A Product Line of Diodes Incorporated ZXLD383 Single or multi cell LED driver with enable/rectifier input for solar charged lamp applications Description Summary The ZXLD383 is a single or multi cell LED driver designed for applications requiring step-up voltage conversion from a very low input voltage. The IC generates constant current pulses that are ideal for driving single or multiple LEDs over a wide range of operating voltages. It includes an on/off enable input that can be driven directly from a photocell array or an open collector/drain logic output. The enable input features an ultra-low voltage drop diode to ground, eliminating the need for a photocell array isolation diode in Garden Light applications. The ZXLD383 uses a PFM control technique to drive an internal switching transistor which exhibits a low saturation resistance. This ensures high efficiency, even for input voltages as low as 1.0V. Features Applications • 85% efficiency • Garden lights • User adjustable output current • Door/pathway illumination • Single cell operation • LED flashlight and torches • Low saturation voltage • LED backlights • TSOT23-5 package • White LED driver • Available also in die form • Gated boost supply generator • Simple application circuit The IC can start up under full load and operates down to an input voltage of below 0.9V. The ZXLD383 is offered in the space saving TSOT23-5 package or in die form, offering an excellent cost vs performance solution for single cell LED driving applications. Z XLD 383 EN A 5 1 VC C D iode A rray GN D NC L1 2 3 4 VOU T N I MH 1. 2V LE D Issue 1 - September 2008 © Diodes Incorporated, 2008 1 www.zetex.com www.diodes.com ZXLD383 Absolute maximum ratings Supply Voltage (Vcc) Output Voltage (Vout) Enable Voltage (Vena) Supply Current Output Switch Current Power Dissipation (TSOT23-5) Power Dissipation Die Operating Temperature Range Storage Temperature Range -0.6V to 6V -0.6V to 20V -1V to 3.5V 20mA 800mA 450mW 1W -20°C to +85°C -55°C to +150°C Electrical Characteristics Measured at TAMB = 25°C, L = 6.8uH, IENA = 0 and VCC = 1.5V unless otherwise specified. Parameter Conditions Supply Voltage Operating Range Minimum Supply Start-up Voltage Supply Current Quiescent Supply Current Shutdown Supply Current Under-Voltage L = 10uH Switch Current Switch Saturation Voltage Switch Leakage Current Mean LED Current Efficiency At turn-off IOUT = 200mA Operating Frequency Discharge Pulse Width VLED = 3.5V Enable Input Threshold Enable Input Current Enable Input Voltage L = 10uH 2 VENA = VCC – 0.8V Limits Typ 250 V 0.8 0.9 V 4 8 mA 17 30 uA 20 uA 400 300 mA mV 10 uA 65 mA % 320 100 VOUT = 20V, VENA = 0V VLED = 3.5V VLED = 3.5V 40 Units Max 3.3 VCC = 0.6V 50 85 330 kHz 0.7 1.5 2.5 us VCC - VCC - VCC - V VENA = 0.2V 0.8 0 0.6 -11 0.2 -20 uA IENA = -20mA 0 -90 -250 mV Issue 1 - September 2008 © Diodes Incorporated Min 0.9 2 www.zetex.com www.diodes.com ZXLD383 Typical characteristics ZX L D383 Efficie n cy vs V C C ZX L D383 I O U T(AV E R AG E ) vs V C C 90 100 80 90 80 70 70 4.7uH Efficien cy (% ) I OU T (m A ) 60 6.8uH 50 10uH 40 22uH 4.7uH 60 6.8uH 10uH 50 22uH 40 47uH 47uH 30 30 20 20 10 10 0 0 0.8 1 1.2 1.4 1.6 1.8 0.8 2 1 1.2 1.4 1.6 1.8 2 V C C (V ) V C C (V ) ZX L D383 I IN vs V C C ZX LD383 P e a k_I IN vs V C C 250 500 450 200 400 350 4.7uH 150 4.7uH 300 I IN ( m A ) I IN ( m A ) 6.8uH 10uH 22uH 100 6.8uH 250 10uH 22uH 200 47uH 47uH 150 50 100 50 0 0 0.8 1 1.2 1.4 1.6 1.8 2 0.8 V C C (V ) 1 1.2 1.4 1.6 1.8 2 V C C (V ) ZX LD383 V ( E N A) vs I E N A For V CC = 0.8, 1.0, 1.2 a nd 1.4V Z X L D 38 3 O p era tin g W a vefo rm s fo r L = 6.8u H , V C C = 1.5V 450 400 350 V E NA (m V) 300 0.8V 250 1.0V 200 1.2V 1.4V 150 100 50 Channel -1 (Upper): I LED@ 100mA/cm Channel -2 (Lower): VOUT@ 1V/cm Timebase: 500ns/cm 0 0 10 20 30 40 50 IV E N A (m A ) Note VLED = 3.5V for all graphs Issue 1 - September 2008 © Diodes Incorporated 3 www.zetex.com www.diodes.com ZXLD383 Device description The ZXLD383 is a simple PFM, DC-DC controller combined with a high performance internal switching transistor, enabling the production of a high efficiency boost converter for use in single cell applications. It includes a dual function Enable input which serves both as an operation inhibit control and an ultra-low voltage drop isolation diode for battery charging purposes in Garden Light applications. A block diagram is shown for the ZXLD383 in Figure 1. VC C L1 Z XLD 383 D iode A rray VOU T EN A P uls e C ont rol N I MH 1. 