A Product Line of Diodes Incorporated ZXLD1366 HIGH ACCURACY 1A, 60V LED DRIVER WITH INTERNAL SWITCH Description Pin Assignments (TOP VIEW) The ZXLD1366 is a continuous mode inductive step-down converter, designed for driving single or multiple series connected LEDs efficiently from a voltage source higher than the LED voltage. The device operates from an input supply between 6V and 60V and provides an externally adjustable output current of up to 1A. Depending upon supply voltage and external components, this can provide up to 48 watts of output power. LX 1 GND 2 TSOT23-5 (TOP VIEW) The ADJ pin will accept either a DC voltage or a PWM waveform. Depending upon the control frequency, this will provide either a continuous (dimmed) or a gated output current. Soft-start can be forced using an external capacitor from the ADJ pin to ground. GND 2 5 GND ADJ 3 4 ISENSE DFN3030-6 (TOP VIEW) Applying a voltage of 0.2V or lower to the ADJ pin turns the output off and switches the device into a low current standby state. LX 1 Features • • • • 6 VIN LX 1 Output current can be adjusted above, or below the set value, by applying an external control signal to the 'ADJ' pin. Typically better than 0.8% output current accuracy Available in thermally enhanced DFN package Simple and with low part count Single pin on/off and brightness control using DC voltage or PWM PWM resolution up to 1000:1 High efficiency (up to 97%) Wide input voltage range: 6V to 60V Inherent open-circuit LED protection 4 ISENSE ADJ 3 The ZXLD1366 includes the output switch and a high-side output current sensing circuit, which uses an external resistor to set the nominal average output current. • • • • 5 VIN 8 VIN GND 2 GND 3 6 GND ADJ 4 5 ISENSE 7 GND SO-8-EP Typical Application Circuit D1 Rs VIN (24V) 0.2V Applications • • • • • • • • • Low voltage halogen replacement LEDs Automotive lighting Low voltage industrial lighting LED back-up lighting Illuminated signs Emergency lighting SELV lighting LCD TV backlighting Refrigeration lights L1 C1 4.7mF 100nF VIN ISENSE ADJ ZXLD1366 LX GND GND . ZXLD1366 Document number: DS31992 Rev. 5 - 2 1 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Block Diagram D1 VIN L1 RS 5 5V C1 4.7mF 4 VIN ISENSE 1 LX R1 Voltage regulator + 0.2V + Low voltage detector MN + Adj 3 R5 20K R4 50K D1 1.25V 600KHz R2 + R3 1.35V Gnd 2 Figure 1 Pin connection for TSOT23-5 package Pin Description Name TSOT23-5 DFN3030-6 SO8-EP Description LX GND 1 2 1 2, 5 1 2, 3, 6, 7 ADJ 3 3 4 ISENSE 4 4 5 VIN 5 6 8 Drain of NDMOS switch Ground (0V) Multi-function On/Off and brightness control pin: • Leave floating for normal operation.(VADJ = VREF = 1.25V giving nominal average output current IOUTnom = 0.2V/RS) • Drive to voltage below 0.2V to turn off output current • Drive with DC voltage (0.3V < VADJ < 2.5V) to adjust output current from 25% to 200% of IOUTnom • Connect a capacitor from this pin to ground to set soft-start time. Soft start time increases approximately 0.2ms/nF Connect resistor RS from this pin to VIN to define nominal average output current IOUTnom = 0.2V/RS (Note: RSMIN = 0.2V with ADJ pin open-circuit) Input voltage (6V to 60V). Decouple to ground with 4.7µF of higher X7R ceramic capacitor close to device ZXLD1366 Document number: DS31992 Rev. 5 - 2 2 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated) Symbol Parameter VIN Input Voltage VSENSE ISENSE Voltage +0.3 to -5 VADJ ILX Adjust Pin Input Voltage Switch Output Current Power Dissipation TJ MAX V V (measured with respect to VIN) LX Output Voltage TOP TST Unit (65V for 0.5 sec) VLX PTOT Rating -0.3 to +60 -0.3 to +60 V (65V for 0.5 sec) (Refer to Package thermal de-rating curve on page 26) Operating Temperature Storage Temperature Junction Temperature -0.3 to +6 1.25 SOT23-5; 1 DFN; 1.8 -40 to 125 -55 to 150 150 V A W °C °C °C These are stress ratings only. Operation above the absolute maximum rating may cause device failure. Operation at the absolute maximum ratings, for extended periods, may reduce device reliability. Thermal Resistance Parameter θJA Junction to Ambient TSOT23-5 82 ΨJB Junction to Board 33 - - θJC Junction to Case - 7 14 Electrical Characteristics Parameter Input voltage Internal regulator start-up threshold Internal regulator shutdown threshold Quiescent supply current with output off IINQon Quiescent supply current with output switching(C) VSENSE Mean current