ZXLD381 ZETEX | Alldatasheet
Document overview
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Technical content
Features
- 85% Efficiency User adjustable output current Single cell operation (0.9V minimum) L o w s a t u r a t i o n voltage switching transistor SOT23-3 package Available also in Die form Simple Application circuit
Applications
LED flashlights and torches LED backlights White LED driver LED ZXLD381 GN D VOUT VCC VIN
Issue 1 - April 2008 2 www.zetex.com © Zetex Semiconductors plc 2008 Absolute maximum ratings Supply Voltage (VCC) -0.6V to 10V Output Voltage (VOUT) -0.6V to 20V Supply Current 20mA Output Switch Current 800mA Power Dissipation SOT23-3 450mW Power Dissipation Die 1W Operating Temperature Range 0°C to +85°C Storage Temperature Range -55°C to +150°C
Electrical Characteristics
Measured at TAMB = 25°C, L = 4.7μH and VCC = 1.5V unless otherwise specified. Parameter Conditions Limits Units Min Typ Max Supply Voltage Operating Range L = 10μH0 . 9 2 . 2 V Minimum Supply Start-up Voltage L = 10μH0 . 8 0 . 9 V Switch Current At turn-off 250 320 400 mA Switch Saturation Voltage IOUT = 200mA 100 300 mV Switch Leakage Current VOUT = 20V 40 70 120 μA Mean LED Current V LED = 3.5V 40 55 70 mA Efficiency V LED = 3.5V 85 % Operating Frequency VLED = 3.5V 350 kHz Discharge Pulse Width 0.7 1.5 2.5 μs
Issue 1 - April 2008 3 www.zetex.com © Zetex Semiconductors plc 2008 Typical Characteristics Channel-1 (Upper): ILED @ 100mA/cm Channel-2 (Lower): VOUT @ 1V/cm Timebase: 500ns/cm ZXLD381 Operating Waveforms for L = 4.7uH, VCC = 1.5V ZXLD 381 IOUT (A VER AG E) vs VCC fo r L = 2.2uH to 47uH 10 0 VCC (V ) IOUT (mA) 2.2uH 3.3uH 4.7uH 6.8uH 10uH 15uH 22uH 47uH ZXLD381 Efficiency vs VCC fo r L = 2.2uH to 47uH 100 VCC (V) E fficiency (%) 2. 2 uH 3. 3 uH 4. 7 uH 6. 8 uH 1 0uH 1 5uH 2 2uH 4 7uH ZXLD381 IIN vs VCC for L = 2.2uH to 47uH 10 0 15 0 20 0 25 0 30 0 35 0 V CC (V ) IIN (mA) 2.2uH 3.3uH 4.7uH 6.8uH 10uH 15uH 22uH 47uH ZXLD381 fOSC vs VCC fo r L = 4 .7uH 10 0 15 0 20 0 25 0 30 0 35 0 40 0 45 0 V CC (V) fOSC (kHz)
Issue 1 - April 2008 4 www.zetex.com © Zetex Semiconductors plc 2008 Device Description The ZXLD381 is a simple PFM, DC-DC controlle r 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. Figure 1 ZXLD381 Block Diagram 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 forc es the supply voltage across th e 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 pul se 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 V OUT 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 V OUT 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 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 fo r 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 ZXLD 381 GND VOUT VCC 1.5 V LED CoffCon Pulse Cont rol Rsense
Issue 1 - April 2008 5 www.zetex.com © Zetex Semiconductors plc 2008 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 V CC. (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. Application Examples Standard Operating Mode Note: VLED = 3.5V Low Ripple LED Current Mode Note: VLED = 3.5V, D1 = ZHCS1000, C1 = 1μF (low ESR) LI LED(peak) I LED(avg) (uH) (mA) (mA) 47 35 6.5 22 80 15 15 120 20 10 190 30 6.8 260 45 4.7 380 55 3.3 510 67 2.2 640 76 LI LED (uH) (mA) 47 6 22 13.5 15 18 10 27 6.8 41 4.7 50 3.3 61 2.2 69 1.5V LED ZXLD381 GND VOUT VCC 1.5V LED ZXLD381 GND VOUT VCC
Issue 1 - April 2008 6 www.zetex.com © Zetex Semiconductors plc 2008 PIN Descriptions Pinout diagram
Ordering Information
Pin No. Name Description 1G ND Ground 2V OUT Switch output external inductor/LED 3V CC Supply voltage, generally Alkaline, NiMH or NiCd single cell Device Package Part Mark ZXLD381FHTA SOT23 381 VCC VOUT GND Top view
Issue 1 - April 2008 7 www.zetex.com © Zetex Semiconductors plc 2008 Packaging Information- SOT23 Note: controlling dimensions are in millimetres. Approximate dimensions are given in inches. Dim. Millimeters Inches Dim. Millimeters Inches A - 1.12 - 0.044 e1 1.90 NOM 0.075 NOM e0 . 9 5 N O M0 . 0 3 7 N O M ----- E e L D A c E1L1 b 3 leads
Issue 1 - April 2008 8 www.zetex.com © Zetex Semiconductors plc 2008 Zetex sales offices Europe Zetex GmbH Kustermann-park Balanstraße 59 D-81541 München Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 europe.sales@zetex.com Americas Zetex Inc
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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 ha s been discontinued Datasheet status key: “Draft version” This term denotes a very early datasheet ver sion 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 cont aining finalized specifications. However, changes to specifications may occur, at any time and without notice.