A Product Line of Diodes Incorporated ZXLD1356 60V 550mA LED DRIVER with AEC-Q100 Description Pin Assignments The ZXLD1356 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 550mA. Depending upon supply voltage and external components, this can provide up to 30 watts of output power. The ZXLD1356 has been qualified to AECQ100 Grade 1 enabling operation in ambient temperatures from -40 to 125C Output current can be adjusted above, or below the set value, by applying an external control signal to the 'ADJ' pin. Enhanced output current dimming can be achieved by applying a PWM signal to the `ADJ' pin. GND ADJ ISENSE TSOT23-5 Top View (TOP VIEW) 6 VIN LX 1 Features * Typically better than 0.8% output current accuracy * 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 * Available in thermally enhanced packages o DFN3030-6 JA 44 C/W o TSOT23-5 JA 82 C/W * Available in Green molding (no Br, Sb) with lead free finish/RoHS compliant * Qualified to AEC-Q100 Grade 1 o TSOT23-5 ZXLD1356ET5TA VIN LX GND 2 5 GND ADJ 3 4 ISENSE DFN3030-6 Typical Application Circuit D1 Rs VIN (24V) 0.36V L1 C1 4.7F Applications * * * * * * * * Low voltage halogen replacement LEDs Automotive lighting Low voltage industrial lighting LED back-up lighting Illuminated signs Emergency lighting SELV lighting Refrigeration lights ZXLD1356 Document number: DS33470 Rev. 3 - 2 100nF VIN I SENSE ADJ ZXLD1356 LX GND GND 1 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Block Diagram D1 VIN L1 RS 5 5V C1 4.7F 4 VIN ISENSE 1 LX R1 Voltage regulator + 0.2V + Low voltage detector MN + Adj 3 R4 50K D1 1.25V Gnd R5 20K 600KHz R2 + R3 1.35V 2 Figure 1. Block diagram - Pin connections shown for TSOT23-5 package Name LX GND TSOT23-5 1 2 DFN3030-6 1 2, 5 ADJ 3 3 ISENSE 4 4 VIN 5 6 Pad - Pad ZXLD1356 Document number: DS33470 Rev. 3 - 2 Description 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 o 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 24% to 200% of IOUTnom * Connect a capacitor from this pin to ground to define soft-start time. Soft-start time is approx.0.2ms/nF Connect resistor RS from this to VIN to define nominal average output current IOUTnom = 0.2/RS (Note: RSMIN=0.36V with ADJ pin open circuit) Input voltage (6V to 60V). Decouple to ground with 4.7F of higher X7R ceramic capacitor close to device Exposed pad (EP) - connected to device substrate. To improve thermal impedance of package the EP must be connected to power ground but should not be used as the 0V (GND) current path. It can be left floating but must not be connected to any other voltage other than 0V. 2 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated) Symbol Parameter VIN Input Voltage VSENSE ISENSE Voltage V +0.3 to -5 (measured with respect to VIN) -0.3 to +60 LX Output Voltage VADJ ILX Adjust Pin Input Voltage Switch Output Current TST TJ MAX Unit (65V for 0.5 sec) VLX PTOT Rating -0.3 to +60 V (65V for 0.5 sec) -0.3 to +6 0.65 Power Dissipation TSOT23-5 1 (Refer to Package thermal de-rating curve on page 25) DFN3030-6 1.8 V V A W Storage Temperature Junction Temperature -55 to 150 150 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. ESD Susceptibility Human Body Model Machine Model Rating 500 <100 Unit V V 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 1.5k resistor pin. The machine model is a 200pF capacitor discharged directly into each pin Thermal Resistance Symbol Parameter JA Junction to Ambient TSOT23-5 82 Rating DFN3030-6 44 Unit C/W JB Junction to Board 33 - JC Junction to Case - 14 C/W Min 6 Max 60 800 800 625 0.99 125 Units V ns ns kHz C/W Recommended Operating Conditions Symbol VIN tOFFMIN tONMIN fLX max DLX TOP Notes: Parameter Input voltage (Note 1) Minimum switch off-time Minimum switch on-time Recommended maximum operating frequency (Note 2) Duty cycle range Operating Temperature range 0.01 -40 C 1. 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. 2. ZXLD1356 will operate at higher frequencies but accuracy will be affected due to propagation delays. ZXLD1356 Document number: DS33470 Rev. 3 - 2 3 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Electrical Characteristics (Test conditions: VIN = 12V, Tamb = 25C, unless otherwise specified.) Symbol VSU VSD IINQoff Parameter Internal regulator start-up threshold Internal regulator shutdown threshold Quiescent supply current with output off IINQon Quiescent supply current with output switching (Note 3) VSENSE Mean current sense threshold voltage (Defines LED current setting accuracy) VSENSEHYS ISENSE Sense threshold hysteresis ISENSE pin input current VREF Internal reference voltage VREF/T Temperature coefficient of VREF External control voltage range on ADJ pin for DC brightness control (Note 4) DC voltage on ADJ pin to switch device from active (on) state to quiescent (off) state DC