sense threshold voltage (Defines LED current setting accuracy) VSENSEHYS ISENSE Sense threshold hysteresis VREF Internal reference voltage DVREF/DT Temperature coefficient of VREF VADJoff °C/W (a) ISENSE pin input current Condition (b) See note Min. 6 4.4 ADJ pin grounded ADJ pin floating, L=68mH, 3 LEDs, f=260kHz Measured on ISENSE pin with respect to VIN VADJ=1.25V; VIN=18V Typ. 4.85 4.75 65 Max. 60 5.2 108 1.6 195 200 ±15 4 VSENSE = VIN -0.2 Measured on ADJ pin with pin floating External control voltage range on ADJ pin (d) for DC brightness control DC voltage on ADJ pin to switch device from VADJ falling active (on) state to quiescent (off) state VADJ Unit DFN3030-6 44 (Test conditions: VIN = 24V, Tamb = 25°C, unless otherwise specified.) Symbol VIN VSU VSD IINQoff Notes: Rating SO-8-EP 45 Symbol V V µA mA 205 mV 10 % µA 1.25 V 50 ppm/° C 0.3 0.15 Unit 0.2 2.5 V 0.27 V (a) Production testing of the device is performed at 25°C. Functional operation of the device and parameters specified over a -40°C to +105°C temperature range, are guaranteed by design, characterization and process control. (b) VIN > 16V to fully enhance output transistor. Otherwise out current must be derated - see graphs. Operation at low supply may cause excessive heating due to increased on-resistance. Tested at 7V guaranteed for 6V by design. (c) Static current of device is approximately 700 mA, see Graph, Page 17 (d) 100% brightness corresponds to VADJ = VADJ(nom) = VREF. Driving the ADJ pin above VREF will increase the VSENSE. Threshold and output current proportionally ZXLD1366 Document number: DS31992 Rev. 5 - 2 3 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Electrical Characteristics Symbol VADJon (a) (Test conditions: VIN = 24V, Tamb = 25°C, unless otherwise specified.) Parameter DC voltage on ADJ pin to switch device from quiescent (off) state to active (on) state Condition RADJ Resistance between ADJ pin and VREF ILXmean RLX ILX(leak) Continuous LX switch current LX switch ‘On’ resistance LX switch leakage current Duty cycle range of PWM signal applied to ADJ pin during low frequency PWM dimming mode Brightness control range DC Brightness control range DPWM(LF) DCADJ(*) Soft start time TSS Operating frequency (See graphs for more details) fLX TONmin TOFFmin TPWmin_REC fLXmax DLX Notes: Minimum switch ‘ON’ time Minimum switch ‘OFF’ time Recommended minimum switch pulse width Recommended maximum operating frequency Recommended duty cycle range of output switch at fLXmax (cont.) Min. Typ. Max. Unit VADJ rising 0.2 0.25 0.3 V 0< VADJ< VREF VADJ>VREF +100mV 30 10.4 50 14.2 65 18 kΩ 0.5 1 0.75 5 A Ω µA @ ILX = 1A PWM frequency <300Hz PWM amplitude = VREF Measured on ADJ pin 0.001 1 1000:1 5:1 (*) See note Time taken for output current to reach 90% of final value after voltage on ADJ pin has risen above 0.3V. Requires external capacitor 22nF. See graphs for more details ADJ pin floating L=68mH (0.2V) IOUT=1A @ VLED=3.6V Driving 3 LEDs LX switch ‘ON’ LX switch ‘OFF’ 2 ms 260 kHz (†) LX switch ‘ON’ or ‘OFF’ 130 (†) 70 ns ns 800 ns 500 0.3 kHz 0.7 (*) Ratio of maximum brightness to minimum brightness before shutdown VREF = 1.25/0.3. VREF externally driven to 2.5V, ratio 10:1. (†) Parameters are not tested at production. Parameters are guaranteed by design, characterization and process control. ZXLD1366 Document number: DS31992 Rev. 5 - 2 4 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Device Description The device, in conjunction with the coil (L1) and current sense resistor (RS), forms a self-oscillating continuous-mode buck converter. Device operation (refer to Figure 1 - Block diagram and Figure 2 Operating waveforms) Operation can be best understood by assuming that the ADJ pin of the device is unconnected and the voltage on this pin (VADJ) appears directly at the (+) input of the comparator. When input voltage VIN is first applied, the initial current in L1 and RS is zero and there is no output from the current sense circuit. Under this condition, the (-) input to the comparator is at ground and its output is high. This turns MN on and switches the LX pin low, causing current to flow from VIN to ground, via RS, L1 and the LED(s). The current rises at a rate determined by VIN and L1 to produce a voltage ramp (VSENSE) across RS. The supply referred voltage VSENSE is forced across internal resistor R1 by the current sense circuit