ZXSC440

ZXSC440

Document overview

• Manufacturer or author: Diodes Incorporated
• PDF pages: 11

Technical content

Features

• Charges a 80µF photoflash capacitor to 300V in 3.5 seconds from 3V
• Charges various value photoflash capacitors
• Over 75% flyback efficiency
• Charge and Ready pins
• Consumes only 4.5µA when not charging
• Small MSOP-8 low profile package Pin Assignments

Applications

• Digital camera flash unit
• Film camera flash unit Typical Application Circuit (Top View) MSOP-8 VCC GND READY CHARGE VFB DRIVE SENSE N/C

Document number: DS33619 Rev. 3 - 2 2 of 11 www.diodes.com June 2012 © Diodes Incorporated ADVANCE INFORMATION Pin Descriptions Pin Name Pin # Description Drive 1 Drive output for external switching transistor. Connect to base or gate of external switching transistor VFB 2 Reference voltage. Internal threshold set to 300mV. Connect external resistor network to set output voltage Sense 3 Inductor current sense input. Internal threshold voltage set to 28mV. Connect external sense resistor N/C 4 Charge 5 Initiate photoflash capacitor charging Ready 6 Signal to microprocessor when photoflash capacitor charged GND 7 Ground VCC 8 Supply voltage, 1.8V to 8V Functional Block Diagram

Document number: DS33619 Rev. 3 - 2 3 of 11 www.diodes.com June 2012 © Diodes Incorporated ADVANCE INFORMATION Absolute Maximum Ratings (TA = 25°C) Parameter Rating Unit VCC -0.3 to +10 V Drive -0.3 to VCC +0.3 V Ready -0.3 to VCC +0.3 V Charge -0.3 to The lower of (+5.0) or (VCC +0.3) V VFB, Sense -0.3 to The lower of (+5.0) or (VCC +0.3) V Operating Temperature -40 to +85 °C Storage Temperature -55 to +150 °C Power Dissipation @ 25°C 450 mW Electrical Characteristics (TA = 25°C, Vdd = 3V; unless otherwise specified) Symbol Parameter Conditions Min. Typ. Max. Unit VCC V CC range 1.8 8 V IQ (Note 1) Quiescent current VCC = 8V 220 µA ISTDN Shutdown current 4.5 µA EFF (Note 2) Efficiency 85 % ACCREF Reference tolerance 1.8V < VCC < 8V -3.0 3.0 % TCOREF Reference temp co. 0.005 %/°C TDRV Discharge pulse width 1.8V < VCC < 8V 1.7 µs FOSC Operating frequency 200 kHz INPUT PARAMETERS VSENSE Sense voltage 22 28 34 mV ISENSE Sense input current VFB = 0V; VSENSE = 0V -1 -7 -15 µA VFB Feedback volatage 291 300 309 mV IFB (Note 2) Feedback input current VFB = 0V; VSENSE = 0V -1.2 -4.5 µA VIH (Note 3) Shutdown threshold 1.5 VCC V VIL Shutdown threshold 0 0.55 V dVLN Line voltage regulation 0.5 %/V OUTPUT PARAMETERS IDRIVE Transistor drive current VDRIVE = 0.7V 2 3.4 5 mA VDRIVE Transistor voltage drive 0 VCC-0.4 V CDRIVE MOSFET gate drive cpbty 300 pF VOHREADY Ready flag output high IEOR = -300nA, TA = 25°C 2.5 VCC V VOLREADY Ready flag output low IEOR = 1mA, TA = 25°C 0 1 V TREADY TA = 25°C 195 µs dILD Load current regulation 0.01 %/mA Notes: 1. Excluding gate/base drive current. 2. I FB is typically half of these at 3V. 3. Shutdown pin voltage must not exceed (V CC+0.3V) or 5V, whichever is lower.