2V LE D Dch C on Cof f R s ens e GN D Figure 1 - ZXLD383 block diagram With power applied and the enable pin held at VCC, an oscillator within the pulse control block forces the internal switching transistor to switch on to start an energy charge cycle. The low saturation voltage switch pulls the VOUT pin close to ground which forces the supply voltage across the external inductor L1. This causes a current to build up, storing energy in the inductor. During this phase, switch current and supply voltage are monitored and used by the pulse control circuit to determine the optimum drive conditions and on-time. At the end of the energy charge cycle, the internal switch is turned off rapidly, interrupting the current flow through L1 which causes the voltage on VOUT to rise dramatically. When the voltage on VOUT reaches the load LED’s forward (on) voltage, the inductor current is transferred from the internal switch to the LED, starting the energy discharge cycle. With the voltage across the inductor reversed, the current flowing through it (and the LED) now falls. When the inductor current reaches zero, the voltage on the VOUT pin falls back towards VCC. This action is sensed by the pulse control circuit and is combined with the output of an off-period timer to initiate the next energy charge cycle. Except for low level losses, all the energy stored in the inductor during a charge cycle is channelled to the load LED during the following discharge cycle. The current fed into the load LED has a sawtooth waveform, the average (DC) value of which is kept constant by the pulse control circuit for varying supply voltage and temperature. It is possible to change the output current given by the ZXLD383 by changing the value of inductor L1. The larger the inductance of L1, the lower the output current. A table/graph showing the relationship between inductance and output current is given later in this datasheet. Since the Issue 1 - September 2008 © Diodes Incorporated 4 www.zetex.com www.diodes.com ZXLD383 output current of the ZXLD383 is a sawtooth waveform, its peak value is substantially larger than the DC/average value. The table also provides this data. The internal switching transistor has a minimum collector-emitter breakdown voltage of 20V and this sets the maximum load voltage allowable. The minimum value is set by a feature of the pulse control circuit that requires the load voltage to be at least 0.5V greater than VCC. (The device will function with load voltages smaller than this but output current regulation will be impaired.) Higher than nominal load voltages will lower the average (DC) output current generated for a given inductor value. The Enable pin inhibits the operation of the output switch if held at a potential of Vcc-0.8V or lower. It also includes a diode to ground which allows the input to be wired directly to a photocell array that will then both enable operation of the converter when in darkness and charge the IC’s power source in daylight conditions. The diode function is performed by an active circuit that gives an ultra low forward voltage drop (typically less than 0.1V at 20mA). This allows the use of a lower output voltage photocell array (lower cost) without degrading performance. Application Examples Apart from the Garden Light application circuit shown on the front page of this datasheet, the ZXLD383 may be used in many other ways. The following circuits and notes show some other possibilities and give typical performance details. Standard operating mode The following circuit demonstrates how few components are required to produce a light source using the ZXLD383. Operating from a single cell, this simple circuit is suited for use in car key fobs, novelty products etc. where small size and low cost are critical aspects. By directly wiring