and produces a proportional current in internal resistors R2 and R3. This produces a ground referred rising voltage at the (-) input of the comparator. When this reaches the threshold voltage (VADJ), the comparator output switches low and MN turns off. The comparator output also drives another NMOS switch, which bypasses internal resistor R3 to provide a controlled amount of hysteresis. The hysteresis is set by R3 to be nominally 15% of VADJ. When MN is off, the current in L1 continues to flow via D1 and the LED(s) back to VIN. The current decays at a rate determined by the LED(s) and diode forward voltages to produce a falling voltage at the input of the comparator. When this voltage returns to VADJ, the comparator output switches high again. This cycle of events repeats, with the comparator input ramping between limits of VADJ ± 15%. Switching thresholds With VADJ = VREF, the ratios of R1, R2 and R3 define an average VSENSE switching threshold of 200mV (measured on the ISENSE pin with respect to VIN). The average output current IOUTnom is then defined by this voltage and RS according to: IOUTnom = 200mV/RS Nominal ripple current is ±30mV/RS Adjusting output current The device contains a low pass filter between the ADJ pin and the threshold comparator and an internal current limiting resistor (50kΩ nom) between ADJ and the internal reference voltage. This allows the ADJ pin to be overdriven with either DC or pulse signals to change the VSENSE switching threshold and adjust the output current. Details of the different modes of adjusting output current are given in the applications section. Output shutdown The output of the low pass filter drives the shutdown circuit. When the input voltage to this circuit falls below the threshold (0.2V nom.), the internal regulator and the output switch are turned off. The voltage reference remains powered during shutdown to provide the bias current for the shutdown circuit. Quiescent supply current during shutdown is nominally 60μA and switch leakage is below 5μA. ZXLD1366 Document number: DS31992 Rev. 5 - 2 5 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 VIN LX voltage 0V Toff Ton VIN 230mV 170mV SENSE voltage 200mV VSENSEVSENSE+ IOUTnom +15% IOUTnom Coil current IOUTnom -15% 0V Comparator input voltage 0.15VADJ VADJ 0.15VADJ Comparator output 5V 0V Figure 2 Theoretical Operating Waveforms ZXLD1366 Document number: DS31992 Rev. 5 - 2 6 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Actual operating waveforms [VIN=15V, RS=0.2V, L=68µH] Normal operation. Output current (Ch3) and LX voltage (Ch2) Actual operating waveforms [VIN=30V, RS=0.2V, L=68µH] Normal operation. Output current (Ch3) and LX voltage (Ch2) Actual operating waveforms [VIN=60V, RS=0.2V, L=68µH] Normal operation. Output current (Ch3) and LX voltage (Ch2) ZXLD1366 Document number: DS31992 Rev. 5 - 2 7 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Typical Operating Conditions ZXLD1366 Output Current L=68µH 1.100 01 LEDs 03 LEDs 1.080 05 LEDs 07 LEDs 09 LEDs 11 LEDs Output Current (A) 1.060 13 LEDs 15 LEDs 1.040 1.020 1.000 0.980 0 10 20 30 40 50 60 40 50 60 40 50 60 Supply Voltage (V) ZXLD1366 Output Current Deviation L=68µH 10% 8% Output Current Deviation (%) 6% 4% 2% 0% 01 LEDs -2% 03 LEDs 05 LEDs -4% 07 LEDs 09 LEDs -6% 11 LEDs 13 LEDs -8% 15 LEDs -10% 0 10 20 30 Supply Voltage (V) ZXLD1366 Efficiency L=68µH 100% 01 LEDs 03 LEDs 95% 05 LEDs 90% 07 LEDs 09 LEDs Efficiency (%) 85% 11 LEDs 13 LEDs 80% 15 LEDs 75% 70% 65% 60% 55% 50% 0 10 20 30 Supply Voltage (V) ZXLD1366 Document number: DS31992 Rev. 5 - 2 8 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Typical Operating Conditions (cont.) ZXLD1366 Switching Frequency L=68µH 500 450 01 LEDs 03 LEDs 05 LEDs 07 LEDs 09 LEDs 11 LEDs 13 LEDs 15 LEDs Switching Frequency (kHz) 400 350 300 250 200 150 100 50 0 0 10 20 30 40 50 40 50 60 Supply Voltage (V) ZXLD1366 Duty Cycle L=68µH 100% 90% 80% Duty Cycle (%) 70% 60% 50% 01 LEDs 03 LEDs 05 LEDs 07 LEDs 09 LEDs 11 LEDs 13 LEDs 15 LEDs 40% 30% 20% 10% 0% 0 10 20 30 60 Supply Voltage (V) ZXLD1366 Document number: DS31992 Rev. 5 - 2 9 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Typical Operating Conditions (cont.) ZXLD1366 Output Current L=100µH 1.100 01 LEDs 03 LEDs 1.080 05 LEDs 07 LEDs 09 LEDs 11 LEDs Output Current (A) 1.060 13 LEDs 15 LEDs 1.040 1.020 1.000 0.980 0.960 0 10 20 30 40 50 60 Supply