Document number: DS33619 Rev. 3 - 2 4 of 11 www.diodes.com June 2012 © Diodes Incorporated ADVANCE INFORMATION Device Description Bandgap Reference All threshold voltages and internal currents are derived from a temperature compensated bandgap reference circuit with a reference voltage of 1.22V nominal. If the REF terminal is used as a reference for external devices, the maximum load should not exceed ±2µA. Dynamic Drive Output Depending on the input signal, the output is either "LOW" or "HIGH". In the high state a 3.4mA current source (max drive voltage = V CC-0.4V) drives the base or gate of the external transistor. In order to operate the external switching transistor at opt imum efficiency, both output states are initiated with a short transient current in order to quickly discharge the base or the gate of the switching transistor. Switching Circuit The switching circuit consists of two comparators, Comp1 and Comp2, a gate U1, a monostable and the drive output. Normally the DRIVE output is "HIGH"; the external switching transistor is turned on. Current ramps up in the inductor, the switching tran sistor and external current sensing resistor. This voltage is sensed by comparator, Comp2, at input SENSE. Once the current sense voltage across the sensing resistor exceeds 28mV, comparator, Comp2, through gate U1, triggers a re-triggerable monostable and turns off the output drive stage for 1.7µs. The inductor discharges into the reservoir capacitor. After 1.7µs a new charge cycle begi ns, thus ramping the output voltage. When the output vo ltage reaches the nominal value and VFB gets an input voltage of more than 300mV, the monostable is forced "on" from Comp1 through gate U1, until the feedback volta ge falls below 300mV. The above action continues to maintain regulation, with slight hysteresis on the feedback threshold. READY Detector The READY circuit is a re-triggerable 195µs monostable, which is re-triggered by every down regulating action of comparator Comp1. As long as regulation takes place, output READY is "HIGH" (high impedance, 100K to V CC). Short dips of the output vo ltage of less than 195µs are ignored. If the output voltage falls below the nominal value for more than 195µs, output READY goes "LOW". This can be used to signal to the camera controller that the flash unit has charged fully and is ready to use. Typical Operating Characteristics (For typical application circuit at VIN=3V and TA=25°C unless otherwise stated)

Document number: DS33619 Rev. 3 - 2 5 of 11 www.diodes.com June 2012 © Diodes Incorporated ADVANCE INFORMATION

Application Information

Switching Transistor Selection The choice of switching transistor has a major impact on the converter efficiency. Fo r optimum performance, a bipolar transistor with low V CE(SAT) and high gain is required. The V CEO of the switching transistor is also an important parameter as this s ees typically three times the input voltage when the transistor is switched off. Zetex SuperSOT™ transistors are an ideal choice for this application. At input voltages above 4V, suitable Zetex MOSFET transistors will give almost the same performance with a simpler drive circuit, omitting the ZXTD6717 pre-drive stage. Using a MOSFET, the Schottky diode may be omitted, as the body diode of the MOSFET will perform the same function, with just a small loss of efficiency. Output Rectifier Diode Selection The diode should have a fast recovery, as any time spent in reverse conduction removes energy from the reservoir capacitor and dumps it, via the transformer, into the protection diode across the output transistor. This seriously reduces efficiency. Two BAS21 diodes in series have been used, bearing in mind that the reverse voltage across the diode is the sum of the output voltage together with the input volta ge multiplied by the step-up ratio of the transformer: VR(DIODE) = VOUT(MAX) + (VIN x TURNS RATIO) Therefore, with a 300V outpu t, a supply of 8 volts and a 1:12 step-up transformer, there will be a 396V across the diode. This occurs during the current ramp-up in the primary, as it transforms the input voltage up by the turns ratio and the polarity at the secondary is such as to add to the output voltage already being held off by the diode. Peak Current Definition In general, the I PK value must be chosen to ensure that the switching transistor, Q1, is in full saturation with maximum output power condit ions, assuming worse-case input voltage and transistor gain under all operating temperature extremes. Once I PK is decided the value of RSENSE can be determined by: I VR PK SENSE SENSE = Sense Resistor A low value sense resistor is required to set the peak current. Power in this resistor is negligible due to the low sense voltage threshold, V SENSE. Below is a table of recommended sense resistors: Manufacturer Series RDC(Ω) Range Size Tolerance Cyntec RL1220 0.022 - 10 0805 ±5% IRC LR1206 0.010 – 1.0 1206 ±5% Using a 22mΩ sense resistor results in a peak current of just over 1.2A. Transformer Parameters Proprietary transformers are available, for example the Pulse PAO367, Primary inductance: 24µH, Core: Pulse PAO367, Turns ratio: 1:12, see Bill of Materials below. If designing a transformer, bear in mind that the primary current may be over an amp and, if this flows through 10 turns, the primary flux will be 10 Amp. Turns and small cores will need an air gap to cope with this value without saturation. Secondary winding capacitance should not be too high as this is working at 300V and could soon cause excessive losses. ZXSC440 Transformer Specifications Part No. Size (WxLxH) mm LPRI (µH) LPRI-LEAK (nH) N RPRI (mΩ) RSEC (Ω) T-15-089 6.4x7.7x4 12 400 10:2 211 27 T-15-083 8x8.9x2 20 500 10:2 675 35 SBL-5.6-1 5.6x8.5x4 10 200 10:2 103 26 PAO367 9.1x9.1x5.1 24 12:1

