A Product Line of Diodes Incorporated ZXLD1362 60V 1A LED DRIVER WITH AEC-Q100 Description Pin Assignments The ZXLD1362 is a continuous mode inductive step-down converter (Top View) with integrated switch and high side current sense. It operates from an input supply from 6V to 60V driving single or LX multiple series connected LEDs efficiently externally adjustable output current up to 1A. GND The ZXLD1362 has been qualified to AEC-Q100 Grade 1 enabling operation in ambient temperatures from -40°C to +125°C. VIN ISENSE ADJ TSOT25 The output current can be adjusted by applying a DC voltage or a PWM waveform. 100.1 adjustment of output current is possible using PWM control. Applying 0.2V or lower to the ADJ pin turns the output off and switches the device into a low current standby state. Features • Simple low parts count • Single pin on/off and brightness control using DC voltage or PWM • High efficiency (up to 95%) • Wide input voltage range: 6V to 60V • Up to 1MHz switching frequency • Qualified to AEC-Q100 Grade 1 • Typical 2% output current accuracy • Thermally enhanced TSOT25: θJA 82°C/W • Available in Green molding Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2) Halogen and Antimony Free. “Green” Device (Note 3) Notes: 1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant. 2. See http://www.diodes.com for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green" and Lead-free. 3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and <1000ppm antimony compounds. Typical Application Circuit VIN 24V C1 4.7µF RS L1 0.1Ω 68µH VIN ADJ C2 100nF SET LX ZXLD1362 GND GND ZXLD1362 Document number: DS33472 Rev. 5 - 2 1 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Pin Description Name Pin No. LX 1 Drain of NDMOS switch Function GND 2 Ground (0V) Multi-function On/Off and brightness control pin: • Leave floating for normal operation.(VADJ = VREF = 1.25V giving nominal average output current o ADJ IOUTnom = 0.1/RS) • Drive to voltage below 0.2V to turn off output current 3 • 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 increase soft-start time. • Soft-start time increases approximately 200µs/nF. ISENSE 4 VIN 5 Connect resistor RS from this pin to VIN to define nominal average output current IOUTnom = 0.1/RS (Note: RSMIN = 0.1Ω with ADJ pin open circuit) Input voltage (6V to 60V). Decouple to ground with 4.7µF of higher X7R ceramic capacitor close to device. Block Diagram VIN D1 L1 RS ` 5 VIN 5V 1 LX R1 Voltage regulator C1 4.7µF 4 ISENSE 0.2V Low voltage detector GND MN ADJ 3 R4 50k R5 20k R2 D1 1.25V R3 1.35V GND GND 2 Figure 1. Block Diagram ZXLD1362 Document number: DS33472 Rev. 5 - 2 2 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Absolute Maximum Ratings (Note 4) Symbol Rating Unit Input Voltage Parameter -0.3 to +65 V ISENSE Voltage (Note 5) +0.3 to -5 V VLX LX Output Voltage -0.3 to +65 V VADJ Adjust Pin Input Voltage -0.3 to +6 V 1.25 A 1 W VIN VSENSE ILX Switch Output Current Power Dissipation PTOT (Refer to Package thermal de-rating curve on page 16) TST Storage Temperature -55 to +150 °C TJ MAX Junction Temperature 150 °C Note: 4 All voltages unless otherwise stated are measured with respect to GND. 5. VSENSE is measured with respect to VIN. Caution: Stresses greater than the 'Absolute Maximum Ratings' specified above, may cause permanent damage to the device. These are stress ratings only; functional operation of the device at conditions between maximum recommended operating conditions and absolute maximum ratings is not implied. Device reliability may be affected by exposure to absolute maximum rating conditions for extended periods of time. ESD Susceptibility Rating Unit Human Body Model 500 V Machine Model 75 V Caution: 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. The human body model is a 100pF capacitor discharge through a 1.5kΩ resistor pin. The machine model is a 200pF capacitor