Voltage (V) ZXLD1366 Output Current Deviation L=100µH 10% 8% Output Current Deviation (%) 6% 4% 2% 0% 01 LEDs -2% 03 LEDs 05 LEDs -4% 07 LEDs 09 LEDs -6% 11 LEDs 13 LEDs -8% 15 LEDs -10% 0 10 20 30 40 50 60 Supply Voltage (V) ZXLD1366 Efficiency L=100µH 100% 01 LEDs 03 LEDs 05 LEDs 07 LEDs 09 LEDs 11 LEDs 13 LEDs 15 LEDs 95% 90% Efficiency (%) 85% 80% 75% 70% 65% 60% 55% 50% 0 10 20 30 40 50 60 Supply Voltage (V) ZXLD1366 Document number: DS31992 Rev. 5 - 2 10 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Typical Operating Conditions (cont.) ZXLD1366 Switching Frequency L=100µH 500 450 01 LEDs 03 LEDs 05 LEDs 07 LEDs 09 LEDs 11 LEDs 13 LEDs 15 LEDs Switching Frequency (kHz) 400 350 300 250 200 150 100 50 0 0 10 20 30 40 50 60 Supply Voltage (V) ZXLD1366 Duty Cycle L=100µH 100% 90% 80% Duty Cycle (%) 70% 60% 50% 01 LEDs 40% 03 LEDs 05 LEDs 30% 07 LEDs 09 LEDs 11 LEDs 20% 13 LEDs 10% 15 LEDs 0% 0 10 20 30 40 50 60 Supply Voltage (V) ZXLD1366 Document number: DS31992 Rev. 5 - 2 11 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Typical Operating Conditions (cont.) ZXLD1366 Output Current L=150µH 1.100 01 LEDs 03 LEDs 1.080 05 LEDs 07 LEDs Output Current (A) 09 LEDs 1.060 11 LEDs 13 LEDs 15 LEDs 1.040 1.020 1.000 0.980 0 10 20 30 40 50 60 50 60 Supply Voltage (V) ZXLD1366 Output Current Dev iation L=150µH 10% 8% Output Current Deviation (%) 6% 4% 2% 0% 01 LEDs -2% 03 LEDs 05 LEDs -4% 07 LEDs 09 LEDs -6% 11 LEDs 13 LEDs -8% 15 LEDs -10% 0 10 20 30 40 Supply Voltage (V) ZXLD1366 Efficiency L=150µH 100% 01 LEDs 95% 03 LEDs 05 LEDs 90% 07 LEDs 09 LEDs Efficiency (%) 85% 11 LEDs 13 LEDs 80% 15 LEDs 75% 70% 65% 60% 55% 50% 0 10 20 30 40 50 60 Supply Voltage (V) ZXLD1366 Document number: DS31992 Rev. 5 - 2 12 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Typical Operating Conditions (cont.) ZXLD1366 Switching Frequency L=150µH 500 450 01 LEDs 03 LEDs 05 LEDs 07 LEDs 09 LEDs 11 LEDs 13 LEDs 15 LEDs Switching Frequency (kHz) 400 350 300 250 200 150 100 50 0 0 10 20 30 40 50 40 50 60 Supply Voltage (V) ZXLD1366 Duty Cycle L=150µH 100% 90% 80% Duty Cycle (%) 70% 60% 50% 01 LEDs 40% 03 LEDs 05 LEDs 30% 07 LEDs 09 LEDs 20% 11 LEDs 13 LEDs 10% 15 LEDs 0% 0 10 20 30 60 Supply Voltage (V) ZXLD1366 Document number: DS31992 Rev. 5 - 2 13 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Typical Operating Conditions (cont.) ZXLD1366 Output Current L=220µH 1.100 01 LEDs 1.080 03 LEDs 05 LEDs Output Current (A) 07 LEDs 09 LEDs 1.060 11 LEDs 13 LEDs 15 LEDs 1.040 1.020 1.000 0.980 0 10 20 30 40 50 60 Supply Voltage (V) ZXLD1366 Output Current Deviation L=220µH 10% 8% Output Current Deviation (%) 6% 4% 2% 0% 01 LEDs -2% 03 LEDs 05 LEDs -4% 07 LEDs 09 LEDs -6% 11 LEDs 13 LEDs -8% 15 LEDs -10% 0 10 20 30 40 50 60 40 50 60 Supply Voltage (V) ZXLD1366 Efficiency L=220µH Efficiency (%) 100% 95% 01 LEDs 90% 03 LEDs 05 LEDs 07 LEDs 85% 09 LEDs 11 LEDs 80% 13 LEDs 15 LEDs 75% 70% 65% 60% 55% 50% 0 10 20 30 Supply Voltage (V) ZXLD1366 Document number: DS31992 Rev. 5 - 2 14 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Typical Operating Conditions (cont.) ZXLD1366 Switching Frequency L=220µH 500 450 01 LEDs 03 LEDs 05 LEDs 07 LEDs 09 LEDs 11 LEDs 13 LEDs 15 LEDs Switching Frequency (kHz) 400 350 300 250 200 150 100 50 0 0 10 20 30 40 50 60 40 50 60 Supply Voltage (V) ZXLD1366 Duty Cycle L=220µH 100% 90% 80% Duty Cycle (%) 70% 60% 50% 40% 01 LEDs 03 LEDs 30% 05 LEDs 07 LEDs 20% 09 LEDs 11 LEDs 10% 13 LEDs 15 LEDs 0% 0 10 20 30 Supply Voltage (V) ZXLD1366 Document number: DS31992 Rev. 5 - 2 15 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Typical Operating Conditions (cont.) LED Current vs Vadj 1200 1000 LED Current (mA) 800 600 400 200 0 0 1 2 3 ADJ Pin Voltage (V) R=200mΩ R=300mΩ R=680mΩ Supply current 800 Supply current (mA) 700 600 500 400 Output transistor fully enhanced 300 Output transistor not fully enhanced 200 100 0 0 10 20 30 40 50 60 70 Supply voltage (V) Vref ADJ pin voltage (V) 1.243 1.2425 1.242 1.2415 1.241 1.2405 1.24 1.2395 1.239 1.2385 1.238 0 10 20 30 40 50 60 70 Supply voltage (V) Shutdow n current Shutdown current (mA) 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 Supply voltage (V) ZXLD1366 Document number: DS31992 Rev. 5 - 2 16 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Typical Operating Conditions (cont.) Lx on-resistance vs supply voltage 1.6 On-resistance (Ohms) 1.4 1.2 1 -40C 