ZXSC310EV6 EVALUATION BOARD USER GUIDE ZXSC310 DESCRIPTION The ZXSC310 is a single or multi-cell LED driver designed for LCD backlighting applications. The input voltage range of the device is between 0.8V and 8V. This means that the ZXSC310 is compatible with single NiMH, NiCd or Alkaline cells, as well as multi-cell or Li-Ion batteries. The device features a shutdown control, resulting in a standby current less than 5µA, and an output capable of driving serial or parallel LEDs. The circuit generates a constant power output, which is ideal for driving single or multiple LEDs over a wide range of operating voltages. These features make the device ideal for driving LEDs in LCD backlight applications, for example, in Digital Still cameras and PDAs. The ZXSC310 is a PFM DC-DC controller IC that drives an external Zetex switching transistor with a very low saturation resistance. Such transistors are excellent for this type of conversion, enabling high efficiency conversion with low input voltages. The drive output of the ZXSC310 LED driver generates a dynamic drive signal for the switching transistor. The ZXSC310 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 costversus-performance solution for LED backlight applications. FEATURES TYPICAL APPLICATIONS • • • • • • • • • • • • • • • 94% efficiency Minimum operating input voltage 0.8V Maximum operating input voltage 8V Standby current less than 5µA Programmable output current Series or parallel LED configuration Low saturation voltage switching transistor SOT23-5 package LCD backlights: Digital still camera PDA Mobile phone LED flashlights and torches White LED driving Multiple LED driving ORDERING INFORMATION EVALBOARD ORDER NUMBER ZXSC310EV6 DEVICE ORDER NUMBER ZXSC310E5TA Please note: Evaluation boards are subject to availability and qualified sales leads. Figure 1: ZXSC310EV6 evaluation board Issue 1 – February 2009 © Diodes Incorporated, 2009 www.zetex.com www.diodes.com ZXSC310EV6 REFERENCE DESIGN Schematic Diagram Vbatt Vout L1 10u D1 ZHSC1000 U1 1 Vcc 3 Q1 ZXTN25012 5 Drive En Batt 2 GND 4 Sense C2 1u D2 K2 Vs ZXSC310: R6 20mR Figure 2: Conceptual Schematic for the evaluation board ZXSC310EV6 (The LED is not fitted on the board) The ZXSC310EV6, Figure 1, is an evaluation board for the ZXSC310 boost LED driver. It is configured as in Fig. 2, to drive approximately 200mA into either a single LED, or an external choice of LEDs, from a single 1.5V battery. The operating voltage is nominally 1.5 volts, but the circuit will operate from 0.8volts up to 8 volts. The 10uH inductor used in the circuit has been chosen as being the optimum value for this voltage range. Power should be applied across the +VE and -VE pins, or, alternatively, a 1.5v ‘AA’ size battery can be inserted in the clips provided. The nominal input current for the evaluation board is 600mA, and the operating frequency will be about 250kHz Note: The evaluation board does not have reverse battery protection. WARNING: Exposed battery connections exist on the front and back of the board. Do not cause the batteries to short-circuit by placing it on a conductive surface or allowing other conductive materials to come into contact with it. SL 2 3 P2 boost option 1 2 15u 1 2 SL U1 P4 Bat1 Batt D1 L1 1 TP C1 1u 1 2 1 SL 3 2 Vcc R1 R2 1 Vbatt SL Drive 5 3 10k@25C En GND Q1 ZXTN25012EFH Sense 4 SK1 C3 1u 2 TP3 P3 1 2 1 2 P1 D2 Rebel R4 1 2 3 4 5 6 12 11 10 9 8 7 ZD1 BZX84-C10 100R C2 1u ZXSC310: R5 20mR FUTURE 6X2 TP4 TP TP2 TP1 GND The zener is to protect the transistor in case the led is not fitted. Figure 3: Actual schematic for ZXSC310 EV6 (The LED is not fitted on the board) Issue 1 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 2 ZXSC310EV6 Differences between the Actual and Conceptual Schematics The actual board has several different configurations, as in the schematic Fig. 3. Some of these are not appropriate for this application. R4 is not needed in this application, so a low (or zero) value resistor fitted. For operation as described, solder links P1 and P4 should be shorted and P1 and P2 left open. The LED is not fitted. A LED suitable for the actual application can be fitted on an external PCB via SK1. The zener diode is fitted to protect Q1 against high voltages that would be produced by the circuit of there was an open circuit load. It is not needed for applications where the LED is permanently connected. Design Procedure The objective of this evaluation board is to drive the LED with the maximum current, subject to a reasonable efficiency and component cost. Fundamentally for this type of circuit the limiting factor is the peak current through the inductor. Using the ZXTN25012 with the ZXSC310 at 1.0V to 1.5V the highest design current is about 1A. The threshold Voltage on the Isense pin is given as 19mV so a 19mR resistor could be used. The next highest preferred value is 20mR and the dissipation is only 20mW, so an 0805 package is adequate. The ZXTN25012 is optimized for this type of application as it has an excellent combination of Vcesat