A Product Line of Diodes Incorporated ZXLD383 SINGLE OR MULTI CELL LED DRIVER SOLUTION 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. 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. Features • • • • • • • Pin Assignments 85% Efficiency User adjustable output current Single cell operation Low saturation voltage TSOT23-3 package Available also in die form Simple application circuit TSOT23-3 ENA 1 VCC 4 VOUT GND 2 NC 3 (Top View) Application • • • • • • 5 Garden lights Door/pathway illumination LED flashlight and torches LED backlights White LED driver Gated boost supply generator Typical Application Circuit ZXLD383 Document number: DS32189 Rev. 3 - 2 1 of 10 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD383 Block Diagram VC C L1 Z XLD 383 D iode Array VO U T EN A Puls e C ontrol N IMH 1.2V LED Dch C on Coff R s ens e GN D Fig 1. ZXLD383 Block Diagram Pin Description Pin No. 1 2 3 Name ENA GND NC Description Enable / Photodiode array battery charge input Ground Not connected (internally open circuit) 4 VOUT Switch output external inductor/LED 5 VCC Supply voltage, generally Alkaline, NiMH or NiCd single cell ZXLD383 Document number: DS32189 Rev. 3 - 2 2 of 10 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD383 Absolute Maximum Ratings Rating Unit Supply Voltage (VCC) Parameter -0.6 to 6 V Output Voltage (VOUT) -0.6 to 20 V Enable Voltage (VENA) Supply Current Output Switch Current Power Dissipation (TSOT23-3) Power Dissipation Die Operating Temperature Range Storage Temperature Range -1 to 3.5 V 20 800 450 1 -20 to 85 -55 to 150 mA mA mW W °C °C Electrical Characteristics Measured at TAMB = 25°C, L = 6.8µH, IENA = 0 and VCC = 1.5V unless otherwise specified. Parameter Conditions Supply Voltage Operating Range Minimum Supply Start-up Voltage Supply Current Quiescent L = 10μH L = 10μH Supply Current Shutdown VENA = VCC – 0.8V Supply Current Under-Voltage VCC = 0.6V Switch Current At turn-off Min 0.9 2 250 Switch Saturation Voltage IOUT = 200mA Switch Leakage Current VOUT = 20V, VENA = 0V Mean LED Current VLED = 3.5V Efficiency VLED = 3.5V Operating Frequency VLED = 3.5V 40 Limits Typ. Units 0.8 4 Max 3.3 0.9 8 17 30 µA 20 µA V V mA 320 400 mA 100 300 mV 10 µA 65 mA 50 85 % 330 kHz Discharge Pulse Width 0.7 1.5 2.5 µs Enable Input Threshold VCC - 0.6 -11 VCC - 0.2 -20 µA -90 -250 mV Enable Input Current VENA = 0.2V VCC - 0.8 0 Enable Input Voltage IENA = -20mA 0 ZXLD383 Document number: DS32189 Rev. 3 - 2 3 of 10 www.diodes.com V May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated 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. 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 channeled 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 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. ZXLD383 Document number: DS32189 Rev. 3 - 2 4 of 10 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD383 Typical Characteristics 90 100 22µH 10µH 80 90 4.7µH 80 70 6.8µH 70 Efficiency (%) IOUT (mA) 60 50 10µH 40 60 50 40 6.8µH 30 30 22µH 20 20 4.7µH 47µH 10 0 47µH 10 0.8 1 1.2 1.4 1.6 V CC (V) IO UT(AVERAG E) vs. V CC 1.8 0 2 0.8 1 1.2 1.4 1.6 1.8 V CC (V) Efficiency vs. V CC for L = 2.2µH to 47µH 2 500 250 450 350 4.7µH 6.8µH 150 IIN (mA) IIN (mA) 4.7µH 400 200 6.8µH 300 250 10µH 200 100 10µH 150 22µH 50 22µH 100 47µH 50 47µH 0 0.8 Notes: 0 1 1.2 1.4 1.6 V CC (V) I IN vs. VC C 1.8 2 0.8 1 1.2 1.4 1.6 V CC (V) Peak IIN vs. VCC 1.8 2 VLED = 3.5V for all graphs ZXLD383 Document number: DS32189 Rev. 3 - 2 5 of 10 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD383 Typical Characteristics (Cont.) 450 400 0.8V 350 V ENA (mA) 300 1.0V 250 1.2V 200 150 100 50 1.4V 0 0 Notes: 10 20 30 40 IV ENA (mA) V(ENA) vs. IENA For VI N = 0.8, 1.2, 1.4V 50 Channel-1 (Upper): I LED @ 100mA/cm Channel-2 (Lower): VO UT @ 1V/cm Timebase: 500ns/cm Operating Waveform for L = 6.8µH, V CC = 1.5V VLED = 3.5V for all graphs ZXLD383 Document number: DS32189 Rev. 3 - 2 6 of 10 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD383 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 5 1 VC C I L E D (peak ) I L E D (avg) (uH ) (m A ) (m A ) L1 2 4 3 VOU T 1.5V LED Notes: L 47 45 8.5 22 100 17.3 10 210 34 6.8 330 50 4.7 415 63 VLED = 3.5V 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 XL D 3 8 3 EN A GN D 1 5 VC C L1 2 D1 NC 3 4 VOU T C1 1.5V LED L IL E D (uH ) (m A ) 47 7.5 22 15.5 10 31 6.8 46 4.7 58 Notes: VLED = 3.5V, D1 = ZHCS1000, C1 = 1µF (low ESR) ZXLD383 Document number: DS32189 Rev. 3 - 2 7 of 10 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD383 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. LED Z XLD 383 3V EN A 1 GN D 5 VC C L1 2 NC 4 3 L IL E D (uH ) (m A ) 47 5.5 22 10.3 10 23.2 6.8 36.7 4.7 46.2 VO U T Notes: VLED = 3.5V 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 LED Z XLD 383 3V EN A GN D 1 5 VC C L1 2 L IL E D (uH ) (m A ) 47 5 22 9 .7 10 2 1.7 6.8 34 4.7 43 D1 NC 3 4 VO U T Note: VLED =3.5V, D1=ZHCS1000, C1 = 1uF (low ESR) ZXLD383 Document number: DS32189 Rev. 3 - 2 8 of 10 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD383 Ordering Information Part Number Package Part Mark ZXLD383ET5TA TSOT23-5 383 Tape Width (mm) 8 Quantity (per reel) 3000 Package Outline Dimensions Millimeters Inches Dim. Millimeters 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 ZXLD383 Document number: DS32189 Rev. 3 - 2 Min. 0.10 Q 9 of 10 www.diodes.com Max. 0.60 0.25 BSC 4 12 Min. 0.0039 Max. 0.0236 0.010 BSC 4 12 May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD383 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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