ZXSC300 ZETEX | Alldatasheet

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Technical content

DESCRIPTION

The ZXSC300 is a single or multi cell LED driver designed for applications where step-up voltage conversion from very low input voltages is required. These applications mainly operate from single 1.5V or 1.2V battery cells. The circuit generates constant current pulses that are ideal for driving single or multiple LED’s over a wide range of operating voltages. The ZXSC300 is a PFM controller IC that drives an external Zetex switching transistor with a very low saturation resistance. These transistors are the best switching devices available for this type of switching conversion enabling high efficiency conversion with input voltages below 1 volt. The drive output of the ZXSC controller generates a dynamic drive signal for the switching transistor. The circuit can start up under full load and operates down to an input voltage of 0.8 volts. The solution configuration ensures optimum efficiency over a wide range of load currents, several circuit configurations are possible depending on battery life versus brightness considerations. The ZXSC300 is offered in the SOT23-5 package which, when combined with a SOT23 switching transistor, generates a high efficiency small size circuit solution. The IC and discrete combination offers the ultimate cost vs performance solution for single cell LED driving applications. SINGLE OR MULTI CELL LED DRIVER SOLUTION

FEATURES

  • 94% efficiency
  • Minimum operating input voltage 0.8V
  • Fixed output current
  • Low saturation voltage switching transistor
  • SOT23-5 package FMMT617 0.33R 100µH VBATT LED1 WHITE LED Vcc Gnd Isense Vdrive ZXSC300 TYPICAL APPLICATION CIRCUIT ISSUE 1 - JUNE 2001

ORDERING INFORMATION

Supply Voltage -0.3 to 10V Maximum Voltage Other Pins -0.3 to V CC+0.3V Power Dissipation 450mW Operating Temperature -40 to 85 °C Storage Temperature -55 to 125 °C ELECTRICAL CHARACTERISTICS: Test conditions unless otherwise stated: VCC=1.5V, TAMB=25°C Symbol Parameter Conditions Min Typ Max Units η Efficiency 1 94 % VCC Recommended supply voltage range 0.8 8 V V CC(min) Minimum startup and operating voltage I DRIVE =-600µA, V DRIVE =0.7V IDRIVE =-600µA, V DRIVE =0.7V, TAMB =-10°C 3 0.8 0.9 0.92 V IQ Quiescent current 2 0.2 mA IVDRIVE Base drive current V DRIVE = 0.7V, V ISENSE = 0V 1.5 3.6 mA ICC Supply current 3 VDRIVE = 0.7V, V ISENSE =0 V 2 4 m A VVDRIVE(high) High level drive voltage VISENSE = 0V, I VDRIVE =-0.5mA V CC-0.3 V CC V VVDRIVE(low) Low level drive voltage VISENSE = 50mV, I VDRIVE = 5mA 0 0.2 V VISENSE (threshold) Output current reference voltage 14 19 24 mV TCVISENSE ISENSE voltage temp co. 2 0.4 %/°C IISENSE ISENSE input current V ISENSE = 0V 0 -30 -65 µA ELECTRICAL CHARACTERISTICS: AC PARAMETERS2 TEST CONDITIONS (Unless otherwise stated) ) VCC=1.5V, TAMB = 0 to 70°C Symbol Parameter Conditions Min Typ Max Units TDRV Discharge Pulse Width 1.2 1.7 3.2 µs FOSC Recommended operating frequency 4 200 kHz 1 Application dependent, see reference designs.

2 These parameters guaranteed by Design

3 Total supply current =IQ + IVDRIVE, see typical characteristics

4 Operating frequency is application circuit dependent. See applications section.

For the circuits described in the applications section, Zetex FMMT617 is the recommended pass transistor. The following indicates outline data for the transistor, more detailed information can be found in the Zetex surface mount data book or at www.zetex.com ELECTRICAL CHARACTERISTICS (at TA = 25°C unless otherwise stated). PARAMETER SYMBOL MIN. TYP. MAX. UNIT CONDITIONS. Collector-Emitter Saturation Voltage VCE(sat) 8 150 100 200 mV mV mV I C=0.1A, I B=10mA* IC=1A, I B=10mA* IC=3A, I B=40mA* Collector-Emitter Breakdown Voltage V(BR)CEO 15 18 V I C=10mA* *Measured under pulsed conditions. Pulse width=300µs. Duty cycle ≤ 2% ZHCS1000 For the circuits described in the applications section Zetex ZHCS1000 is the recommended Schottky diode. The following indicates outline data for the diode, more detailed information is available at www.zetex.com ELECTRICAL CHARACTERISTICS (at Tamb = 25°C unless otherwise stated). PARAMETER SYMBOL MIN. TYP. MAX. UNIT CONDITIONS. Forward Voltage V F 400 500 mV mV IF=500mA IF=1A Reverse Current I R 50 100 µ A VR=30V Reverse Recovery Time trr 12 ns Switched from I F = 500mA to IR = 500mA. Measured at IR=50mA