discharged directly into each pin. Thermal Resistance Symbol Parameter Rating Unit θJA Junction to Ambient 82 °C/W ΨJB Junction to Board 33 °C/W Recommended Operating Conditions Symbol Min Max Units 6 60 V 1 A 0.3 2.5 V DC voltage on ADJ pin to ensure devices is off 0.25 V tONMIN Minimum switch on-time 800 ns fLXmax Recommended maximum operating frequency (Note 8) 625 kHz VIN Input Voltage Range (Note 6) ILX Maximum recommended continuous/RMS switch current VADJ External control voltage range on ADJ pin for DC brightness control (Note 7) VADJoff Notes: Parameter DLX Duty cycle range 0.01 0.99 TA Ambient operating temperature range -40 +125 °C 6. 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. 7. 100% brightness corresponds to VADJ = VADJ(nom) = VREF. Driving the ADJ pin above VREF will increase the VSENSE threshold and output current proportionally. 8. ZXLD1362 will operate at higher frequencies but accuracy will be affected due to propagation delays. ZXLD1362 Document number: DS33472 Rev. 5 - 2 3 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Electrical Characteristics (Test conditions: VIN = 24V, TA = +25°C, unless otherwise specified.) Symbol Parameter Condition Min Typ Max Unit VSU Internal regulator start-up threshold 4.85 V VSD Internal regulator shutdown threshold 4.75 V IINQoff IINQon VSENSE VSENSEHYS ISENSE VREF ΔVREF/ΔT VADJ VADJoff VADJon RADJ ILXmean Quiescent supply current with output off ADJ pin grounded Quiescent supply current with output switching ADJ pin floating, L = 68µH, (Note 9) 3 LEDs, f = 260kHz Mean current sense threshold voltage Measured on ISENSE pin with (Defines LED current setting accuracy) respect to VIN VADJ = 1.25V VSENSE = VIN -0.1 Internal reference voltage Measured on ADJ pin with pin floating DC voltage on ADJ pin to switch device from active VADJ falling (on) state to quiescent (off) state LX switch leakage current 10 µA V ppm/°C 2.5 V 0.15 0.2 0.27 V VADJ rising 0.2 0.25 0.3 V 0 < VADJ < VREF 30 50 65 10.4 14.2 18 VADJ > VREF +100mV Continuous LX switch current ILX(leak) mV % 1.25 0.3 brightness control (Note 7) Resistance between ADJ pin and VREF 105 50 External control voltage range on ADJ pin for DC quiescent (off) state to active (on) state 100 4 Temperature coefficient of VREF LX switch ‘On’ resistance DCADJ 95 µA mA ±10 ISENSE pin input current DC voltage on ADJ pin to switch device from 90 1.8 Sense threshold hysteresis RLX DPWM(LF) 65 @ ILX = 1A Duty cycle range of PWM signal applied to ADJ pin PWM frequency <300Hz during low frequency PWM dimming mode PWM amplitude = VREF Brightness control range Measured on ADJ pin DC Brightness control range Note 10 0.5 0.001 kΩ 1 A 1.0 Ω 5 µA 1 1000:1 5:1 Time taken for output current to reach 90% of final value tSS Soft start time after voltage on ADJ pin has risen above 0.3V. Requires 2 ms 300 kHz external capacitor 22nF. See graphs for more details ADJ pin floating fLX Operating frequency L = 68µH (0.1V) (See graphs for more details) IOUT = 1A @ VLED = 3.6V Driving 3 LEDs tONmin Minimum switch ‘ON’ time LX switch ‘ON’ 130 ns tOFFmin Minimum switch ‘OFF’ time LX switch ‘OFF’ 70 ns Notes: 9. Static current of device is approximately 700µA, see Graph, Page 16. 10. Ratio of maximum brightness to minimum brightness before shutdown VREF = 1.25/0.3. VREF externally driven to 2.5V, ratio 10:1. ZXLD1362 Document number: DS33472 Rev. 5 - 2 4 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 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) Figure 2. Theoretical Operating Waveforms Operation can be best understood by assuming that the ADJ comparator. When this reaches the threshold voltage (VADJ), pin of the device is unconnected and the voltage on this pin (VADJ) appears directly at the (+) input of the comparator. 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 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 hysteresis. The hysteresis is set by R3 to be nominally 10% of VADJ. 