ZXSC440 PHOTOFLASH CHARGER DESCRIPTION The ZXSC440 is a dedicated photoflash charger, charging an 80F photoflash capacitor to 300V in 3.5 seconds from a 3V supply. 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 from the camera's microprocessor, using negligible current when flash is not being used. 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 80F photoflash capacitor to 300V in • Digital camera flash unit 3.5 seconds from 3V • Film camera flash unit • Charges various value photoflash capacitors • Over 75% flyback efficiency • Charge and Ready pins TYPICAL APPLICATION CIRCUIT • Consumes only 4.5A when not charging • Small MSOP8 low profile package PINOUT MSOP8 pin TOP VIEW ORDERING INFORMATION DEVICE ZXSC440X8TA ZXSC440X8TC DEVICE DESCRIPTION TEMPERATURE RANGE PART MARK TAPING OPTIONS Camera flash charger -40°C to +85°C ZXSC440 TA, TC • TA reels hold 1000 devices • TC reels hold 4000 devices DRAFT ISSUE F - MAY 2004 1 SEMICONDUCTORS ZXSC440 ABSOLUTE MAXIMUM RATINGS PARAMETER LIMIT V CC -0.3 to +10 UNIT V DRIVE V READY -0.3 to V CC + 0.3 -0.3 to V CC + 0.3 CHARGE -0.3 to The lower of (+5.0) or (V CC +0.3) V V FB , SENSE -0.3 to The lower of (+5.0) or (V CC +0.3) V Operating temperature -40 to +85 °C Storage temperature -55 to +150 °C Power dissipation at 25°C 450 V mW ELECTRICAL CHARACTERISTICS (Test conditions VCC= 3V, T= 25°C unless otherwise stated) SYMBOL PARAMETER V CC V CC range Iq (1) Quiescent current I STDN Shutdown current Eff (2) CONDITIONS MIN. V CC =8V Reference tolerance TCO REF Reference temp co T DRV Discharge pulse width F OSC Operating frequency MAX. V 220 A A 85 1.8V < V CC < 8V -3.0 % 3.0 0.005 1.8V < V CC < 8V UNIT 8 4.5 Efficiency Acc REF TYP. 1.8 % %/°C s 1.7 200 kHz mV INPUT PARAMETERS V SENSE Sense voltage I SENSE Sense input current V FB Feedback voltage I FB (2) Feedback input current VIH (3) Shutdown threshold VIL Shutdown threshold dV LN Line voltage regulation V FB =0V;V SENSE =0V V FB =0V;V SENSE =0V 22 28 34 -1 -7 -15 A 291 300 309 mV -1.2 -4.5 A 1.5 VCC V 0 0.55 0.5 V %/V OUTPUT PARAMETERS I DRIVE Transistor drive current V DRIVE Transistor voltage drive C DRIVE Mosfet gate drive cpbty VOH READY Ready flag output high IEOR = -300nA, T A =25°C VOL READY Ready flag output low I EOR = 1mA, T A =25°C T A =25°C T READY dI LD V DRIVE = 0.7V 2 3.4 0 5 VCC-0.4 300 Load current regulation mA V pF 2.5 VCC V 0 1 V 0.01 %/mA s 195 NOTES (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. DRAFT ISSUE F - MAY 2004 SEMICONDUCTORS 2 ZXSC440 ABSOLUTE MAXIMUM RATINGS PIN # NAME DESCRIPTION 1 DRIVE Drive output for external switching transistor. Connect to base or gate of external switching transistor 2 V FB Reference voltage. Internal threshold set to 300mV. Connect external resistor network to set output voltage 3 SENSE Inductor current sense input. Internal threshold voltage set to 28mV. Connect external sense resistor 4 N/C 5 CHARGE Initiate photoflash capacitor charging 6 READY Signal to microprocessor when photoflash capacitor charged 7 GND Ground 8 V CC Supply voltage, 1.8V to 8V BLOCK DIAGRAM DRAFT ISSUE F - MAY 2004 3 SEMICONDUCTORS ZXSC440 DEVICE DESCRIPTION READY detector The READY circuit is a re-triggerable 195s 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 195s are ignored. If the output voltage falls below the nominal value for more than 195s, 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. 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 ±2A. 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 1.7s. The inductor discharges into the reservoir capacitor. After 1.7s 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. DRAFT ISSUE F - MAY 2004 SEMICONDUCTORS 4 ZXSC440 TYPICAL OPERATING CHARACTERISTICS (For typical application circuit at VIN=3V and TA=25 °C unless otherwise stated) DRAFT ISSUE F - MAY 2004 5 SEMICONDUCTORS ZXSC440 APPLICATIONS 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. Peak current definition 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 I PK is decided the value of R SENSE can be determined by: V SENSE RSENSE = I PK 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 voltage multiplied by the step-up ratio of the