20C 150C 0.8 0.6 0.4 0.2 0 0 5 10 15 20 25 30 35 Supply Voltage (V) Vadj vs Temperature 1.262 1.26 1.258 Vadj (V) 1.256 7V 9V 12V 20V 30V 1.254 1.252 1.25 1.248 1.246 1.244 -50 0 50 100 Temperature (C) 150 200 Lx on-resistance vs die temperature 1.6 On-resistance (Ohms) 1.4 1.2 1 7V 9V 12V 20V 30V 0.8 0.6 0.4 0.2 0 -50 ZXLD1366 Document number: DS31992 Rev. 5 - 2 0 50 100 Die Temperature (C) 17 of 32 www.diodes.com 150 200 June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Application Information Setting nominal average output current with external resistor RS The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (RS) connected between VIN and ISENSE and is given by: IOUTnom = 0.2/RS [for RS ≥ 0.2V] The table below gives values of nominal average output current for several preferred values of current setting resistor (RS) in the typical application circuit shown on page 1: RS (V) 0.20 0.27 0.56 Nominal average output current (mA) 1000 740 357 The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (=1.25V). Note that RS = 0.2V is the minimum allowed value of sense resistor under these conditions to maintain switch current below the specified maximum value. It is possible to use different values of RS if the ADJ pin is driven from an external voltage. (See next section). Output current adjustment by external DC control voltage The ADJ pin can be driven by an external dc voltage (VADJ), as shown, to adjust the output current to a value above or below the nominal average value defined by RS. + ADJ ZXLD1366 GND DC GND The nominal average output current in this case is given by: IOUTdc = (VADJ /1.25) x (0.2/RS) [for 0.3< VADJ <2.5V] Note that 100% brightness setting corresponds to VADJ = VREF. When driving the ADJ pin above 1.25V, RS must be increased in proportion to prevent IOUTdc exceeding 1A maximum. The input impedance of the ADJ pin is 50kΩ ±25% for voltages below VREF and 14.2kΩ ±25% for voltages above VREF +100mV. ZXLD1366 Document number: DS31992 Rev. 5 - 2 18 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Output current adjustment by PWM control Directly driving ADJ input A Pulse Width Modulated (PWM) signal with duty cycle DPWM can be applied to the ADJ pin, as shown below, to adjust the output current to a value above or below the nominal average value set by resistor RS: PWM VADJ ADJ 0V ZXLD1366 GND GND Driving the ADJ input via open collector transistor The recommended method of driving the ADJ pin and controlling the amplitude of the PWM waveform is to use a small NPN switching transistor as shown below: ADJ PWM ZXLD1366 GND GND This scheme uses the 50k resistor between the ADJ pin and the internal voltage reference as a pull-up resistor for the external transistor. Driving the ADJ input from a microcontroller Another possibility is to drive the device from the open drain output of a microcontroller. The diagram below shows one method of doing this: MCU 3.3k ADJ ZXLD1366 GND If the NMOS transistor within the microcontroller has high Gate / Drain capacitance, this arrangement can inject a negative spike into ADJ input of the ZXLD1366 and cause erratic operation but the addition of a Schottky clamp diode (eg Diodes Inc. SD103CWS) to ground and inclusion of a series resistor (3.3k) will prevent this. See the section on PWM dimming for more details of the various modes of control using high frequency and low frequency PWM signals. ZXLD1366 Document number: DS31992 Rev. 5 - 2 19 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Shutdown mode Taking the ADJ pin to a voltage below 0.2V for more than approximately 100μs will turn off the output and supply current to a low standby level of 65μA nominal. Note that the ADJ pin is not a logic input. Taking the ADJ pin to a voltage above VREF will increase output current above the 100% nominal average value. (See page 18 graphs for details). Soft-start An external capacitor from the ADJ pin to ground will provide a soft-start delay, by increasing the time taken for the voltage on this pin to rise to the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the comparator. Adding capacitance increases this delay by approximately 0.2ms/nF. The graph below shows the variation of soft-start time for different values of capacitor. Soft Start Time vs Capacitance from ADJ pin to Ground 16 14 Soft Start Time (ms) 12 10 8 6 4 2 0 -2 0 20 40 60 Capacitance (nf) 80 100 