voltage on ADJ pin to switch device from quiescent (off) state to active (on) state VADJ VADJoff VADJon Condition 4.4 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 DCADJ (*) DC Brightness control range tSS Start up time (See graphs for more details) fLX Operating frequency (See graphs for more details) fLXmax Notes: ADJ pin grounded ADJ pin floating, L=68mH, 3 LEDs f=360kHz Measured on ISENSE pin with respect to VIN VADJ=1.25V; VIN=18V Typ. 4.85 4.75 65 Max. 5.2 108 1.6 195 200 15 4 VSENSE=VIN-0.2 Measured on ADJ pin with pin floating RADJ DPWM(LF) Min. Unit V V A mA 205 mV 10 % A 1.25 V 50 ppm/C 0.3 2.5 V VADJ falling 0.15 0.2 0.27 V VADJ rising 0.2 0.25 0.3 V 0< VADJ< VREF VADJ>VREF +100mV 30 10.4 50 14.2 65 18 0.55 0.75 5 @ ILX=0.55A PWM frequency <300Hz PWM amplitude =VREF Measured on ADJ pin Note 5 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. ADJ pin floating L=68mH (0.36V) IOUT=0.55A @ VLED=3.6V Driving 3 LEDs Recommended maximum operating frequency 0.5 0.001 k A A 1 1000:1 5:1 2 ms 360 kHz 500 kHz 3. Static current of device is approximately 700 A, see Graph, Page 17. 4. 100% brightness corresponds to VADJ = VADJ(nom) = VREF. Driving the ADJ pin above VREF will increase the VSENSE. threshold and output current proportionally. 5. Ratio of maximum brightness to minimum brightness before shutdown VREF =1.25/0.25. VREF externally driven to 2.5V, ratio 10.1. ZXLD1356 Document number: DS33470 Rev. 3 - 2 4 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 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) VIN LX voltage 0V Toff Ton VIN 230mV 170mV 200mV SENSE voltage 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 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%. ZXLD1356 Document number: DS33470 Rev. 3 - 2 5 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Device Description (Continued) 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 (50k 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 60A and switch leakage is below 5A. ZXLD1356 Document number: DS33470 Rev. 3 - 2 6 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Actual operating waveforms [VIN=15V, RS=0.36V, L=68H] Normal operation. Output current (Ch3) and LX voltage (Ch2) Actual operating waveforms [VIN=30V, RS=0.36V, L=68H] Normal operation. Output current (Ch3) and LX voltage (Ch2) Actual operating waveforms [VIN=60V, RS=0.36V, L=68H] Normal operation. Output current (Ch3) and LX voltage (Ch2) ZXLD1356 Document number: DS33470 Rev. 3 - 2 7 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Typical Operating Conditions ZXLD1356 Output Current L = 68H 0.640 0.620 Output Current (A) 0.600 0.580 0.560 0.540 0.520 0.500 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs ZXLD1356 Output Current Deviation (Normalized) L = 68H 10% Output Current Deviation (%) 8% 6% 4% 2% 0% -2% -4% -6% -8% -10% 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs ZXLD1356 Efficiency L = 68H 100% 95% 90% Efficiency (%) 85% 80% 75% 70% 65% 60% 55% 50% 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED ZXLD1356 Document number: DS33470 Rev. 3 - 2 3 LEDs 5 LEDs 7 LEDs 9 LEDs 8 of 29 www.diodes.com 11 LEDs 13 LEDs 15 LEDs December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Typical Operating Conditions (Cont.) ZXLD1356 Switching Frequency L = 68H 700 Switching Frequency (kHz) 600 500 400 300 200 100 0 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs ZXLD1356 Duty Cycle L = 68H 100 90 80 Duty Cycle (% ) 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED ZXLD1356 Document number: DS33470 Rev. 3 - 2 3 LEDs 5 LEDs 7 LEDs 9 LEDs 9 of 29 www.diodes.com 11 LEDs 13 LEDs 15 LEDs December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Typical Operating Conditions (Cont.) ZXLD1356 Output Current L = 100H 0.640 0.620 Output Current (A) 0.600 0.580 0.560 0.540 0.520 0.500 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LED s 15 LED s ZXLD1356 Output Current Deviation (N ormalized) L = 100H 10% Output Current Deviation (%) 8% 6% 4% 2% 0% -2% -4% -6% -8% -10% 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LED s 15 LED s ZXLD1356 Efficiency L = 100H 100% 95% 90% Efficiency (%) 85% 80% 75% 70% 65% 60% 55% 50% 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED ZXLD1356 Document number: DS33470 Rev. 3 - 2 3 LEDs 5 LEDs 7 LEDs 9 LEDs 10 of 29 www.diodes.com 11 LEDs 13 LEDs 15 LEDs December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Typical Operating Conditions (Cont.) ZXLD1356 Switching Frequency L = 100H 700 Switching Frequency (kHz) 600 500 400 300 200 100 0 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs ZXLD1356 Duty Cycle L = 100H 100 90 80 Duty Cycle (%) 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED ZXLD1356 Document number: DS33470 Rev. 3 - 2 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 