ZXSC440 PHOTOFLASH CHARGER Description Pin Assignments The ZXSC440 is a dedicated photoflash charger,charging an 80µF photoflash capacitor to 300V in 3.5 seconds from a 3V supply. (Top View) ADVANCE INFORMATION VCC GND READY CHARGE DRIVE VFB SENSE N/C The flyback conversion efficiency is typically 75%,much higher than the commonly used discrete charging circuits. The Charge pin enables the circuit to be initiated fromthe camera's microprocessor, using negligible current when flash is not being used. MSOP-8 The Ready pin signals the microprocessor when the flash is charged and ready to be fired. A small amount of hysteresis on the voltage feedback shuts down the device as long as the capacitor remains fully charged, again using negligible current. Features Applications • • • • • • • 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 • Digital camera flash unit Film camera flash unit Typical Application Circuit ZXSC440 Document number: DS33619 Rev. 3 - 2 1 of 11 www.diodes.com June 2012 © Diodes Incorporated ZXSC440 PHOTOFLASH CHARGER ADVANCE INFORMATION Pin Descriptions Pin Name Pin # Drive 1 VFB 2 Sense 3 N/C Charge Ready GND 4 5 6 7 VCC 8 Description Drive output for external switching transistor. Connect to base or gate of external switching transistor Reference voltage. Internal threshold set to 300mV. Connect external resistor network to set output voltage Inductor current sense input. Internal threshold voltage set to 28mV. Connect external sense resistor Initiate photoflash capacitor charging Signal to microprocessor when photoflash capacitor charged Ground Supply voltage, 1.8V to 8V Functional Block Diagram ZXSC440 Document number: DS33619 Rev. 3 - 2 2 of 11 www.diodes.com June 2012 © Diodes Incorporated ZXSC440 PHOTOFLASH CHARGER Absolute Maximum Ratings (TA = 25°C) ADVANCE INFORMATION 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) Operating Temperature Storage Temperature Power Dissipation @ 25°C -40 to +85 -55 to +150 450 V °C °C mW Electrical Characteristics (TA = 25°C, Vdd = 3V; unless otherwise specified) Symbol Parameter VCC VCC range IQ (Note 1) Quiescent current ISTDN Shutdown current EFF (Note 2) Efficiency ACCREF Reference tolerance TCOREF Reference temp co. TDRV Discharge pulse width FOSC Operating frequency Conditions Min. Typ. 1.8 VCC = 8V Max. Unit 8 V 220 µA 4.5 µA 85 1.8V < VCC < 8V -3.0 % 3.0 % 0.005 1.8V < VCC < 8V %/°C 1.7 µs 200 kHz 34 mV INPUT PARAMETERS VSENSE Sense voltage ISENSE Sense input current VFB Feedback volatage IFB (Note 2) Feedback input current VIH (Note 3) Shutdown threshold VIL Shutdown threshold Line voltage regulation dVLN 22 VFB = 0V; VSENSE = 0V VFB = 0V; VSENSE = 0V 28 -1 -7 -15 µA 291 300 309 mV -1.2 -4.5 µA 1.5 VCC V 0 0.55 V 0.5 %/V OUTPUT PARAMETERS IDRIVE Transistor drive current VDRIVE Transistor voltage drive CDRIVE MOSFET gate drive cpbty VOHREADY Ready flag output high IEOR = -300nA, TA = 25°C VOLREADY Ready flag output low IEOR = 1mA, TA = 25°C TREADY 2 3.4 5 300 TA = 25°C mA VCC-0.4 0 Load current regulation dILD Notes: VDRIVE = 0.7V V pF 2.5 VCC V 0 1 V 0.01 %/mA 195 µs 1. Excluding gate/base drive current. 2. IFB is typically half of these at 3V. 3. Shutdown pin voltage must not exceed (VCC+0.3V) or 5V, whichever is lower. ZXSC440 Document number: DS33619 Rev. 3 - 2 3 of 11 www.diodes.com June 2012 © Diodes Incorporated ZXSC440 PHOTOFLASH CHARGER Device Description Bandgap Reference ADVANCE INFORMATION 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 = VCC-0.4V) drives the base or gate of the external transistor. In order to operate the external switching transistor at optimum 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 transistor 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 begins, thus