120 Actual operating waveforms [VIN=60V, RS=0.2V, L=68μH, 22nF on ADJ] Soft-start operation. LX voltage (CH2) and Output current (CH3) using a 22nF external capacitor on the ADJ pin. ZXLD1366 Document number: DS31992 Rev. 5 - 2 20 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 VIN capacitor selection A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with the supply source impedance and lowers overall efficiency. This capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the input supply. To avoid transients into the IC, the size of the input capacitor will depend on the VIN voltage: VIN = 6 to 40V CIN = 2.2μF VIN = 40 to 50V CIN = 4.7μF VIN = 50 to 60V CIN = 10μF When the input voltage is close to the output voltage the input current increases which puts more demand on the input capacitor. The minimum value of 2.2μF may need to be increased to 4.7μF; higher values will improve performance at lower input voltages, especially when the source impedance is high. The input capacitor should be placed as close as possible to the IC. For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric is recommended. Capacitors with Y5V dielectric are not suitable for decoupling in this application and should NOT be used. When higher voltages are used with the CIN = 10μF, an electrolytic capacitor can be used provided that a suitable 1mF ceramic capacitor is also used and positioned as close to the VIN pin as possible. A suitable capacitor would be NACEW100M1006.3x8TR13F (NIC Components). The following web sites are useful when finding alternatives: www.murata.com www.niccomp.com www.kemet.com ZXLD1366 Document number: DS31992 Rev. 5 - 2 21 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Inductor selection Recommended inductor values for the ZXLD1366 are in the range 68 μH to 220 μH. Higher values of inductance are recommended at higher supply voltages in order to minimize errors due to switching delays, which result in increased ripple and lower efficiency. Higher values of inductance also result in a smaller change in output current over the supply voltage range. (see graphs pages 10- 17). The inductor should be mounted as close to the device as possible with low resistance connections to the LX and VIN pins. The chosen coil should have a saturation current higher than the peak output current and a continuous current rating above the required mean output current. Suitable coils for use with the ZXLD1366 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 The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the specified limits over the supply voltage and load current range. The graph Figure 3 below can be used to select a recommended inductor based on maintaining the ZXLD1366 case temperature below 60°C. For detailed performance characteristics for the inductor values 68, 100, 150 and 220μH see graphs on pages 10-17. Minimum Recommended Inductor 2% Accuracy, <60°C Case Temperature 15 Legend 14 68uH 13 100uH 12 150uH Number of LEDs 11 220uH 10 9 8 7 6 5 4 3 2 1 0 10 20 30 40 50 60 Supply Voltage (V) Figure 3 ZXLD1366 Minimum recommended inductor (TSOT23-5) ZXLD1366 Document number: DS31992 Rev. 5 - 2 22 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Figure 4 ZXLD1366 Minimum recommended inductor (DFN3030-6) ZXLD1366Q SO-8-EP Minimum Recommended Inductor 2% Accuracy, <60°C Case Temperature, 1A Target Current 12 Legend 11 47µH 10 68µH 9 100µH . 150µH Number of LEDs 8 220µH 7 6 5 4 3 2 1 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 Supply Voltage (V) Figure 5 ZXLD1366 Minimum recommended inductor (SO-8-EP) ZXLD1366 Document number: DS31992 Rev. 5 - 2 23 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 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. They also provide better efficiency than silicon 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. It is very important to consider the reverse leakage of the diode when operating above 85°C. Excess leakage will increase the power dissipation in the device and if close to the load may create a thermal runaway condition. The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on the LX output. 