100µ 200µ 300µ 123456780 123456780 10m 15m 20m 25m 30m 100 Drive Current v Input Voltage Quiescent Current (A) Input Voltage (V) Input Voltage v Efficiency Drive Current (A) Input Voltage (V) Sense Voltage v Input Voltage Sense Voltage (V) Input Voltage (V) Quiescent Current v Input Voltage Efficiency (%) Input Voltage (V)

The ZXSC300 is PFM, controller IC which, when combined with a high performance external transistor, enables the production of a high efficiency boost converter for use in single cell LED driving applications. A block diagram is shown for the ZXSC300 in Figure 1. The on chip comparator forces the driver circuit and therefore the external switching transistor off if the voltage at I SENSE exceeds 19mV. This threshold is set by an internal reference circuit and divider. The Voltage at I SENSE is taken from a current sense resistor connected in series with the emitter of the switching transistor. A monostable following the output of the comparator forces the turn-off time of the output stage to be typically 1.7µs. This ensures that there is sufficient time to discharge the inductor coil before the next on period. With every on pulse the switching transistor is kept on until the voltage across the current-sense resistor exceeds the threshold of the I SENSE input. The on-pulse length, and therefore the switching frequency, is determined by the programmed peak current, the input voltage and the input to output voltage differential. See applications section for details. The Driver circuit supplies the external switching transistor with a fixed drive current. To maximise efficiency the external transistor switched quickly, typically being forced off within 30ns. Figure 1 ZXSC300 Block Diagram Pin Descriptions Pin No. Name Description 1V CC Supply voltage, generally Alkaline, NiMH or NiCd single cell

2 Gnd Ground

3 N/C Not connected

SENSE Inductor current sense input. Internal threshold voltage set to 19mV. Connect external sense resistor 5V DRIVE Drive output for external switching transistor. Connect to base of external switching transistor. VCC VDRIVE GND Top View ISENSE Pin out Diagram

Ref Value Part Number Manufacture Comments U1 N/A ZXSC300E5 Zetex Plc Single cell converter, SOT23-5 Q1 N/A FMMT617 Zetex Plc Low V CE(sat) NPN, SOT23 D1 1A ZHCS1000 Zetex Plc 1A Shottky diode, SOT23 R1 100m Ω Generic Various 0805 Size C1 2.2 µ F Generic Various Low ESR ceramic capacitor L1 100µH DO1608P-104 Coilcraft Surface mount inductor LED1 5600mcd NSPW500BS Nichia White LED FMMT617 0.1R 100µH VBATT LED1 WHITE LED ZHCS1000 2.2µF Vcc Gnd Isense Vdrive ZXSC300 REFERENCE DESIGNS Two typical LED driving applications are shown. Firstly a maximum brightness solution and secondly an optimised battery life solution. Maximum brightness solution This circuit provides a constant current output to the LED by rectifying the switching pulses. This ensures maximum LED brightness. Material List

Ref Value Part Number Manufacture Comments U1 N/A ZXSC300E5 Zetex Plc Single cell converter, SOT23-5 Q1 N/A FMMT617 Zetex Plc Low V CE(SAT) NPN, SOT23 R1 330m Ω Generic Various 0805 Size L1 100 µ H DO1608P-104 Coilcraft Surface mount inductor LED1 5600mcd NSPW500BS Nichia White LED 100 Input Voltage v Efficiency Single LED Load Efficiency (%) Input Voltage (V) FMMT617 0.33R 100µH VBATT LED1 WHITE LED Vcc Gnd Isense Vdrive ZXSC300 Maximum battery life solution To ensure optimum efficiency, and therefore maximum battery life, the LED is supplied with a pulsed current. Maximum efficiency is ensured with the removal of rectifier losses experienced in the maximum brightness solution. Materials list

