ZXSC300 SINGLE OR MULTI CELL LED DRIVER SOLUTION DESCRIPTION the switching transistor. 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 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. 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 FEATURES • 94% efficiency • Minimum operating input voltage 0.8V • Fixed output current • Low saturation voltage switching transistor • SOT23-5 package TYPICAL APPLICATION CIRCUIT VBATT ORDERING INFORMATION L1 100µH U1 Vcc Vdrive Q1 FMMT617 LED1 WHITE LED Isense Gnd ZXSC300 R1 0.33R ISSUE 1 - JUNE 2001 1 DEVICE Package Partmarking ZXSC300E5 SOT23-5 C300 ZXSC300 ABSOLUTE MAXIMUM RATING Supply Voltage Maximum Voltage Other Pins Power Dissipation Operating Temperature Storage Temperature -0.3 to 10V -0.3 to VCC+0.3V 450mW -40 to 85°C -55 to 125°C ELECTRICAL CHARACTERISTICS: Test conditions unless otherwise stated: VCC=1.5V, TAMB=25°C Symbol Parameter Efficiency 1 η Conditions Min Typ 0.8 V CC Recommended supply voltage range V CC(min) Minimum startup and operating voltage IQ Quiescent current 2 I VDRIVE Base drive current 3 I DRIVE =-600µA, V DRIVE =0.7V 0.8 I DRIVE =-600µA, V DRIVE =0.7V, T AMB =-10°C 3 0.9 Max 94 Units % 8 V 0.92 V 0.2 V DRIVE = 0.7V, V ISENSE = 0V mA 1.5 3.6 mA I CC Supply current V DRIVE = 0.7V, V ISENSE = 0V 2 4 mA V VDRIVE(high) High level drive voltage V ISENSE = 0V, I VDRIVE =-0.5mA V CC -0.3 V CC V V VDRIVE(low) Low level drive voltage V ISENSE = 50mV, I VDRIVE = 5mA 0 0.2 V V ISENSE Output current reference voltage 24 mV (threshold) T CVISENSE I SENSE voltage temp co. 2 I ISENSE I SENSE input current 14 19 0.4 V ISENSE = 0V 0 %/°C -30 -65 µA ELECTRICAL CHARACTERISTICS: AC PARAMETERS2 TEST CONDITIONS (Unless otherwise stated) ) VCC=1.5V, TAMB = 0 to 70°C Symbol Parameter T DRV Discharge Pulse Width F OSC Recommended operating frequency 4 Conditions Min 1.2 Typ 1.7 Max Units 3.2 µs 200 kHz 1 Application dependent, see reference designs. These parameters guaranteed by Design 3 Total supply current =IQ + IVDRIVE, see typical characteristics 4 Operating frequency is application circuit dependent. See applications section. 2 ISSUE 1 - JUNE 2001 2 ZXSC300 FMMT617 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 V CE(sat) 8 70 150 14 100 200 mV mV mV I C =0.1A, I B =10mA* I C =1A, I B =10mA* I C =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. Forward Voltage VF Reverse Current IR 50 Reverse Recovery Time t rr 12 ISSUE 1 - JUNE 2001 3 MAX. UNIT CONDITIONS. 400 500 mV mV I F =500mA I F =1A 100 µA V R =30V ns Switched from IF = 500mA to IR = 500mA. Measured at IR=50mA ZXSC300 TYPICAL CHARACTERISTICS 4m Drive Current (A) Quiescent Current (A) 300µ 200µ 100µ 0 1 2 3 4 5 6 Input Voltage (V) 7 3m 2m 1m 0 1 8 3 4 5 6 7 Input Voltage (V) 8 Drive Current v Input Voltage Quiescent Current v Input Voltage 100 30m 25m 20m Efficiency (%) Sense Voltage (V) 2 15m 10m 5m 0 1 2 3 4 5 6 Input Voltage (V) 7 95 90 85 1.0 8 1.5 2.0 2.5 Input Voltage (V) 3.0 3.5 Input Voltage v Efficiency Sense Voltage v Input Voltage ISSUE 1 - JUNE 2001 4 ZXSC300 DEVICE DESCRIPTION With every on pulse the switching transistor is kept on until the voltage across the current-sense resistor exceeds the threshold of the ISENSE 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 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 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. Pin out Diagram Figure 1 ZXSC300 Block Diagram The on chip comparator forces the driver circuit and therefore the external switching transistor off if the voltage at ISENSE exceeds 19mV. This threshold is set by an internal reference circuit and divider. VCC 1 GND 2 3 The Voltage at ISENSE 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. 