the Ena pin to Vcc, the part is permanently enabled once a power supply is provided. The ZXLD383 is highly tolerant of supply ripple so no decoupling of Vcc should be needed in a compactly constructed circuit. Also, the part’s capability of operating with a Vcc below 0.9V means that this simple circuit will make the best use of available battery capacity. The attached table shows the average LED currents that can be obtained using a range of inductor values. Also shown are the peak currents required to achieve the given currents. Z XLD 383 EN A GN D NC 1 5 I LE D (peak ) I LE D (avg) (uH ) (m A ) (m A ) L1 2 3 L VC C 4 VOU T 1. 5V LE D 47 45 8.5 22 100 17.3 10 210 34 6.8 330 50 4.7 415 63 Note VLED = 3.5V Issue 1 - September 2008 © Diodes Incorporated 5 www.zetex.com www.diodes.com ZXLD383 Low ripple LED current mode It is possible that the peak LED current required to achieve a given average current is either too high for the LED of choice or it leads to some loss of efficiency (due to LED resistance losses). In these cases, just two extra low cost components can be added to provide a low ripple current supply for the LED. The Schottky diode D1 and capacitor C1 rectifies and smoothes the output of the ZXLD383 giving a low ripple current supply to the load LED. Of course, this circuit could also be used to power loads other than LEDs. Z XLD 383 EN A GN D 1 5 VC C L1 2 D1 NC 4 3 VOU T C1 1. 5V LE D L I LE D (uH ) (m A ) 47 7.5 22 15.5 10 31 6.8 46 4.7 58 Note: VLED =3.5V, D1=ZHCS1000, C1 = 1uF (low ESR) Buck-boost mode Simple boost converters can run into problems when the input supply voltage is similar to or exceeds the intended load voltage as there is usually a direct current path from the power source through to the load via the boost inductor. This path does not require switching action and so is uncontrolled. When using the ZXLD383, this problem can be avoided by wiring the cathode of the load LED to Vcc rather than ground. Without switching action, the LED is reverse-biased and so no current can flow. When switching, the anode of the LED is driven to Vcc + Vf(led). The higher than normal output voltage reduces the available output current as described earlier and this is shown in the typical data provided. LE D Z XLD 383 3V EN A GN D NC 1 5 VC C L1 2 3 4 L ILE D (uH ) (m A ) 47 5.5 22 10.3 10 23.2 6.8 36.7 4.7 46.2 VOU T Note: VLED =3.5V Issue 1 - September 2008 © Diodes Incorporated 6 www.zetex.com www.diodes.com ZXLD383 Low ripple buck-boost mode The output of the Buck-Boost converter can be rectified and smoothed as with the standard circuit to give a low ripple output to improve LED efficiency or to give a DC output for other loads. C1 LE D Z XLD 383 3V EN A GN D 1 5 VC C L1 2 L ILE D (uH ) (m A ) 47 5 22 9.7 10 21.7 6.8 34 4.7 43 D1 NC 3 4 VOU T Note: VLED =3.5V, D1=ZHCS1000, C1 = 1uF (low ESR) Issue 1 - September 2008 © Diodes Incorporated 7 www.zetex.com www.diodes.com ZXLD383 Pin descriptions Pin No. 1 2 3 4 5 Name ENA GND NC VOUT VCC Description Enable / Photodiode array battery charge input Ground Not connected (internally open circuit) Switch output external inductor/LED Supply voltage, generally Alkaline, NiMH or NiCd single cell Pinout diagram ZXLD383 ENA 1 5 VCC 4 VOUT GND 2 NC 3 TSOT23-5 Top view Ordering information Device Reel size (inches) Reel width (mm) Quantity per reel Device mark 7” 8 3,000 383 ZXLD383ET5TA Issue 1 - September 2008 © Diodes Incorporated 8 www.zetex.com www.diodes.com ZXLD383 Packaging information - TSOT23-5 Dim. Millimeters Inches Dim. Millimeters Min. Max. Inches Min. Max. 