of 29 www.diodes.com 11 LEDs 13 LEDs 15 LEDs December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Typical Operating Conditions (Cont.) ZXLD1356 Output Current L = 150H 0.640 0.620 Output Current (A) 0.600 0.580 0.560 0.540 0.520 0.500 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs ZXLD 1356 Output Current Deviation (Normalized) L = 150H 10% Output Current Deviation (%) 8% 6% 4% 2% 0% -2% -4% -6% -8% -10% 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs ZXLD1356 Efficiency L = 150H 100% 95% 90% Efficiency (%) 85% 80% 75% 70% 65% 60% 55% 50% 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED ZXLD1356 Document number: DS33470 Rev. 3 - 2 3 LEDs 5 LEDs 7 LEDs 9 LEDs 12 of 29 www.diodes.com 11 LEDs 13 LEDs 15 LEDs December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Typical Operating Conditions (Cont.) ZXLD1356 Switching Frequency L = 150H 700 Switching Frequency (kHz) 600 500 400 300 200 100 0 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LED s 15 LED s ZXLD1356 Duty Cycle L = 150H 100 90 80 Duty Cycle (%) 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED ZXLD1356 Document number: DS33470 Rev. 3 - 2 3 LEDs 5 LEDs 7 LEDs 9 LEDs 13 of 29 www.diodes.com 11 LEDs 13 LEDs 15 LEDs December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Typical Operating Conditions (Cont.) ZXLD1356 Output Current L = 220H 0.640 0.620 Output Current (A) 0.600 0.580 0.560 0.540 0.520 0.500 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs ZXLD1356 Output Current Deviation (N ormalized) L = 220H 10% Output Current Deviation (%) 8% 6% 4% 2% 0% -2% -4% -6% -8% -10% 0 10 20 30 40 50 60 Supply Voltage (V) 1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs ZXLD1356 Efficiency L = 220H 100% 95% 90% Efficiency (%) 85% 80% 75% 70% 65% 60% 55% 50% 0 10 1 LED ZXLD1356 Document number: DS33470 Rev. 3 - 2 3 LEDs 20 5 LEDs 30 Supply Voltage (V) 7 LEDs 9 LEDs 14 of 29 www.diodes.com 40 11 LEDs 50 13 LEDs 60 15 LEDs December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Typical Operating Conditions (Cont.) ZXLD1356 Switching Frequency L = 220H 700 Switching Frequency (kHz) 600 500 400 300 200 100 0 0 10 1 LED 3 LEDs 20 5 LEDs 30 Supply Voltage (V) 7 LEDs 40 9 LEDs 11 LEDs 50 13 LEDs 60 15 LEDs ZXLD1356 Duty Cycle L = 220H 100 90 80 Duty Cycle (%) 70 60 50 40 30 20 10 0 0 10 1 LED ZXLD1356 Document number: DS33470 Rev. 3 - 2 3 LEDs 20 5 LEDs 30 Supply Voltage (V) 7 LEDs 9 LEDs 15 of 29 www.diodes.com 40 11 LEDs 50 13 LED s 60 15 LEDs December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Typical Operating Conditions (Cont.) LED Current vs Vadj 600 500 LED Current (mA) 400 300 200 100 0 0 1 2 3 ADJ Pin Voltage (V) R=0.36 R=0.56 R=1.33 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) Shutdown 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) ZXLD1356 Document number: DS33470 Rev. 3 - 2 16 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Typical Operating Conditions (Cont.) Lx on-resistance vs supply voltage 2.5 O n -resistan ce (O h m s) 2 1.5 -40 oC 25 oC 125 oC 1 0.5 0 0 10 20 30 40 50 60 70 S u p p ly V o ltag e (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 ZXLD1356 Document number: DS33470 Rev. 3 - 2 0 50 100 Die Temperature (C) 17 of 29 www.diodes.com 150 200 December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 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 > 0.36] 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 () Nominal average output current (mA) 0.36 555 0.56 357 1.33 150 The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (=1.25V). Note that RS = 0.36V 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 ZXLD1356 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 550mA maximum. The input impedance of the ADJ pin is 50k 25% for voltages below VREF and 14.2k 25% for voltages above VREF +100mV. ZXLD1356 Document number: DS33470 Rev. 3 - 2 18 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Application Information (Continued) 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 ZXLD1356 0V 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 ZXLD1356 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 eg MMBT3904. 