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 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 RS, L1 and the LED(s). The current rises at a rate determined determined by the LED(s) and diode forward voltages to by VIN and L1 to produce a voltage ramp (V SENSE ) 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 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 ± 10%. produces a ground referred rising voltage at the (-) input of the ZXLD1362 Document number: DS33472 Rev. 5 - 2 5 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Device Description Switching Thresholds With VADJ = VREF, the ratios of R1, R2 and R3 define an average VSENSE switching threshold of 100mV (measured on the ISENSE pin with respect to VIN). The average output current IOUTnom is then defined by this voltage and RS according to: DC or pulse signals to change the VSENSE switching threshold and adjust the output current. IOUTnom = 100mV/RS Output Shutdown Nominal ripple current is ±10mV/RS 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. 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 Details of the different modes of adjusting output current are given in the applications section. Actual Operating Waveforms VIN = 30V, RS = 0.1V, L = 100µH Normal Operation. Output Current (Ch1) and LX Voltage (Ch2) VIN = 15V, RS = 0.1V, L = 100µH Normal operation. Output Current (Ch1) and LX Voltage (Ch2) VIN = 60V, RS = 0.1V, L = 100µH Normal Operation. Output Current (Ch1) and LX Voltage (Ch2) ZXLD1362 Document number: DS33472 Rev. 5 - 2 6 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Typical Characteristics ZXLD1362 Output Current L = 68µH 1100 1090 1080 Output Current (mA) 1070 1060 1050 1040 1030 1020 1010 1000 0 10 20 30 40 50 60 70 Supply Voltage (V) 1 LED 3 LED 5 LED 7 LED 9 LED 11 LED 13 LED 15 LED ZXLD1362 Output Current L = 68µH 10% 8% Output Current Deviation 6% 4% 2% 0% -2% -4% -6% -8% -10% 0 10 20 30 40 50 60 70 Supply Voltage (V) 1 LED 3 LED 5 LED 7 LED 9 LED 11 LED 13 LED 15 LED ZXLD1362 Efficiency L = 68µH 100% Efficiency (%) 90% 80% 70% 60% 50% 0 10 1 LED ZXLD1362 Document number: DS33472 Rev. 5 - 2 20 3 LED 30 40 Supply Voltage (V) 5 LED 7 LED 9 LED 7 of 24 www.diodes.com 50 11 LED 60 13 LED 70 15 LED May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Typical Characteristics (cont.) ZXLD1362 Switching Frequency L = 68µH 500 Switching Frequency (kHz) 400 300 200 100 0 0 10 1 LED 20 3 LED 5 LED 30 40 Supply Voltage (V) 7 LED 9 LED 50 11 LED 60 13 LED 70 15 LED ZXLD1362 Duty Cycle L = 68µH 100 90 80 Duty Cycle (%) 70 60 50 40 30 20 10 0 0 10 1 LED ZXLD1362 Document number: DS33472 Rev. 5 - 2 20 3 LED 5 LED 30 40 Supply Voltage (V) 7 LED 9 LED 8 of 24 www.diodes.com 50 11 LED 60 13 LED 70 15 LED May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Typical Characteristics (cont.) 1100 ZXLD1362 Output Current L = 100µH 1090 1080 Output Current (mA) 1070 1060 1050 1040 1030 1020 1010 1000 0 10 20 30 40 50 60 70 Supply Voltage (V) 1 LED 3 LED 5 LED 7 LED 9 LED 11 LED 13 LED 15 LED ZXLD1362 Output Current L = 100µH 10% 8% Output Current Deviation 6% 4% 2% 0% -2% -4% -6% -8% -10% 0 10 20 30 40 50 60 11 LED 13 LED 70 Supply Voltage (V) 1 LED 3 LED 5 LED 7 LED 9 LED 15 LED ZXLD1362 Efficiency L = 100µH 100% Efficiency (%) 90% 80% 70% 60% 50% 0 10 1 LED ZXLD1362 Document number: DS33472 Rev. 5 - 2 20 3 LED 5 LED 30 40 Supply Voltage (V) 7 LED 9 LED 9 of 24 www.diodes.com 50 11 LED 60 13 LED 70 15 LED May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Typical Characteristics (cont.) ZXLD1362 Switching Frequency L = 100µH 500 Switching Frequency (kHz) 400 300 200 100 0 0 10 1 LED 20 3 LED 30 40 Supply Voltage (V) 5 LED 7 LED 9 LED 50 11 LED 60 13 LED 70 15 LED ZXLD1362 Switching Frequency L = 100µH 100 90 80 Duty Cycle (%) 70 60 50 40 30 20 10 0 0 10 1 LED ZXLD1362 