the threshold temperature and a falling current above it as shown in the graph. The temperature threshold can be altered by adjusting the value of Rth and/or the thermistor to suit the requirements of the chosen LED. The Thermal Control feature can be disabled by connecting TADJ to REF. Here is a simple procedure to design the thermal feedback circuit: 1. Select the temperature threshold TTHRESHOLD at which the current must start to decrease 2. Select the Thermistor TH1 (both resistive value at 25˚C and beta) 3. Select the value of the resistor RTH as RTH = TH1 at TTHRESHOLD Figure 47. Thermal feedback network For example, 1) Temperature threshold TTHRESHOLD = 70˚C 2) TH1 = 10kΩ at 25˚C and beta= 3500 3) RTH = TH1 at TTHRESHOLD = 3.3kΩ ZXLD1374 Document number: DS35032 Rev. 2 - 2 Æ TH1 = 3.3kΩ at 70˚C 27 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) Over-Temperature Shutdown NEW PRODUCT The ZXLD1374 incorporates an over-temperature shutdown circuit to protect against damage caused by excessive die temperature. A warning signal is generated on the STATUS output when die temperature exceeds 125°C nominal and the output is disabled when die temperature exceeds 150°C nominal. Normal operation resumes when the device cools back down to 125°C. FLAG/STATUS Outputs The FLAG/STATUS outputs provide a warning of extreme operating or fault conditions. FLAG is an open-drain logic output, which is normally high resistance, but switches low resistance to indicate that a warning, or fault condition exists. STATUS is a DAC output, which is normally high (4.5V), but switches to a lower voltage to indicate the nature of the warning/fault. Conditions monitored, the method of detection and the nominal STATUS output voltage are given in the following table: Table 2 Warning/Fault condition Severity (Note 13) Monitored parameters Normal operation FLAG Nominal STATUS voltage H 4.5 1 VAUX<5.6V L 4.5 2 VIN<5.6V L 3.6 Output current out of regulation (Note 14) 2 VSHP outside normal voltage range L 3.6 Driver stalled with switch ‘on’, or ‘off’ (Note 15) 2 tON, or tOFF>100µs L 3.6 Switch over-voltage 3 LX voltage > 60V L 2.7 Device temperature above maximum recommended operating value 4 TJ>125°C L 1.8 Sense resistor current IRS above specified maximum 5 VSENSE>0.375V L 0.9 Average switch current greater than 1.5A 5 ILX > 1.5A L 0.9 Supply under-voltage Notes: 13. Severity 1 denotes lowest severity. 14. This warning will be indicated if the output power demand is higher than the available input power; the loop may not be able to maintain regulation. 15. This warning will be indicated if the LX pin stays at the same level for greater than 100us (e.g. the internal transistor cannot pass enough current to reach the upper switching threshold). ZXLD1374 Document number: DS35032 Rev. 2 - 2 28 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 NEW PRODUCT FLAG VOLTAGE Applications Information (Continued) VR EF 0V 4.5V Normal Operations VAUX UVLO STAT US VOLTA GE 3.6V - VI N UVLO - STALL - OU T of REG 2.7V ZXLD1374 Switch OV 1.8V Over Temperature 0.9V Over C urrent 0A 0 1 2 3 5 4 SEVERITY Fig 48. Status levels In the event of more than one fault/warning condition occurring, the higher severity condition will take precedence. E.g. ‘Excessive coil current’ and ‘Out of regulation’ occurring together will produce an output of 0.9V on the STATUS pin. If VADJ>1.7V, VSENSE may be greater than the excess coil current threshold in normal operation and an error will be reported. Hence, STATUS and FLAG are only guaranteed for VADJ<=VREF. Diagnostic signals should be ignored during the device start – up for 100μs. The device start up sequence will be initiated both during the first power on of the device or after the PWM signal is kept low for more than 15ms, initiating the standby state of the device. In particular, during the first 100μs the diagnostic is signaling an over-current then an out-of-regulation status. These two events are due to the charging of the inductor and are not true fault conditions. FLAG VREF Coil current (A) STATUS Out of regulation Overcurrent 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 20 40 60 80 100 time (µs) 120 140 160 180 200 Figure 49. Diagnostic during Start-Up ZXLD1374 Document number: DS35032 Rev. 2 - 2 29 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) Over-voltage Protection NEW PRODUCT The ZXLD1374 is inherently protected against open-circuit load when used in Buck configuration. However care has to be taken with open-circuit load conditions in Buck-boost or Boost configurations. This is because in these configurations there is only an over-voltage FLAG but no internal open-circuit protection mechanism for the internal MOSFET. In this case an Over-Voltage-Protection (OVP) network should be provided to the MOSFET to avoid damage due to open circuit conditions. This is shown in Figure 37 below, highlighted in the dotted blue box. Figure 50. OVP Circuit The zener voltage is determined according to: VZ = VLEDMAX +10%. If the LX pin voltage exceeds VZ the gate of MOSFET Q1 will rise turning Q1 on. This will pull the PWM pin low and disable the LX output until the voltage on the LX falls below Vz. If the LX pin remains above VZ for longer than 20ms then the ZXLD1374 will enter into a shutdown state. Care should be taken such that the maximum gate voltage of the Q1 MOSFET is not exceeded. An alternative,solution for OVP function is to use the diagnostic section of the ZXLD1374 to initiate the disabling of the LX pin. For example, a microcontroller could be used to respond to the FLAG and the status pins, and if an over-voltage state is indicated, the microcontroller could switch the device off by pulling the PWM signal low. ZXLD1374 Document number: DS35032 Rev. 2 - 2 30 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Information (Continued) PCB Layout considerations NEW PRODUCT PCB layout is a fundamental activity to get the most of the device in all configurations. In the following section it is possible to find some important insight to design with the ZXLD1374 both in Buck and Buck-boost/Boost configurations. Figure 51. Circuit Layout Here are some considerations useful for the PCB layout: In order to avoid ringing due to stray inductances, the inductor L1, the anode of D1 and the LX pin should be placed as close together as possible. The shaping capacitor C1 is fundamental for the stability of the control loop. To this end it should be placed no more than 5mm from the SHP pin. Input voltage pins, VIN and VAUX, need to be decoupled. It is recommended to use two ceramic capacitors of 2.2µF, X7R, 100V (C3 and C4). In addition to these capacitors, it is suggested to add two ceramic capacitors of 1uF, X7R, 100V each (C2, C8), as well as a further decoupling capacitor of 100nF close to the VIN/VAUX pins (C9) the device is used in Buck mode, or can be driven from a separate supply. ZXLD1374 Document number: DS35032 Rev. 2 - 2 31 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Examples In this application example, ZXLD1374 is connected as a Buck LED driver with schematic and parts list shown below. The LED driver is able to deliver 1.5A of LED current to single or multiple LEDs in series with input voltage ranged from 10V to 50V. In order to achieve high efficiency under high LED current, Super Barrier Rectifier (SBR) with low forward voltage is used as free wheeling rectifier. With only a few extra components, the ZXLD1374 LED driver is able to deliver LED power of greater than 60W. This is suitable for applications which require high LED power likes high power down lighting, wall washer, automotive LED lighting etc. Figure 52. Application circuit of 1.5A Buck LED driver Bill of Material Ref No. U1 D1 L1 C1 C2 C3 C4 C5 R1 R2 R3 Value Part No. Manufacturer 60V 1.5A LED driver 100V 3A SBR 33µH 4.2A 100pF 50V 1µF 100V X7R 2.2µF 100V X7R 300mΩ 1% 4.7Ω ZXLD1374 SBR3U100 744770933 SMD 0805/0603 SMD1206 SMD1210 SMD1206 SMD1206 Diodes Inc Diodes Inc Wurth Electronik Generic Generic Generic Generic Generic Typical Performance LED Current vs Input Voltage Efficiency vs Input Voltage 100% 1600 90% LED Current (mA) 80% Efficiency (%) NEW PRODUCT 1.5A Buck LED driver 70% 60% 50% 40% 1 LED VF=3.4V 3 LED VF=9.8V 5 LED VF=16V 30% 20% 1200 800 1 LED VF=3.4V 3 LED VF=9.8V 5 LED VF=16V 400 10% 0% 10 15 20 25 30 35 40 45 50 Input Voltage (V) Document number: DS35032 Rev. 2 - 2 10 15 20 25 30 35 40 45 50 Input Voltage (V) Figure 53. Efficiency ZXLD1374 0 Figure 54. Line regulation 32 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Applications Examples In this application example, ZXLD1374 is connected as a Boost LED driver with schematic and parts list shown below. The LED driver is able to deliver 350mA of LED current into 12 high brightness LED with input voltage ranged from 16V to 28V. Overall high efficiency of 92%+ make it ideal for applications likes solar LED street lighting and general LED illuminations. Figure 55. Application circuit of 350mA Boost LED driver Bill of Material Ref No. U1 Q1 D1 Z1 L1 C1 C3 C4 C2 R1 R2 R3 R4 R5 Value 60V LED driver 60V MOSFET 100V 3A Schottky 51V 410mW Zener 47µH 2.6A 100pF 50V 4.7µF 100V X7R 1µF 50V X7R 300mΩ 1% 120kΩ 1% 36kΩ 1% 2.7kΩ Part No. ZXLD1374 2N7002A PDS3100-13 BZT52C51 744771147 SMD 0805/0603 SMD1210 SMD1206 SMD1206 SMD 0805/0603 SMD 0805/0603 SMD 0805/0603 Manufacturer Diodes Inc Diodes Inc Diodes Inc Diodes Inc Wurth Electronik Generic Generic Generic Generic Generic Generic Typical Performance Efficiency vs Input Voltage LED Current vs Input Voltage 100% 400 90% 350 80% 300 LED Current 70% Efficiency NEW PRODUCT 350mA Boost LED diver 60% 50% 40% 30% 12 LED VF=37V 15 LED VF=47V 20% 250 200 150 100 12 LED VF=37V 15 LED VF=47V 50 10% 0 0% 16 18 20 22 24 26 28 30 Document number: DS35032 Rev. 2 - 2 18 20 22 24 26 28 30 Figure 57. Line regulation Figure 56. Efficiency ZXLD1374 16 Input Voltage Input Voltage 33 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 350mA Buck-boost LED driver In this application example, ZXLD1374 is connected as a Buckboost LED driver with schematic and parts list shown below. The LED driver is able to deliver 350mA of LED current into 4/5 high brightness LED with input voltage ranged from 7V to 20V. In order to increase the driving voltage level for the internal MOSFET during low voltage input, bootstrap circuit formed by R6 D2 and C6 are used to supply higher voltage to the VAUX pin. Since the Buck-boost LED driver can handle an input voltage range below and above the LED voltage, this versatile input voltage range makes it ideal for automotive lighting applications. Figure 58. Application circuit of 350mA Buck-boost LED driver Bill of Material Ref No. U1 Q1 D1 D2 Z1 L1 C1 C3 C4 C5 C2 C6 R1 R2 R3 R4 R5 R6 Value 60V LED driver 60V MOSFET 100V 3A Schottky 100V 1A Schottky 47V 410mW Zener 47µH 2.6A 100pF 50V 4.7µF 50V X7R 1µF 50V X7R 300mΩ 1% 120kΩ 1% 36kΩ 1% 2.7kΩ 1kΩ Part No. ZXLD1374 2N7002A PDS3100-13 B1100 BZT52C47 744771147 SMD 0805/0603 SMD1210 SMD1206 SMD1206 SMD 0805/0603 SMD 0805/0603 SMD 0805/0603 SMD 1206 Manufacturer Diodes Inc Diodes Inc Diodes Inc Diodes Inc Diodes Inc Wurth Electronik Generic Generic Generic Generic Generic Generic Generic Generic Typical Performance LED Current vs Input Voltage Efficiency vs Input Voltage 100% 90% 400 80% 350 70% 300 LED Current Efficiency NEW PRODUCT Applications Examples 60% 50% 40% 30% 250 200 150 100 20% 4 LED VF=12.5V 5 LED VF=15.6V 10% 4 LED VF=12.5V 5 LED VF=15.6V 50 0 0% 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Document number: DS35032 Rev. 2 - 2 8 9 10 11 12 13 14 15 16 17 18 19 20 Figure 60. Line Regulation Figure 59. Efficiency ZXLD1374 7 Input Voltage Input Voltage 34 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Thermal Impedance 4 3.5 Power dissipation (mW) NEW PRODUCT 3 2.5 2 1.5 1 0.5 0 -40 -25 -10 5 20 35 50 65 80 95 110 Ambient temperature (°C) Figure 61. Power Derating Curve ZXLD1374 Document number: DS35032 Rev. 2 - 2 35 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 Ordering Information Device Packaging Status ZXLD1374EST20TC TSSOP-20EP Active Part Marking ZXLD 1374 YYWW Reel Quantity Tape Width Reel Size 2500 16mm 13” NEW PRODUCT Where YY stands for last 2 digits of year - 10, 11 and WW stands for week number Package Mechanical Data TSSOP-20EP θ1 ZXLD1374 Document number: DS35032 Rev. 2 - 2 36 of 37 www.diodes.com March 2011 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1374 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER WITH AEC-Q100 IMPORTANT NOTICE NEW PRODUCT DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION). 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