Document number: DS33619 Rev. 3 - 2 6 of 11 www.diodes.com June 2012 © Diodes Incorporated ADVANCE INFORMATION Application Information (cont.) Output Power Calculation This is approximately the power stored in the coil times the frequency of operation times the efficiency. Assuming a current of 1.2 amps in a 30 μH primary, the stored energy will be 21.6μJ. The frequency is set by the time it takes the primary to reach 1.2 amps plus the 1.7μs time allowed to discharge the energy into the reservoir capacitor. Using 3 volts, the ramp time is 12 μs, so the frequency will be 73kHz, giving an input power of about 1.6 watts. With an efficiency of 75% the output power will be 1.2 watts. An 80μF capacitor charged to 300 volts stores 3.6J, so 1.2 watts will take 3 seconds to charge it. Higher input voltages reduce the ramp time, the frequency therefore goes up and the output power is increased, resulting in shorter charging times. Output Voltage Adjustment The ZXSC440 are adjustable output converters allowing the end user the maximum flexibility. For adjustable operation a potential divider network is connected as follows: The output voltage is determined by the equation: VOUT = VFB (1 + RA / RB), where VFB=300mV In a circuit giving 300 volts, the "1" in the above equation becomes negligible compared to the ratio which is around 1000. It will not be exactly 1000 because of the negative input current in the feedback pin. The resistor values, RA and RB, should be maximized to improve efficiency and decrease battery drain. Optimization can be achieved by providing a minimum current of I FB(MAX)=200nA to the VFB pin. Output is adjustable from V FB to the (BR)V CEO of the switching transistor, Q1. In practice, there will be some stray capacitance across RA and this will cause a lead in the feedback which can affect hysteresis (it makes the device shut down too early) and it is best to swamp this with a capacitor CA and then use a capacitor CB across RB where CB/CA = RA/RB. This is similar to the method used for compensating oscilloscope probes. Layout Issues Layout is critical for the ci rcuit to function in the most efficient manner in terms of electrical efficiency, thermal considerations and noise. For 'step-up converters' there ar e four main current loops, the input loop, power-switch loop, rectifier loop and output loop. The supply charging the input capacitor forms the input loop. The power-switch loop is defined when Q1 is 'on', current flows from the input through the transformer primary, Q1, R SENSE and to ground. When Q1 is 'off', the energy stored in the transformer is transferred from the secondary to the output capacitor and load via D1, forming the rectifier loop. The output loop is formed by the output capacitor supplying the load when Q1 is switched back off. To optimize for best performance each of these loops kept separate from each other and interconnected with short, thick traces thus minimizing parasitic inductance, capacitance and resistance. Also the R SENSE resistor should be connected, with minimum trace length, between emitter lead of Q1 and ground, again minimizing stray parasitics.

Document number: DS33619 Rev. 3 - 2 7 of 11 www.diodes.com June 2012 © Diodes Incorporated ADVANCE INFORMATION APPLICATION CIRCUITS General Camera Photoflash Charger Specification VIN = 5V VOUT = 275V Efficiency = 71% Charging time = 4 seconds Bill of Materials Ref Value Package Part Number Manufacturer Notes U1 MSOP-8 ZXSC440 Diodes Q1 SOT23 ZXMN6A07F Diodes 60V N-Channel D1 (Note 5) 200V SOT23 BAS21 Diodes X2 200V fast rectifier diodes connected in series Tx1 Pulse (See Note 4) R1 22m Ω 0805 RL1210 Cyntec R2 10M Ω/400V Axial Generic Generic Ou tput voltage across resistor R3 10k Ω 0805 Generic Generic R4 100k Ω 0805 Generic Generic C1 100µF/10V 0805 Generic Murata C2 10pF/500V 1206 Generic Generic Ou tput voltage seen across capacitor C3 10nF/6V3 1206 Generic Generic C4 120µF/300V Radial FW Series Rubycon Photoflash Notes: 4. Transformer specification: Primary inducta nce: 24µH, Core: Pulse PAO367, Turns ratio: 1:12 5. Two BAS21 200V rectifier diodes are connected in series and us ed in place of a 400V rectifier diode to provide faster switching speeds and higher efficiency.

Document number: DS33619 Rev. 3 - 2 8 of 11 www.diodes.com June 2012 © Diodes Incorporated ADVANCE INFORMATION APPLICATION CIRCUITS (cont.) High Power Digital Camera Photoflash Charger Specification VIN = 3V VOUT = 275V Efficiency = 69% Charging time = 5 seconds Bill of Materials Ref Value Package Part Number Manufacturer Notes U1 MSOP-8 ZXSC440 Diodes U2 SOT26 ZXTD6717 Diodes NPN/PNP dual Q1 SOT23 FMMT619 Diodes 50V NPN low sat D1 200V SOT23 BAS21 Diodes 200V fast rectifier D2 200V SOT23 BAS21 Diodes 200V fast rectifier D3 2A SOT26 ZLLS2000 Diodes 2A Schottky diode Tx1 PAO367 Pulse (See note 4) R1 22m Ω 0805 RL1210 Cyntec R2 130Ω 0805 Generic Generic R3 2k2Ω 0805 Generic Generic R4 100M Ω/400V Axial Generic Generic Ou tput voltage across resistor R5 10k Ω 0805 Generic Generic C1 100µF/10V 0805 Generic Murata C2 220nF 0805 GRM Series Murata C3 10pF/500V 1206 Generic Generic Ou tput voltage seen across capacitor C4 10nF/6V3 1206 Generic Generic C5 120µF/330V Radial FW Series Rubycon Photoflash capacitor Notes: 4. Transformer specification: Primary inducta nce: 24µH, Core: Pulse PAO367, Turns ratio: 1:12