The following section is a design guide for optimum converter performance. Switching transistor selection The choice of switching transistor has a major impact on the converter efficiency. For optimum performance, a bipolar transistor with low V CE(SAT) and high gain is required. The Zetex FMMT617 is an ideal choice of transistor, having a low saturation voltage. A data sheet for the FMMT617 is available on Zetex web site or through your local Zetex sales office. Outline information is included in the characteristics section of this data sheet. Schottky diode selection For the maximum battery life solution a Schottky rectifier diode is required. As with the switching transistor the Schottky rectifier diode has a major impact on the converter efficiency. A Schottky diode with a low forward voltage and fast recovery time should be used for this application. The diode should be selected so that the maximum forward current is greater or equal to the maximum peak current in the inductor, and the maximum reverse voltage is greater or equal to the output voltage. The Zetex ZHCS1000 meets these needs. Datasheets for the ZHCS Series are available on Zetex web site or through your local Zetex sales office. Outline information is included in the characteristics section of this data sheet. For the maximum brightness solution a pulsed current is supplied to the LED therefore a Schottky rectifier diode is not required. Inductor selection The inductor value must be chosen to satisfy performance, cost and size requirements of the overall solution. For the reference designs we recommend an inductor value of 100uH with a core saturation current rating greater than the converter peak current value and low series resistance. Inductor selection has a significant impact on the converter performance. For applications where efficiency is critical, an inductor with a series resistance of 500mΩ or less should be used. Peak current definition The peak current rating is a design parameter whose value is dependent upon the overall application. For the high brightness reference designs, a peak current of was chosen to ensure that the converter could provide the required output power to the LED. In general, the I PK value must be chosen to ensure that the switching transistor, Q1, is in full saturation with maximum output power conditions, assuming worse-case input voltage and transistor gain under all operating temperature extremes. Once I PK is decided the value of R SENSE can be determined by: R V ISENSE ISENSE PK where VISENSE=19mV

By making the above assumptions for inductance and peak current the output power can be determined by: P (V V x I I OUT OUT- IN PK MIN = +)( ) 2 x T TT OFF ON OFF() + Note: V OUT = output voltage + Schottky rectifier voltage drop where TOFF ≅ 1.7µs (internally set by ZXSC300) and T TV V VON OFF OUT IN IN = −() and II (V - V xT LMIN PK OUT IN OFF =− ) Operating frequency can be derived by: F TTON OFF = + Capacitor selection For pulsed operation, as in the maximum battery life solution, no capacitors are required at the output to the LED. For rectified operation, as in the maximum brightness solution, a small value ceramic capacitor is required, typically 2.2uF. Generally an input capacitor is not required, but a small ceramic capacitor may be added to aid EMC, typically 470nF to 1uF. Demonstration board A demonstration board for the Maximum battery life solution, is available upon request. These can be obtained through your local Zetex office or through Zetex web pages. For all reference designs Gerber files and bill of materials can be supplied. Layout of Maximum battery life solution Top Copper Drill Holes Bottom Copper Silk Screen

(Notes)

Chadderton, Oldham (49) 894549490 (852) 2610 0611 (1) 631 543 7100 (44) 161 622 4444 http://www.zetex.com AVX AVX Asia Singapore (65) 258 2833 AVX USA (1) 843 448 9411 AVX UK (44) 1252 770000 http://www.avxcorp.com Coilcraft Coilcraft Inc (1) 847 639 6400 Coilcraft Europe (44) 1236 730595 http://www.coilcraft.com Nichia Corporation Nichia Europe B.V. Amsterdam The Netherlands (31) 20 5060900 Nichia Corporation Tokyo Sales Office Tokyo, Japan (81) 3 3456 3784 Nichia America Corporation Head Office (1) 717 285 2323 San Jose (1) 408 573 0933 http://www.nichia.co.jp Supplier Listing

Zetex plc. Fields New Road, Chadderton, Oldham, OL9-8NP, United Kingdom. Telephone: (44)161 622 4422 (Sales), (44)161 622 4444 (General Enquiries) Fax: (44)161 622 4420 Zetex GmbH Zetex Inc. Zetex (Asia) Ltd. These are supported by Streitfeldstraße 19 47 Mall Drive, Unit 4 3701-04 Metroplaza, Tower 1 agents and distributors in D-81673 München Commack NY 11725 Hing Fong Road, major countries world-wide Germany USA Kwai Fong, Hong Kong © Zetex plc 2001 Telefon: (49) 89 45 49 49 0 Telephone: (631) 543-7100 Telephone:(852) 26100 611 Fax: (49) 89 45 49 49 49 Fax: (631) 864-7630 Fax: (852) 24250 494 www.zetex.com This publication is 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. The Company reserves the right to alter without notice the specification, design, price or conditions of supply of any product or service. Publication Ref. SCZXSC300DS PACKAGE DIMENSIONS SOT23-5 DIM Millimetres Inches MIN MAX MIN MAX A 0.90 1.45 0.035 0.057 A1 0.00 0.15 0.00 0.006 A2 0.90 1.3 0.035 0.051 b 0.35 0.50 0.014 0.020 C 0.09 0.20 0.0035 0.008 D 2.80 3.00 0.110 0.118 E 2.60 3.00 0.102 0.118 E1 1.50 1.75 0.059 0.069 e 0.95 REF 0.037 REF e1 1.90 REF 0.075 REF L 0.10 0.60 0.004 0.024 a° 01 0 01 0