ramping the output voltage. When the output voltage 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 voltage 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 VCC). Short dips of the output voltage 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) ZXSC440 Document number: DS33619 Rev. 3 - 2 4 of 11 www.diodes.com June 2012 © Diodes Incorporated ZXSC440 PHOTOFLASH CHARGER Application Information ADVANCE INFORMATION Switching Transistor Selection Therefore, with a 300V output, 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. The choice of switching transistor has a major impact on the converter efficiency. For optimum performance, a bipolar transistor with low VCE(SAT) and high gain is required. The VCEO of the switching transistor is also an important parameter as this sees 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. 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. Once IPK is decided the value of RSENSE can be determined by: Output Rectifier Diode Selection RSENSE = Peak Current Definition 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 voltage multiplied by the step-up ratio of the transformer: VSENSE IPK 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, VSENSE. Below is a table of recommended sense resistors: VR(DIODE) = VOUT(MAX) + (VIN x TURNS RATIO) Manufacturer Series RDC(Ω) Range Size Tolerance Cyntec IRC RL1220 LR1206 0.022 - 10 0.010 – 1.0 0805 1206 ±5% ±5% Using a 22mΩ sense resistor results in a peak current of just over 1.2A. Transformer Parameters 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. 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 ZXSC440 Transformer Specifications Part No. Size (WxLxH) mm LPRI (µH) LPRI-LEAK (nH) T-15-089 T-15-083 SBL-5.6-1 PAO367 6.4x7.7x4 8x8.9x2 5.6x8.5x4 9.1x9.1x5.1 12 20 10 24 400 500 200 ZXSC440 Document number: DS33619 Rev. 3 - 2 5 of 11 www.diodes.com N 10:2 10:2 10:2 12:1 RPRI (mΩ) RSEC (Ω) 211 675 103 27 35 26 June 2012 © Diodes Incorporated ZXSC440 PHOTOFLASH CHARGER Application Information (cont.) ADVANCE INFORMATION 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 30μH 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 12μs, 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. 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 IFB(MAX)=200nA to the VFB pin. Output is adjustable from VFB to the (BR)VCEO 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. Output Voltage Adjustment Layout Issues The ZXSC440 are adjustable output converters allowing the end user the maximum flexibility. For adjustable operation a potential divider network is connected as follows: Layout is critical for the circuit to function in the most efficient manner in terms of electrical efficiency, thermal considerations and noise. 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 ZXSC440 Document number: DS33619 Rev. 3 - 2 For 'step-up converters' there are 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, RSENSE 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 RSENSE resistor should be connected, with minimum trace length, between emitter lead of Q1 and ground, again minimizing stray parasitics. 6 of 11 www.diodes.com June 2012 © Diodes Incorporated ZXSC440 PHOTOFLASH CHARGER APPLICATION CIRCUITS General Camera Photoflash Charger ADVANCE INFORMATION Specification VIN = 5V VOUT = 275V Efficiency = 71% Charging time = 4 seconds Bill of Materials Ref Value U1 Q1 Package Part Number Manufacturer MSOP-8 SOT23 ZXSC440 ZXMN6A07F Diodes Diodes Diodes D1 (Note 5) 200V SOT23 BAS21 Tx1 R1 R2 R3 R4 C1 C2 C3 C4 22mΩ 10MΩ/400V 10kΩ 100kΩ 100µF/10V 10pF/500V 10nF/6V3 120µF/300V 0805 Axial 0805 0805 0805 1206 1206 Radial RL1210 Generic Generic Generic Generic Generic Generic FW