Document number: DS33619 Rev. 3 - 2 9 of 11 www.diodes.com June 2012 © Diodes Incorporated ADVANCE INFORMATION APPLICATION CIRCUITS (cont.) Low Power Digital Camera Photoflash Charger Specification VIN = 3V VOUT = 275V Efficiency = 58% Charging time = 6.8 seconds Bill of Materials Ref Value Package Part Number Manufacturer Notes U1 MSOP-8 ZXSC440 Diodes U2 SOT26 ZXTD6717 Diodes NPN/PNP dual Q1 SOT23 FMMT619 Diodes 50V NPN low sat D1 200V SOT23 BAS21 Diodes 200V fast rectifier D2 200V SOT23 BAS21 Philips 200V fast rectifier D3 2A SOT26 ZLLS2000 Diodes 2A Schottky diode Tx1 PAO367 Pulse (See note 4) R1 22m Ω 0805 RL1210 Cyntec R2 130Ω 0805 Generic Generic R3 2k2Ω 0805 Generic Generic R4 100M Ω/400V Axial Generic Generic Ou tput voltage across resistor R5 10k Ω 0805 Generic Generic C1 100µF/10V 0805 Generic Murata C2 220nF 0805 GRM Series Murata C3 10pF/500V 1206 Generic Generic Ou tput voltage seen across capacitor C4 10nF/6V3 1206 Generic Generic C5 120µF/330V Radial FW Series Rubycon Photoflash capacitor Notes: 4. Transformer specification: Primary inducta nce: 24µH, Core: Pulse PAO367, Turns ratio: 1:12

Document number: DS33619 Rev. 3 - 2 10 of 11 www.diodes.com June 2012 © Diodes Incorporated ADVANCE INFORMATION

Ordering Information

Device Package Code Packaging 7” Tape & Reel Quantity Part Number Suffix ZXSC440X8TA X8 MSOP-8 1000/Tape & Reel TA Package Outline Dimensions (All Dimensions in mm) Suggested Pad Layout MSOP-8 Dim Min Max T yp A - 1.10 - A1 0.05 0.15 0.10 A2 0.75 0.95 0.86 A3 0.29 0.49 0.39 b 0.22 0.38 0.30 c 0.08 0.23 0.15 D 2.90 3.10 3.00 E 4.70 5.10 4.90 E1 2.90 3.10 3.00 E3 2.85 3.05 2.95 e - - 0.65 L 0.40 0.80 0.60 a 0° 8° 4° x - - 0.750 y - - 0.750 All Dimensions in mm Dimensions Value (in mm) C 0.650 X 0.450 Y 1.350 Y1 5.300 A e Seati ng Pl ane Gauge Pl ane 0.25 L 4X10° 4X10° See Det ail C Det ail C c a E y x D b X C Y

Document number: DS33619 Rev. 3 - 2 11 of 11 www.diodes.com June 2012 © Diodes Incorporated ADVANCE INFORMATION 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 rese rve the right to make modifications, enhanc ements, improvements, corrections or ot her changes without further notice to this document and any product described herein. Diodes Incorporated does not assume any liabi lity arising out of the application or use of this document or an y product described herein; neither does Diodes Incorporated convey any license under its patent or trademark rights, nor the rights of othe rs. Any Customer or user of this document or products desc ribed herein in such applications shall assume all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated website, harmless against all damages. Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any pr oducts purchased through unauthoriz ed sales channel. Should Customers purchase or use Diodes In corporated products for any unintended or unauthorized application, Customers shall indemnify and hold Diodes Incorporated and its representatives harmless against all claims, dama ges, expenses, and attorney fee s arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized a pplication. Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and markings noted herein may also be covered by one or more United States, international or foreign trademarks. LIFE SUPPORT Diodes Incorporated products are specifica lly not authorized for use as critical co mponents 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. Customers represent that they have all necessary expertise in t he safety and regulatory ramifications of their life support dev ices or systems, and acknowledge and agree that they are solely responsi ble for all legal, regulatory and safety-related requirements concerning their products and any use of Diod es Incorporated products in such safety-c ritical, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its repr esentatives against any damages ar ising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems. Copyright © 2012, Diodes Incorporated www.diodes.com