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 ZXLD1356 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 ZXLD1356 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. ZXLD1356 Document number: DS33470 Rev. 3 - 2 19 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Application Information (Continued) Shutdown Mode Taking the ADJ pin to a voltage below 0.2V for more than approximately 100s will turn off the output and supply current to a low standby level of 65A 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 17 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=0.36V, L=68H, 22nF on ADJ] Soft-start operation. LX voltage (Ch2) and Output current (Ch3) using a 22nF external capacitor on the ADJ pin. ZXLD1356 Document number: DS33470 Rev. 3 - 2 20 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Application Information (Continued) 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 = 2.2F VIN = 40 to 50V CIN = 4.7F VIN = 50 to 60V CIN = 10F 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 2.2F may need to be increased to 4.7F; 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 with CIN = 10F, 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 ZXLD1356 Document number: DS33470 Rev. 3 - 2 21 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Application Information (Continued) Inductor Selection Recommended inductor values for the ZXLD1356 are in the range 68 H to 220 H. 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 10-16). 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 ZXLD1356 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. Figures 3 and 4 (following) can be used to select a recommended inductor based on maintaining the ZXLD1356 case temperature below 60C for the different package types. For detailed performance characteristics for the inductor values 68, 100, 150 and 220H see graphs on pages 10-16. Minimum Recommended Inductor 2% Accuracy, <60C 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. ZXLD1356 Minimum Recommended Inductor ZXLD1356 Document number: DS33470 Rev. 3 - 2 22 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Application Information (Continued) 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 85C. 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 B1100B (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 Rs VIN LED Cled L1 V IN ISENSE LX ZXLD1356 A value of 1F 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 start-up 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. 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. ZXLD1356 Document number: DS33470 Rev. 3 - 2 23 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Application Information (Continued) 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 (25mm)2 PCB with 1oz copper standing in still air. Maximum Power Dissipation 2 1.8 DFN3030-6 Power Dissipation (W) 1.6 1.4 1.2 1 0.8 TSOT23-5 0.6 0.4 0.2 0 -40 -25 -10 5 20 35 50 65 Ambient Temperature (C) 80 95 110 125 140 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. 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 ZXLD1356 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. ZXLD1356 Document number: DS33470 Rev. 3 - 2 24 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Application information (Continued) 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 3.3k 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 ZXLD1356 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 Boards ZXLD1356 evaluation boards are available on request, which have connection terminals that allow customers to connect their own LED products to the board. ZXLD1356 Document number: DS33470 Rev. 3 - 2 25 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Application Information (Continued) 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). 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. ZXLD1356 Document number: DS33470 Rev. 3 - 2 26 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Ordering Information Device Part Package mark Code ZXLD1356DACTC 1356 ZXLD1356ET5TA 1356 DAC ET5 Packaging (Note 4) DFN3030-6 TSOT23-5 Reel size (inches) Reel width (mm) 13 7 12 8 Part Quantity per reel Number Suffix 3000 TC 3000 TA AEC-Q100 Grade 1 Package Outline Dimensions TSOT23-5 ZXLD1356 Document number: DS33470 Rev. 3 - 2 27 of 29 www.diodes.com December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 Package Outline Dimensions (Continued) DFN3030-6 e1 D E E2 L D2 b PIN 1 DOT BY MARKING BOTTOM VIEW A3 A1 A TOP VIEW PIN #1 IDENTIFICATION CHAMFER 0.300X45 e SIDE VIEW DIM Millimeters Inches DIM Min. Max. Min. Max. A 0.700 0.800 0.0275 0.0315 D2 A1 0.000 0.050 0.000 0.00197 e A3 0.203 REF 0.008 Millimeters Inches Min. Max. Min. Max. 1.950 2.050 0.0768 0.0807 0.950 BSC 0.0374 BSC E 2.950 3.050 0.116 0.120 b 0.300 0.400 0.0118 0.0157 E2 1.150 1.250 0.0452 0.0492 D 2.950 3.050 0.116 0.120 e1 L ZXLD1356 Document number: DS33470 Rev. 3 - 2 1.900REF 0.450 0.550 28 of 29 www.diodes.com 0.0748 0.0177 0.0216 December 2010 (c) Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1356 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). Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes without further notice to this document and any product described herein. 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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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