Document number: DS33472 Rev. 5 - 2 20 3 LED 5 LED 30 40 Supply Voltage (V) 7 LED 9 LED 10 of 24 www.diodes.com 50 11 LED 60 13 LED 70 15 LED May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Typical Characteristics (cont.) ZXLD1362 Output Current L = 150µH 1100 1090 Output Current (mA) 1080 1070 1060 1050 1040 1030 1020 1010 1000 0 10 20 30 40 50 60 70 Supply Voltage (V) 1 LED 3 LED 5 LED 7 LED 9 LED 11 LED 13 LED 15 LED ZXLD1362 Output Current L = 150µH 10% 8% Output Current Deviation 6% 4% 2% 0% -2% -4% -6% -8% -10% 0 10 20 30 40 50 60 70 Supply Voltage (V) 1 LED 3 LED 5 LED 7 LED 9 LED 11 LED 13 LED 15 LED ZXLD1362 Efficiency L = 150µH 100% Efficiency (%) 90% 80% 70% 60% 50% 0 10 20 30 40 50 60 70 Supply Voltage (V) 1 LED ZXLD1362 Document number: DS33472 Rev. 5 - 2 3 LED 5 LED 7 LED 9 LED 11 of 24 www.diodes.com 11 LED 13 LED 15 LED May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Typical Characteristics (cont.) ZXLD1362 Switching Frequency L = 150µH 500 Switching Frequency (kHz) 400 300 200 100 0 0 10 1 LED 20 3 LED 5 LED 30 40 Supply Voltage (V) 7 LED 9 LED 50 60 11 LED 13 LED 50 60 70 15 LED ZXLD1362 Duty Cycle L = 150µH 100 90 80 Duty Cycle (%) 70 60 50 40 30 20 10 0 0 10 1 LED ZXLD1362 Document number: DS33472 Rev. 5 - 2 20 3 LED 5 LED 30 40 Supply Voltage (V) 7 LED 9 LED 12 of 24 www.diodes.com 11 LED 13 LED 70 15 LED May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Typical Characteristics (cont.) ZXLD1362 Output Current L = 220µH 1100 1090 1080 Output Current (mA) 1070 1060 1050 1040 1030 1020 1010 1000 0 10 1 LED 20 3 LED 5 LED 30 40 Supply Voltage (V) 7 LED 9 LED 50 11 LED 60 13 LED 70 15 LED ZXLD1362 Output Current L = 220µH 10% 8% Output Current Deviation 6% 4% 2% 0% -2% -4% -6% -8% -10% 0 10 1 LED 20 3 LED 30 40 Supply Voltage (V) 5 LED 7 LED 9 LED 50 11 LED 60 13 LED 70 15 LED ZXLD1362 Efficiency L = 220µH 100% Efficiency (%) 90% 80% 70% 60% 50% 0 10 1 LED ZXLD1362 Document number: DS33472 Rev. 5 - 2 20 3 LED 5 LED 30 40 Supply Voltage (V) 7 LED 9 LED 13 of 24 www.diodes.com 50 11 LED 60 13 LED 70 15 LED May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Typical Characteristics (cont.) ZXLD1362 Switching Frequency L = 2200µH 500 Switching Frequency (kHz) 400 300 200 100 0 0 10 1 LED 20 3 LED 5 LED 30 40 Supply Voltage (V) 50 7 LED 9 LED ZXLD1362 Duty Cycle L = 2200µH 11 LED 30 40 Supply Voltage (V) 50 60 13 LED 70 15 LED 100 90 80 Duty Cycle (%) 70 60 50 40 30 20 10 0 0 10 1 LED ZXLD1362 Document number: DS33472 Rev. 5 - 2 20 3 LED 5 LED 7 LED 9 LED 14 of 24 www.diodes.com 11 LED 60 13 LED 70 15 LED May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Typical Characteristics (cont.) LED Current vs Vadj 1200 1000 LED Current (mA) 800 600 400 200 0 0 1 2 3 ADJ Pin Voltage (V) R=100mΩ R=150mΩ R=330mΩ Supply current 800 Supply current (mA) 700 600 500 400 300 200 100 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) ZXLD1362 Document number: DS33472 Rev. 5 - 2 15 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Typical Characteristics (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 ZXLD1362 Document number: DS33472 Rev. 5 - 2 0 50 100 Die Temperature (C) 16 of 24 www.diodes.com 150 200 May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Application Information Setting Nominal Average Output Current with External Resistor RS Output Current Adjustment by PWM Control The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (RS) connected A Pulse Width Modulated (PWM) signal with duty cycle DPWM can between VIN and ISENSE and is given by: Directly driving ADJ input be applied to the ADJ pin, as shown below, to adjust the output IOUTnom = 0.1/RS [for RS > 0.1Ω] current to a value above or below the nominal average value set by resistor RS: The table below gives values of nominal average output current for several preferred values of current setting resistor (RS) in the typical VADJ PWM ADJ application circuit shown on page 1: RS (Ω) Nominal average output current (mA) 0.1 1000 0.13 760 0.15 667 ZXLD1362 0V GND GND Driving the ADJ Input via Open Collector Transistor The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (= 1.25V). Note that RS = 0.1Ω is the minimum allowed value of sense resistor under these conditions to 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: 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). ADJ PWM GND 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 ZXLD1362 ZXLD1362 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 GND Another possibility is to drive the device from the open drain output DC of a microcontroller. The diagram below shows one method of doing this: GND MCU 3.3k ADJ The nominal average output current in this case is given by: IOUTdc = (VADJ /1.25) x (100mV/RS) [for 0.3< VADJ <2.5V] ZXLD1362 GND 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. If the NMOS transistor within the microcontroller has high Gate / Drain capacitance, this arrangement can inject a negative spike into ADJ input of the 1362 and cause erratic operation but the addition of a Schottky clamp diode (cathode to ADJ) 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. ZXLD1362 Document number: DS33472 Rev. 5 - 2 17 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Application Information (cont.) Shutdown Mode Soft-Start Taking the ADJ pin to a voltage below 0.2V for more than An external capacitor from the ADJ pin to ground will provide a approximately 100µs will turn off the output and supply current soft-start delay, by increasing the time taken for the voltage on to a low standby level of 20µA nominal. this pin to rise to the turn-on threshold and by slowing down the 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 rate of rise of the control voltage at the input of the comparator. 100% nominal average value. (See page 18 graphs for details). 200µs/nF. The graph to the left shows the variation of soft-start Adding capacitance increases this delay by approximately time for different values of capacitor. Actual Operating Waveforms [VIN = 24V, RS = 0.1Ω, L = 68µH, 22nF on ADJ] 16 Soft-start operation. Output current (Ch2) and LX voltage (Ch1) SOFT START TIME (ms) 14 12 10 8 6 4 2 0 -2 0 20 40 60 80 100 CAPACITANCE (nF) Soft Start Time vs. Capacitance from ADJ Pin to Ground 120 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 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. If higher voltages are used and the CIN is 10μF. This can be an electrolytic capacitor provide a suitable 1µF ceramic capacitor is also used and positioned as close the VIN of the IC as possible. A suitable capacitor would be NACEW100M1006.3x8TR13F. 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 The following web sites are useful when finding alternatives: www.murata.com www.niccomp.com www.kemet.com ZXLD1362 Document number: DS33472 Rev. 5 - 2 18 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Application Information (cont.) Inductor Selection Recommended inductor values for the ZXLD1362 are in the manufactured by NIC components. The following websites may range 68μH to 220μH. be useful in finding suitable components. Higher values of inductance are recommended at higher www.coilcraft.com supply voltages in order to minimize errors due to switching www.niccomp.com delays, which result in increased ripple and lower efficiency. www.wuerth-elektronik.de Higher values of inductance also result in a smaller change in output current over the supply voltage range. (see graphs The inductor value should be chosen to maintain operating pages 10 - 17). The inductor should be mounted as close to duty cycle and switch 'on'/'off' times within the specified limits the device as possible with low resistance connections to the LX and VIN pins. over the supply voltage and load current range. The