5 VDRIVE 4 ISENSE Top View Pin Descriptions 1 Pin No. Name V CC Description Supply voltage, generally Alkaline, NiMH or NiCd single cell 2 Gnd Ground 3 N/C Not connected 4 I SENSE Inductor current sense input. Internal threshold voltage set to 19mV. Connect external sense resistor 5 V DRIVE Drive output for external switching transistor. Connect to base of external switching transistor. ISSUE 1 - JUNE 2001 5 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. L1 VBATT D1 100µH ZHCS1000 U1 Q1 Vcc FMMT617 Vdrive C1 Isense 2.2µF LED1 WHITE LED Gnd R1 ZXSC300 0.1R 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 D1 1A ZHCS1000 Zetex Plc 1A Shottky diode, SOT23 R1 100mΩ Generic Various 0805 Size C1 2.2µF Generic Various Low ESR ceramic capacitor L1 100µH DO1608P-104 Coilcraft Surface mount inductor LED1 5600mcd NSPW500BS Nichia White LED ISSUE 1 - JUNE 2001 6 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. 100 L1 VBATT Single LED Load Vcc Vdrive Efficiency (%) 100µH U1 Q1 FMMT617 LED1 WHITE LED Isense Gnd ZXSC300 R1 95 90 0.33R 85 1.0 1.5 2.0 2.5 3.0 Input Voltage (V) Input Voltage v Efficiency Materials 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 0805 Size R1 330mΩ Generic Various L1 100µH DO1608P-104 Coilcraft Surface mount inductor LED1 5600mcd NSPW500BS Nichia White LED ISSUE 1 - JUNE 2001 7 3.5 ZXSC300 APPLICATIONS INFORMATION 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. The following section is a design guide for optimum converter performance. Switching transistor selection The choice of switching transistor has a major impact o n th e c onver t er e f f i c i enc y. For o p t i m u m performance, a bipolar transistor with low VCE(SAT) and high gain is required. Schottky diode selection 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. 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. Peak current definition 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 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. 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. In general, the IPK 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. For the maximum brightness solution a pulsed current is supplied to the LED therefore a Schottky rectifier diode is not required. Once IPK is decided the value of RSENSE can be determined by: RSENSE = Inductor selection VISENSE IPK where VISENSE=19mV 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. ISSUE 1 - JUNE 2001 8 ZXSC300 Output Power Calculation Capacitor selection By making the above assumptions for inductance and peak current the output power can be determined by: POUT = (VOUT- VIN) x (IPK + IMIN) TOFF x (TON + TOFF ) 2 Note: VOUT = output voltage + Schottky rectifier voltage drop where Generally an input capacitor is not required, but a small ceramic capacitor may be added to aid EMC, typically 470nF to 1uF. Demonstration board TOFF ≅ 1.7µs (internally set by ZXSC300) 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. and TON = 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. TOFF (VOUT − VIN) VIN and IMIN = IPK − ( VOUT - VIN ) x TOFF L Operating frequency can be derived by: 1 F= (TON + TOFF ) Layout of Maximum battery life solution Top Copper Drill Holes Bottom Copper Silk Screen ISSUE 1 - JUNE 2001 9 ZXSC300 (Notes) ISSUE 1 - JUNE 2001 10 ZXSC300 Supplier Listing Zetex GERMANY Zetex GmbH Munich ASIA Zetex Asia Hong Kong USA Zetex Inc Long Island NY UK Zetex PLC Chadderton, Oldham (49) 894549490 (852) 2610 0611 (1) 631 543 7100 (44) 161 622 4444 AVX USA (1) 843 448 9411 AVX UK (44) 1252 770000 Coilcraft Inc (1) 847 639 6400 Coilcraft Europe (44) 1236 730595 http://www.zetex.com AVX Asia Singapore (65) 258 2833 AVX http://www.avxcorp.com Coilcraft 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 http://www.nichia.co.jp ISSUE 1 - JUNE 2001 11 Nichia America Corporation Head Office (1) 717 285 2323 San Jose (1) 408 573 0933 ZXSC300 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° 0 10 0 10 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 Streitfeldstraße 19 D-81673 München Germany Telefon: (49) 89 45 49 49 0 Fax: (49) 89 45 49 49 49 Zetex Inc. 47 Mall Drive, Unit 4 Commack NY 11725 USA Telephone: (631) 543-7100 Fax: (631) 864-7630 Zetex (Asia) Ltd. 3701-04 Metroplaza, Tower 1 Hing Fong Road, Kwai Fong, Hong Kong Telephone:(852) 26100 611 Fax: (852) 24250 494 These are supported by agents and distributors in major countries world-wide © Zetex plc 2001 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. 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