A Product Line of Diodes Incorporated ZXLD381 SINGLE OR MULTI CELL LED DRIVER SOLUTION Summary The ZXLD381 is a single cell LED driver designed for applications where step-up voltage conversion from a very low input voltage is required. These applications mainly operate from 1.5V or 1.2V cells. The IC generates constant current pulses that are ideal for driving single or multiple LEDs over a wide range of operating voltages. The ZXLD381 uses a PFM control technique to drive an internal switching transistor which a low saturation resistance. This ensures high efficiency, even for input voltages as low as 1V. The IC can start up under full load and operates down to an input voltage of only 0.9V. The ZXLD381 is offered in the space saving SOT23 package or in die form, offering an excellent cost vs performance solution for single cell LED driving applications. Features • • • • • • • Pin Assignments SOT23-3 85% Efficiency User adjustable output current Single cell operation (0.9V minimum) Low saturation voltage switching transistor SOT23-3 package Available also in Die form Simple Application circuit (Top View) Application • • • LED flashlights and torches LED backlights White LED driver Typical Application Circuit VIN L1 VCC VOUT LED GND ZXLD381 ZXLD381 Document number: DS32188 Rev. 3 - 2 1 of 9 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD381 Block Diagram VCC L1 ZXLD381 VOUT Pulse Control LED 1.5V Con Coff Rsense GND Fig 1. ZXLD381 Block Diagram Pin Description Pin No. 1 Name GND Ground 2 VOUT Switch output external inductor/LED 3 VCC Supply voltage, generally Alkaline, NiMH or NiCd single cell ZXLD381 Document number: DS32188 Rev. 3 - 2 Description 2 of 9 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD381 Absolute Maximum Ratings Rating Unit Supply Voltage (VCC) Parameter -0.6 to 10 V Output Voltage (VOUT) Supply Current Output Switch Current Power Dissipation SOT23-3 Power Dissipation Die Operating Temperature Range Storage Temperature Range -0.6 to 20 V 20 800 450 1 0 to 85 -55 to 150 mA mA mW W °C °C Electrical Characteristics Measured at TAMB = 25°C, L = 4.7µH and VCC = 1.5V unless otherwise specified. Parameter Conditions Supply Voltage Operating Range Minimum Supply Start-up Voltage Switch Current L = 10μH L = 10μH At turn-off Switch Saturation Voltage IOUT = 200mA Min 0.9 250 Limits Typ. 0.8 320 Max 2.2 0.9 400 Units V V mA 100 300 mV VOUT = 20V 40 70 120 µA Mean LED Current VLED = 3.5V 40 55 70 mA Efficiency VLED = 3.5V 85 % Operating Frequency VLED = 3.5V 350 kHz Switch Leakage Current Discharge Pulse Width ZXLD381 Document number: DS32188 Rev. 3 - 2 0.7 3 of 9 www.diodes.com 1.5 2.5 µs May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD381 Device Description The ZXLD381 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. A block diagram is shown for the ZXLD381 in Fig 1. When power is applied, 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, which initiates the next energy charge cycle. Except for low level losses, all the energy stored in the inductor during a charge cycle will be 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 ZXLD381 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 ZXLD381 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 0.8V 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. ZXLD381 Document number: DS32188 Rev. 3 - 2 4 of 9 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD381 Typical Characteristics 100 100 22µH 47µH 90 2.2µH 90 80 80 15µH 70 10µH 3.3µH 60 Efficiency (%) IO UT (mA) 70 4.7µH 50 6.8µH 40 10µH 50 6.8µH 40 30 30 15µH 20 60 20 4.7µH 3.3µH 22µH 10 10 47µH 2.2µH 0 0 0.8 1 1.4 1.6 1.8 V CC (V) vs. V CC for L = 2.2µH to 47µH 1.2 IO UT(AVERA GE) 0.8 2 1 1.2 1.4 1.6 1.8 V CC (V) Efficiency vs. V CC for L = 2.2µH to 47µH 2 350 300 2.2µH 250 IIN (mA) 3.3µH 200 4.7µH 150 100 6.8µH 10µH 15µH 22µH 50 47µH 0 Notes: 0.8 1 1.2 1.4 1.6 1.8 V CC (V) IIN vs. V CC for L = 2.2µH to 47µH 2 Channel-1 (Upper): I LED @ 100mA/cm Channel-2 (Lower): VOUT @ 1V/cm Timebase: 500ns/cm Operating Waveforms for L = 4.7µH, V CC = 1.5V VLED = 3.5V for all graphs ZXLD381 Document number: DS32188 Rev. 3 - 2 5 of 9 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD381 Typical Characteristics (Cont.) 450 400 350 f OSC (kHz) 300 250 200 150 100 50 0 Notes: 0.8 1 1.2 1.4 1.6 1.8 V CC (V) f OSC vs. V CC for L = 47µH 2 VLED = 3.5V for all graphs ZXLD381 Document number: DS32188 Rev. 3 - 2 6 of 9 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD381 Application Examples Standard Operating Mode Notes: VLED = 3.5V Low Ripple LED Current Mode Notes: VLED = 3.5V, D1 = ZHCS1000, C1 = 1F (low ESR) ZXLD381 Document number: DS32188 Rev. 3 - 2 7 of 9 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD381 Ordering Information Part Number Package Part Mark ZXLD381FHTA SOT23 381 Tape Width (mm) 8 Quantity (per reel) 3000 Package Outline Dimensions E e e1 b 3 leads L1 D E1 A L A1 c Millimeters Inches Dim. Millimeters Inches Dim. Min. Max. Min. Max. A - 1.12 - 0.044 e1 A1 0.01 0.10 0.0004 0.004 E 2.10 2.64 0.083 0.104 b 0.30 0.50 0.012 0.020 E1 1.20 1.40 0.047 0.055 c 0.085 0.20 0.003 0.008 L 0.25 0.60 0.0098 0.0236 D 2.80 3.04 0.110 0.120 L1 0.45 0.62 0.018 0.024 - - - - - e 0.95 NOM ZXLD381 Document number: DS32188 Rev. 3 - 2 0.037 NOM Min. Max. 1.90 NOM 8 of 9 www.diodes.com Min. Max. 0.075 NOM May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD381 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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