graph Figure 3 below can be used to select a The chosen coil should have a saturation current higher than recommended inductor based on maintaining the ZXLD1362 the peak output current and a continuous current rating above case temperature below 60°C. For detailed performance the required mean output current. characteristics for the inductor values 68, 100, 150 and 220μH Suitable coils for use with the ZXLD1362 may be selected from see graphs on pages 10-17. the MSS range manufactured by Coilcraft, or the NPIS range ZXLD1362 Minimum Recommended Inductor Aluminium board, 2%Accuracy, <60°C CaseTemperature 16 15 14 13 12 Number of LEDs 11 10 9 8 7 6 5 4 3 2 1 0 0 10 20 30 40 50 60 Supply Voltage (V) Figure 3. ZXLD1362 Minimum Recommended Inductor ZXLD1362 Document number: DS33472 Rev. 5 - 2 19 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Application Information (cont.) Diode Selection For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode* with low dissipation in the device and if close to the load may create a thermal runaway condition. reverse leakage at the maximum operating voltage and The higher forward voltage and overshoot due to reverse temperature. recovery time in silicon diodes will increase the peak voltage They also provide better efficiency than silicon diodes, due to a on the LX output. If a silicon diode is used, care should be combination of lower forward voltage and reduced recovery taken to ensure that the total voltage appearing on the LX pin including supply ripple, does not exceed the specified time. It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher maximum value. *A suitable Schottky diode would be 30BQ100PBF (IR). than the maximum output load current. It is very important to consider the reverse leakage of the diode when operating Reducing Output Ripple above +85°C. Excess leakage will increase the power 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: Rs V IN LED Cled L1 D1 VIN ISE NSE LX ZXLD1362 A value of 1μF will reduce the supply ripple current by a factor with excessive on-resistance of the output transistor. The three (approx.). Proportionally lower ripple can be achieved with higher capacitor values. Note that the capacitor will not output transistor is not full enhanced until the supply voltage exceeds approximately 17V. At supply voltages between VSD affect operating frequency or efficiency, but it will increase and 17V care must be taken to avoid excessive power start-up delay, by reducing the rate of rise of LED voltage. dissipation due to the on-resistance. By adding this capacitor the current waveform through the If the supply voltage is always less than 30V continuous an LED(s) changes from a triangular ramp to a more sinusoidal alternative device is available, the ZXLD1360 or the AL8805. version without altering the mean current value. Note that when driving loads of two or more LEDs, the forward drop will normally be sufficient to prevent the device from Operation at Low Supply Voltage switching below approximately 6V. This will minimize the risk of Below the under-voltage lockout threshold (VSD) the drive to damage to the device. the output transistor is turned off to prevent device operation ZXLD1362 Document number: DS33472 Rev. 5 - 2 20 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Application Information (cont.) Thermal Considerations When operating the device at high ambient temperatures, or graph below gives details for power derating. This assumes the when driving maximum load current, care must be taken to device to be mounted on a 25mm PCB with 1oz copper avoid exceeding the package power dissipation limits. The standing in still air. 2 1100 1000 900 POWER (mW) 800 700 600 500 400 300 200 100 0 -50 -30 -10 10 30 50 70 90 110 130 150 AMBIENT TEMPERATURE (°C) Maximum Power Dissipation 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 Layout Considerations LX Pin unsuitable coils, or excessive parasitic output capacitance on The LX pin of the device is a fast switching node, so PCB the switch output. tracks should be kept as short as possible. To minimize ground 'bounce', the ground pin of the device should be soldered Thermal Compensation of Output Current directly to the ground plane. 