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 B3100 (Diodes Inc). Reducing output ripple Peak to peak ripple current in the LED(s) can be reduced, if required, by shunting a capacitor Cled across the LED(s) as shown below: D1 VIN Rs LED Cled L1 VIN ISENSE LX ZXLD1366 Figure 6 Reduce Output Ripple A value of 1mF will reduce the supply ripple current by a factor three (approx.). Proportionally lower ripple can be achieved with higher capacitor values. Note that the capacitor will not affect operating frequency or efficiency, but it will increase startup delay, by reducing the rate of rise of LED voltage. By adding this capacitor the current waveform through the LED(s) changes from a triangular ramp to a more sinusoidal version without altering the mean current value. ZXLD1366 Document number: DS31992 Rev. 5 - 2 24 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Operation at low supply voltage Below the under-voltage lockout threshold (VSD) the drive to the output transistor is turned off to prevent device operation with excessive on-resistance of the output transistor. The output transistor is not full enhanced until the supply voltage exceeds approximately 17V. At supply voltages between VSD and 17V care must be taken to avoid excessive power dissipation due to the on-resistance. Note that when driving loads of two or more LEDs, the forward drop will normally be sufficient to prevent the device from switching below approximately 6V. This will minimize the risk of damage to the device. Thermal considerations When operating the device at high ambient temperatures, or when driving maximum load current, care must be taken to avoid exceeding the package power dissipation limits. The graph below gives details for power derating. This assumes the device to be mounted on a 25mm2 PCB with 1oz copper standing in still air. Note that the device power dissipation will most often be a maximum at minimum supply voltage. It will also increase if the efficiency of the circuit is low. This may result from the use of unsuitable coils, or excessive parasitic output capacitance on the switch output. ZXLD1366 Document number: DS31992 Rev. 5 - 2 25 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 In order to maximize the thermal capabilities of the DFN3030-6 and the SO-8-EP packages thermal vias should be incorporated into the PCB. See figures 7 and 8 for examples used in the ZXLD1366 evaluation boards. Figure 7 Suggested layout for DFN3030-6 package Figure 8 Suggested layout for SO-8-EP package Vias ensure an effective path to the ground plane for the heat flow therefore reducing the thermal impedance between junction and ambient temperature. Diodes came to the conclusion that the compromise is reached by using more than 10 vias with 1mm of diameter and 0.5 hole size. Finally the same scheme in figure 7 (without the exposed paddle) can be usde for the TSOT23-5 package guaranteeing an effective thermal path. ZXLD1366 Document number: DS31992 Rev. 5 - 2 26 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Thermal compensation of output current High luminance LEDs often need to be supplied with a temperature compensated current in order to maintain stable and reliable operation at all drive levels. The LEDs are usually mounted remotely from the device so, for this reason, the temperature coefficients of the internal circuits for the ZXLD1366 have been optimized to minimize the change in output current when no compensation is employed. If output current compensation is required, it is possible to use an external temperature sensing network normally using Negative Temperature Coefficient (NTC) thermistors and/or diodes, mounted very close to the LED(s). The output of the sensing network can be used to drive the ADJ pin in order to reduce output current with increasing temperature. Layout considerations LX pin The LX pin of the device is a fast switching node, so PCB tracks should be kept as short as possible. To minimize ground 'bounce', the ground pin of the device should be soldered directly to the ground plane. Coil and decoupling capacitors and current sense resistor It is particularly important to mount the coil and the input decoupling capacitor as close to the device pins as possible to minimize parasitic resistance and inductance, which will degrade efficiency. It is also important to minimize any track resistance in series with current sense resistor RS. Its best to connect VIN directly to one end of RS and ISENSE directly to the opposite end of RS with no other currents flowing in these tracks. It is important that the cathode current of the Schottky diode does not flow in a track between RS and VIN as this may give an apparent higher measure of current than is actual because of track resistance. ADJ pin The ADJ pin is a high impedance input for voltages up to 1.35V so, when left floating, PCB tracks to this pin should be as short as possible to reduce noise pickup. A 100nF capacitor from the ADJ pin to ground will reduce frequency modulation of the output under these conditions. An additional series 3.3kΩ resistor can also be used when driving the ADJ pin from an external circuit (see below). This resistor will provide filtering for low frequency noise and provide protection against high voltage transients. 