Series Notes: Pulse Cyntec Generic Generic Generic Murata Generic Generic Rubycon Notes 60V N-Channel X2 200V fast rectifier diodes connected in series (See Note 4) Output voltage across resistor Output voltage seen across capacitor Photoflash 4. Transformer specification: Primary inductance: 24µH, Core: Pulse PAO367, Turns ratio: 1:12 5. Two BAS21 200V rectifier diodes are connected in series and used in place of a 400V rectifier diode to provide faster switching speeds and higher efficiency. ZXSC440 Document number: DS33619 Rev. 3 - 2 7 of 11 www.diodes.com June 2012 © Diodes Incorporated ZXSC440 PHOTOFLASH CHARGER APPLICATION CIRCUITS (cont.) High Power Digital Camera Photoflash Charger ADVANCE INFORMATION Specification VIN = 3V VOUT = 275V Efficiency = 69% Charging time = 5 seconds Bill of Materials Ref Notes: Value Package Part Number Manufacturer Diodes Diodes Diodes Diodes Diodes Diodes Pulse Cyntec Generic Generic Generic Generic Murata Murata Generic Generic Rubycon U1 U2 Q1 D1 D2 D3 Tx1 R1 R2 R3 R4 200V 200V 2A MSOP-8 SOT26 SOT23 SOT23 SOT23 SOT26 22mΩ 130Ω 2k2Ω 100MΩ/400V 0805 0805 0805 Axial ZXSC440 ZXTD6717 FMMT619 BAS21 BAS21 ZLLS2000 PAO367 RL1210 Generic Generic Generic R5 C1 C2 C3 C4 C5 10kΩ 100µF/10V 220nF 10pF/500V 10nF/6V3 120µF/330V 0805 0805 0805 1206 1206 Radial Generic Generic GRM Series Generic Generic FW Series Notes NPN/PNP dual 50V NPN low sat 200V fast rectifier 200V fast rectifier 2A Schottky diode (See note 4) Output voltage across resistor Output voltage seen across capacitor Photoflash capacitor 4. Transformer specification: Primary inductance: 24µH, Core: Pulse PAO367, Turns ratio: 1:12 ZXSC440 Document number: DS33619 Rev. 3 - 2 8 of 11 www.diodes.com June 2012 © Diodes Incorporated ZXSC440 PHOTOFLASH CHARGER APPLICATION CIRCUITS (cont.) Low Power Digital Camera Photoflash Charger ADVANCE INFORMATION Specification VIN = 3V VOUT = 275V Efficiency = 58% Charging time = 6.8 seconds Bill of Materials Ref U1 U2 Q1 D1 D2 D3 Tx1 R1 R2 R3 R4 R5 C1 C2 C3 C4 C5 Notes: Value Package Part Number Manufacturer 200V 200V 2A MSOP-8 SOT26 SOT23 SOT23 SOT23 SOT26 22mΩ 130Ω 2k2Ω 100MΩ/400V 10kΩ 100µF/10V 220nF 10pF/500V 10nF/6V3 120µF/330V 0805 0805 0805 Axial 0805 0805 0805 1206 1206 Radial ZXSC440 ZXTD6717 FMMT619 BAS21 BAS21 ZLLS2000 PAO367 RL1210 Generic Generic Generic Generic Generic GRM Series Generic Generic FW Series Diodes Diodes Diodes Diodes Philips Diodes Pulse Cyntec Generic Generic Generic Generic Murata Murata Generic Generic Rubycon Notes NPN/PNP dual 50V NPN low sat 200V fast rectifier 200V fast rectifier 2A Schottky diode (See note 4) Output voltage across resistor Output voltage seen across capacitor Photoflash capacitor 4. Transformer specification: Primary inductance: 24µH, Core: Pulse PAO367, Turns ratio: 1:12 ZXSC440 Document number: DS33619 Rev. 3 - 2 9 of 11 www.diodes.com June 2012 © Diodes Incorporated ZXSC440 PHOTOFLASH CHARGER Device Package Code Packaging ZXSC440X8TA X8 MSOP-8 Quantity 7” Tape & Reel Part Number Suffix 1000/Tape & Reel TA Package Outline Dimensions (All Dimensions in mm) D 4X 1 5 2 . 0 0° e n a l P e g u a G x E Dim A A1 A2 L a C l i a t e D 4X10° MSOP-8 Min Max 1.10 0.05 0.15 0.75 0.95 Typ 0.10 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 e n a l P g n i t a e S y 3 E b 1 3 A ADVANCE INFORMATION Ordering Information A 2 A C l c i a t e D e e S 1 E e 1 A Suggested Pad Layout C X Y 1 Y ZXSC440 Document number: DS33619 Rev. 3 - 2 10 of 11 www.diodes.com Dimensions Value (in mm) C 0.650 X 0.450 Y 1.350 Y1 5.300 June 2012 © Diodes Incorporated ZXSC440 PHOTOFLASH CHARGER IMPORTANT NOTICE ADVANCE INFORMATION 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). 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