and gain at 1A. If a different type of transistor is used, the value of the sense resistor may have to be increased, causing a reduction in output current. The choice of inductor is a compromise between size and price. The small 10uH is a good compromise here: a larger inductor value in the same case would have a higher series resistance and hence higher losses. The value is not critical: a higher value could be used with little change in performance. If the inductor is too small, not only is the power output reduced, but the circuit could enter discontinuous mode, which is undesirable for e.m.c. and efficiency reasons. The Schottky diode should have low forward voltage at 1A: the ZHSC1000 comes in a SOT23 package and has a Vf of about 400mV at 1A. The output capacitor could be regarded as unnecessary, as the flicker that results from it’s omission is not visible, but it helps with respect to e.m.c. In this design the ‘Enable’ pin is tied to the Vcc pin (via solder link P4), as it’s functionality is not used. If no load is placed on the circuit, the output voltage continues to rise to an unacceptable level, so ZD1 is included to limit the voltage to approximately 10volts. For other reference designs or further applications information, please refer to the ZXSC310 datasheet, Application Notes and Design Notes at www.zetex.com. Issue 1 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 3 ZXSC310EV6 Figure 4: Component layout ZXLD1360EV6 Component list Designator U1 ZD1 Q1 D1 Value ZXSC310E5 BZX84C10 350mW ZXTN25012EFH ZHCS1000 Footprint SOT23-5 SOT23A SOT23 SOT23 C1, C2 1uF, 10V 0805 C3 1uF, 16V 0805 L1 R1 R2 R4 R5 SK1 SW1 Bat1 10uH 1.5A 10k 10k 100R 20mR N/A Slide switch, SPDT Batt holder NPIS73100 0805 0805 0805 0805 DIL Name +Ve -Ve TP1 TP2 LED+ LEDSK1 Part No ZXSC310E5 ZXTN25012EFH ZHCS1000 C0805C105K8RAC GRM21BR71A105KA01L NMC0805X7R105K10 C0805C105K4RAC GRM21BR71C105KA01L NMC0805X7R105K16 NPIS73T100MTRF SMD 10k@25C 0805 NTC Thermistor Resistor +/- 1% Resistor +/- 1% Resistor +/- 1% Rapid 18-3505 Manufacturer DIODES / ZETEX DIODES / ZETEX DIODES / ZETEX DIODES / ZETEX Kemet Murata NIC Kemet Murata NIC NIC generic generic generic generic generic generic Keystone Quantity 1 1 1 1 2 1 1 0 0 1 1 1 1 1 ZXLD1360EV6 Connection Point Definition Description Positive supply voltage. Supply Ground (0V). To monitor the voltage across the current sense resistor R6 Can be used to supply an Enable voltage if solder link P4 is opened. External LED +ve External LED -ve The socket is designed to accept an LED Module Board. The pins are: 5 ,6, 7, 8 = LED cathode (-ve) and 1, 2, 11, 12 = LED anode (+ve). Pins 3, 4, 9, and 10 are not used. Issue 1 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 4 ZXSC310EV6 ZXLD1360EV6 Basic operation at 1.5V WARNING: Exposed battery connections exist on the front and back of the board. Do not cause the batteries to short-circuit by placing it on a conductive surface or allowing other conductive materials to come into contact with it. 1. Connect a power supply to TP3 (+ve) and TP4 (-ve) or insert an ‘AA’ size battery as depicted on the top of the board . Warning: The board does not have reverse battery/supply protection. 2. Set the PSU (if used), to 1.5V 3. Connect a suitable LED board to connector SK1, or an extyernal LED to LED+ and LED-. . (The LED must be capable of handling 600mA) 4. Turn on the PSU (if used), and the switch SW1. The LED will illuminate and the current should be approximately 600mA. Warning: Do not look at the LED directly. ZXSC310 Device Packages, Pin and Definitions ZXSC310 Vcc 1 GND 2 En 3 5 Vdrive 4 Vsense SOT23-5 package ZXLD1360 Device Pin Definition Name Pin No Description VCC 1 Input Voltage GND 2 Ground (0V). Enable 3 Tie high for normal operation, low to shutdown Vsense 4 From the sense resistor Vdrive 5 Drive current output to transistor Issue 1 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 5 ZXSC310EV6 ZXSC310 Operation The ZXSC310 is a constant off-time converter (also known as PFM). It operates as follows:On switch on, Q1 is switched on and the current through the inductor rises until the voltage across the sense resistor R6 reaches the threshold (set by the device to about 20mV). Q1 is then switched off for a constant time (determined by the internal device characteristics ) of about 1.5us. During this time the inductor partially discharges into the load. After the off-time, the cycle repeats. It is worth noting that the frequency is determined by the ratio of the input voltage to the load voltage (and the fixed off-time) and does not depend on the inductor value. Test and Diagnostics With this type of circuit the performance is best evaluated by watching the waveform on the current sensing resistor. A test pad (TP1) has been provided for this purpose. The voltage is normally 0-20mV so a sensitive oscilloscope with fairly narrow bandwidth is ideal. This waveform with a corresponding inductor current waveform is shown schematically in Fig 5 188.8320u 196.7942u I(L1-P) / mA 7.962140u 900 800 700 600 500 