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 e1 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 Issue 1 - September 2008 © Diodes Incorporated Q 9 0.10 0.60 0.25 BSC 4o 12o 0.0039 0.0236 0.010 BSC 4o 12o www.zetex.com www.diodes.com ZXLD383 Definitions Product change Diodes Incorporated reserves the right to alter, without notice, specifications, design, price or conditions of supply of any product or service. Customers are solely responsible for obtaining the latest relevant information before placing orders. Applications disclaimer The circuits in this design/application note are offered as design ideas. It is the responsibility of the user to ensure that the circuit is fit for the user’s application and meets with the user’s requirements. No representation or warranty is given and no liability whatsoever is assumed by Diodes Inc. with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Diodes Inc. does not assume any legal responsibility or will not be held legally liable (whether in contract, tort (including negligence), breach of statutory duty, restriction or otherwise) for any damages, loss of profit, business, contract, opportunity or consequential loss in the use of these circuit applications, under any circumstances. Life support Diodes Zetex products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein: A. 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 labelling 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. Reproduction The product specifications contained in this publication are issued to provide outline information only which (unless agreed by the company in writing) may not be used, applied or reproduced for any purpose or form part of any order or contract or be regarded as a representation relating to the products or services concerned. Terms and Conditions All products are sold subjects to Diodes Inc. terms and conditions of sale, and this disclaimer (save in the event of a conflict between the two when the terms of the contract shall prevail) according to region, supplied at the time of order acknowledgement. For the latest information on technology, delivery terms and conditions and prices, please contact your nearest Diodes sales office. Quality of product Diodes Zetex Semiconductors Limited is an ISO 9001 and TS16949 certified semiconductor manufacturer. To ensure quality of service and products we strongly advise the purchase of parts directly from Diodes Incorporated or one of our regionally authorized distributors. For a complete listing of authorized distributors please visit: www.zetex.com or www.diodes.com. Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any parts purchased through unauthorized sales channels. ESD (Electrostatic discharge) Semiconductor devices are susceptible to damage by ESD. Suitable precautions should be taken when handling and transporting devices. The possible damage to devices depends on the circumstances of the handling and transporting, and the nature of the device. The extent of damage can vary from immediate functional or parametric malfunction to degradation of function or performance in use over time. Devices suspected of being affected should be replaced. Green compliance Diodes Zetex Semiconductors is committed to environmental excellence in all aspects of its operations which includes meeting or exceeding regulatory requirements with respect to the use of hazardous substances. Numerous successful programs have been implemented to reduce the use of hazardous substances and/or emissions. All Diodes Zetex components are compliant with the RoHS directive, and through this it is supporting its customers in their compliance with WEEE and ELV directives. Product status key: “Preview” Future device intended for production at some point. Samples may be available “Active” Product status recommended for new designs “Last time buy (LTB)” Device will be discontinued and last time buy period and delivery is in effect “Not recommended for new designs” Device is still in production to support existing designs and production “Obsolete” Production has been discontinued Datasheet status key: “Draft version” This term denotes a very early datasheet version and contains highly provisional information, which may change in any manner without notice. “Provisional version” This term denotes a pre-release datasheet. It provides a clear indication of anticipated performance. However, changes to the test conditions and specifications may occur, at any time and without notice. “Issue” This term denotes an issued datasheet containing finalized specifications. However, changes to specifications may occur, at any time and without notice. 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