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 Coil and Decoupling Capacitors and Current Sense Resistor mounted remotely from the device so, for this reason, the It is particularly important to mount the coil and the input temperature coefficients of the internal circuits for the decoupling capacitor as close to the device pins as possible to ZXLD1362 have been optimized to minimize the change in minimize parasitic resistance and inductance, which will output current when no compensation is employed. If output current compensation is required, it is possible to use an degrade efficiency. It is also important to minimize any track resistance in series with current sense resistor RS. Its best to external temperature sensing network - normally using connect VIN directly to one end of RS and ISENSE directly to the Negative Temperature Coefficient (NTC) thermistors and/or opposite end of RS with no other currents flowing in these 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 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 reduce output current with increasing temperature. give an apparent higher measure of current than is actual because of track resistance. ZXLD1362 Document number: DS33472 Rev. 5 - 2 21 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Application Information (cont.) ADJ Pin Dimming Output Current Using PWM The ADJ pin is a high impedance input for voltages up to 1.35V Low Frequency PWM Mode 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 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 also be used when driving the ADJ pin from an external circuit zero, the output of the internal low pass filter will swing between 0V and VADJ, causing the input to the shutdown circuit (see below). This resistor will provide filtering for low frequency to fall below its turn-off threshold (200mV nom) when the ADJ noise and provide protection against high voltage transients. pin is low. This will cause the output current to be switched on under these conditions. An additional series 3.3kΩ resistor can 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). 3.3k ADJ 100nF ZXLD1362 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. Evaluation PCB ZXLD1362 evaluation boards are available on request and provide quick testing of the ZXLD1362 device. Figure 4. Low Frequency PWM Operating Waveforms The average value of output current in this mode is given by: IOUTavg = 0.1DPWM/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. ZXLD1362 Document number: DS33472 Rev. 5 - 2 22 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 Ordering Information Device Part Mark ZXLD1362ET5TA Note: 1362 Package Packaging Reel size Reel width Quantity Part Number AEC-Q100 Code (Note 11) (mm) (mm) per reel Suffix grade ET5 TSOT25 180 8 3000 TA 1 11. Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at http://www.diodes.com/datasheets/ap02001.pdf. Package Outline Dimensions TSOT25 D e1 E E1 L2 c 4x θ1 e L θ 5x b A A2 A1 TSOT25 Dim Min Max Typ A 1.00 − − A1 0.01 0.10 − A2 0.84 0.90 − D 2.90 − − E 2.80 − − E1 1.60 − − b 0.30 0.45 − c 0.12 0.20 − e 0.95 − − e1 1.90 − − L 0.30 0.50 L2 0.25 − − θ 0° 8° 4° θ1 4° 12° − All Dimensions in mm Suggested Pad Layout TSOT25 C C Dimensions Value (in mm) C 0.950 X 0.700 Y 1.000 Y1 3.199 Y1 Y (5x) X (5x) ZXLD1362 Document number: DS33472 Rev. 5 - 2 23 of 24 www.diodes.com May 2012 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1362 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. 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