400 300 200 Inductor current 8.697934m Vsense U2-Vsense / mV 20 19.13537m 15 10.43743m 10 5 0 184 186 188 190 REF 192 194 196 198 200 A Time/uSecs 2uSecs/div Figure 5: Sample Waveforms Issue 1 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 6 ZXSC310EV6 Interpretation The upper curve is the inductor current and this is not easy to measure without disturbing the circuit operation. The lower curve is the voltage across the sense resistor which actually contains more information, but is less easy to interpret. This is the curve that can be seen from the test pad TP1. The first thing to notice about this waveform is that the current starts from a non-zero value at the start of the on period. This shows that the circuit is operating in continuous mode. The current rise on the lower trace looks straight which shows that the inductor resistance is not very high: if the resistances were high, the trace would sag towards the high current end and the circuit efficiency would be poor. The voltage in the off period is close to zero, which shows that the transistor Vcesat is not reducing the efficiency significantly. The ratio to on and off period is clearly defined showing that the circuit is operating cleanly. If the waveforms were not well defined there would be a fault in the operation; possibly too low an input Voltage The maximum Voltage is about 20mV showing that the peak current is at the design level. The minimum Voltage during the on period is about 10mV, so that the minimum current in this example is 500mA, and hence the average input current in this example is 750mA . Issue 1 – February 2009 www.zetex.com www.diodes.com © Diodes Incorporated 2009 7 ZXSC310EV6 Definitions Product change Diodes Incorporated reserves the right to alter, without notice, specifications, design, price or conditions of supply of any product or service. Customers are solely responsible for obtaining the latest relevant information before placing orders. Applications disclaimer The circuits in this design/application note are offered as design ideas. It is the responsibility of the user to ensure that the circuit is fit for the user’s application and meets with the user’s requirements. No representation or warranty is given and no liability whatsoever is assumed by Diodes Inc. with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Diodes Inc. does not assume any legal responsibility or will not be held legally liable (whether in contract, tort (including negligence), breach of statutory duty, restriction or otherwise) for any damages, loss of profit, business, contract, opportunity or consequential loss in the use of these circuit applications, under any circumstances. Life support Diodes Zetex products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein: A. Life support devices or systems are devices or systems which: 1. are intended to implant into the body or 2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. Reproduction The product specifications contained in this publication are 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. Terms and Conditions All products are sold subjects to Diodes Inc. terms and conditions of sale, and this disclaimer (save in the event of a conflict between the two when the terms of the contract shall prevail) according to region, supplied at the time of order acknowledgement. For the latest information on technology, delivery terms and conditions and prices, please contact your nearest Diodes sales office. 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Devices suspected of being affected should be replaced. Green compliance Diodes Zetex Semiconductors is committed to environmental excellence in all aspects of its operations which includes meeting or exceeding regulatory requirements with respect to the use of hazardous substances. Numerous successful programs have been implemented to reduce the use of hazardous substances and/or emissions. All Diodes Zetex components are compliant with the RoHS directive, and through this it is supporting its customers in their compliance with WEEE and ELV directives. Product status key: “Preview” “Active” “Last time buy (LTB)” “Not recommended for new designs” “Obsolete” Datasheet status key: “Draft version” “Provisional version” “Issue” Future device intended for production at some point. Samples may be available Product status recommended for new designs Device will be discontinued and last time buy period and delivery is in effect Device is still in production to support existing designs and production Production has been discontinued This term denotes a very early datasheet version and contains highly provisional information, which may change in any manner without notice. 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. This term denotes an issued datasheet containing finalized specifications. However, changes to specifications may occur, at any time and without notice. Sales offices The Americas Europe Taiwan Shanghai Shenzhen Korea 3050 E. 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