3.3k ADJ 100nF ZXLD1366 GND GND High voltage tracks Avoid running any high voltage tracks close to the ADJ pin, to reduce the risk of leakage currents due to board contamination. The ADJ pin is soft-clamped for voltages above 1.35V to desensitize it to leakage that might raise the ADJ pin voltage and cause excessive output current. However, a ground ring placed around the ADJ pin is recommended to minimize changes in output current under these conditions. ZXLD1366 Document number: DS31992 Rev. 5 - 2 27 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Evaluation PCB ZXLD1366 evaluation boards are available on request. Terminals allow for interfacing to customers own LED products. Dimming output current using PWM Low frequency PWM mode When the ADJ pin is driven with a low frequency PWM signal (eg 100Hz), with a high level voltage VADJ and a low level of zero, the output of the internal low pass filter will swing between 0V and VADJ, causing the input to the shutdown circuit to fall below its turn-off threshold (200mV nom) when the ADJ pin is low. This will cause the output current to be switched on and off at the PWM frequency, resulting in an average output current IOUTavg proportional to the PWM duty cycle. (See Figure 4 - Low frequency PWM operating waveforms). VADJ Ton PWM Voltage Toff 0V IOUTnom 0.2/Rs Output Current IOUTavg 0 Figure 4 Low frequency PWM operating waveforms The average value of output current in this mode is given by: IOUTavg 0.2DPWM/RS [for DPWM >0.001] This mode is preferable if optimum LED 'whiteness' is required. It will also provide the widest possible dimming range (approx. 1000:1) and higher efficiency at the expense of greater output ripple. ZXLD1366 Document number: DS31992 Rev. 5 - 2 28 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Ordering Information Device Package ZXLD1366ET5TA ZXLD1366DACTC ZXLD1366EN8TC TSOT23-5 DFN3030-6 SO-8-EP Reel size (inches) 7” 13” 13” Reel width (mm) 8 12 12 Quantity Per reel 3000 3000 2500 Device mark 1366 1366 1366 Package Outline Dimensions TSOT23-5 Millimeters Inches Millimeters Dim. Inches Dim. Min. Max. Min. Max. A - 1.00 - 0.0393 E1 1.60 BSC 0.062 BSC A1 0.01 0.10 0.0003 0.0039 e 0.95 BSC 0.037 BSC A2 0.84 0.90 0.0330 0.0354 1.90 BSC 0.074 BSC b 0.30 0.45 0.0118 0.0177 L C 0.12 0.20 0.0047 0.0078 L2 D 2.90 BSC 0.114 BSC E 2.80 BSC 0.110 BSC ZXLD1366 Document number: DS31992 Rev. 5 - 2 Min. Q 29 of 32 www.diodes.com 0.10 Max. 0.60 Min. 0.0039 0.25 BSC 4 Max. 0.0236 0.010 BSC 12 4 12 June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Package Outline Dimensions DFN3030-6 e1 D E E2 L D2 e b PIN 1 DOT BY MARKING BOTTOM VIEW A3 A1 A TOP VIEW PIN #1 IDENTIFICATION CHAMFER 0.300X45° SIDE VIEW DIM Millimeters Inches Min. Max. Min. A 0.700 0.800 0.0275 0.0315 D2 A1 0.000 0.050 0.000 0.00197 e A3 0.203 REF Max. DIM 0.008 Min. Max. Min. Max. 1.950 2.050 0.0768 0.0807 0.950 BSC 0.0374 BSC 2.950 3.050 0.116 1.150 1.250 0.0452 b 0.300 0.400 0.0118 0.0157 E2 2.950 3.050 0.116 0.120 e1 L Document number: DS31992 Rev. 5 - 2 Inches E D ZXLD1366 Millimeters 1.900REF 0.450 30 of 32 www.diodes.com 0.550 0.120 0.0492 0.0748 0.0177 0.0216 June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 Package Outline Dimensions SO-8-EP ZXLD1366 Document number: DS31992 Rev. 5 - 2 31 of 32 www.diodes.com June 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1366 IMPORTANT NOTICE 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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Life support devices or systems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems. Copyright © 2010, Diodes Incorporated www.diodes.com ZXLD1366 Document number: DS31992 Rev. 5 - 2 32 of 32 www.diodes.com June 2010 © Diodes Incorporated