transformer: VR(DIODE) = VOUT(MAX) + (VIN x TURNSRATIO) 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: Manufacturer Series R DC ( ) Range Size Tolerance URL Cyntec RL1220 0.022 - 10 0805 ±5% http://www.cyntec.com IRC LR1206 0.010 - 1.0 1206 ±5% http://www.irctt.com Using a 22m⍀ sense resistor results in a peak current of just over 1.2A. DRAFT ISSUE F - MAY 2004 SEMICONDUCTORS 6 ZXSC440 Transformer parameters Proprietary transformers are available, for example the Pulse PAO367, Primary inductance: 24uH, 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 L PRI (H) L PRI -LEAK (nH) N R PRI (m⍀) 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 9.1x9.1x5.1 24 PAO367 R SEC Manufacturer (⍀) Tokyo Coil Eng. www.tokyo-coil.co.jp Kijima Musen [email protected] Pulse www.pulseeng.com 12:1 DRAFT ISSUE F - MAY 2004 7 SEMICONDUCTORS ZXSC440 Output power calculation The output voltage is determined by the equation: VOUT = VFB (1 + RA / RB), 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. 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 1000because 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 The ZXSC440 are adjustable output converters allowing the end user the maximum flexibility. For adjustable operation a potential divider network is connected as follows: DRAFT ISSUE F - MAY 2004 SEMICONDUCTORS 8 ZXSC440 Layout issues 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. Layout is critical for the circuit to function in the most efficient manner in terms of electrical efficiency, thermal considerations and noise. 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. DRAFT ISSUE F - MAY 2004 9 SEMICONDUCTORS ZXSC440 REFERENCE DESIGNS General camera photoflash charger Specification VIN = VOUT = Circuit diagram 5V Efficiency = 275V 71% Charging time = 4 seconds Bill of materials Ref Value U1 Q1 D1 (2) 200V Package Part number Manufacturer MSOP8 ZXSC440 Zetex Notes SOT23 ZXMN6A07F Zetex 60V N-channel MOSFET SOT23 BAS21 Philips x2 200V fast rectifier diodes connected in series Pulse See note (1) Tx1 R1 22m⍀ 0805 RL1210 R2 10M⍀/400V Axial Generic Cyntec Generic R3 10k⍀ 0805 Generic Generic R4 100k⍀ 0805 Generic Generic C1 100uF/10V 0805 Generic Murata C2 10pF/500V 1206 Generic Generic C3 10nF/6V3 1206 Generic Generic C4 120uF/330V Radial FW Series Rubycon Output voltage across resistor Output voltage seen across capacitor Photoflash capacitor NOTES: (1) Transformer specification: Primary inductance: 24uH, Core: Pulse PAO367, Turns ratio: 1:12 (2) 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. DRAFT ISSUE F - MAY 2004 SEMICONDUCTORS 10 ZXSC440 High power digital camera photoflash charger Specification Circuit diagram VIN = 3V VOUT = Efficiency = 275V 69% Charging time = 5 seconds Bill of materials Ref Package Part number Manufacturer U1 Value MSOP8 ZXSC440 Zetex Notes U2 SOT23-6 ZXTD6717 Zetex NPN/PNP dual Q1 SOT23 FMMT619 Zetex 50V NPN low sat SOT23 BAS21 Philips 200V fast rectifier D1 200V D2 200V SOT23 BAS21 Philips 200V fast rectifier D3 2A SOT23-6 ZLLS2000 Zetex 2A Schottky diode PAO367 Pulse See note (1) RL1210 Cyntec Tx1 R1 22m⍀ 0805 R2 130⍀ 0805 Generic Generic R3 2k2⍀ 0805 Generic Generic R4 10M⍀/400V Axial Generic Generic R5 10k⍀ 0805 Generic Generic C1 100uF/10V 0805 Generic Murata C2 220nF 0805 GRM Series Murata C3 10pF/500V 1206 Generic Generic C4 10nF/6V3 1206 Generic Generic C5 120uF/330V Radial FW Series Rubycon Output voltage across resistor Output voltage seen across capacitor Photoflash capacitor NOTES: (1) Transformer specification: Primary inductance: 24uH, Core: Pulse PAO367, Turns ratio: 1:12 DRAFT ISSUE F - MAY 2004 11 SEMICONDUCTORS ZXSC440 Low power digital camera photoflash charger Specification VIN = 3V VOUT = Efficiency = 275V 58% Charging time = 6.8 seconds Circuit diagram Bill of materials Ref Package Part number Manufacturer U1 Value MSOP8 ZXSC440 Zetex Notes U2 SOT23-6 ZXTD6717 Zetex NPN/PNP dual Q1 SOT23 FMMT619 Zetex 50V NPN low sat 200V fast rectifier D1 200V SOT23 BAS21 Philips D2 200V SOT23 BAS21 Philips 200V fast rectifier D3 2A SOT23-6 ZLLS2000 Zetex 2A Schottky diode Sumida See note (1) Tx1 R1 33m⍀ 0805 RL1210 Cyntec R2 200⍀ 0805 Generic Generic R3 2k2⍀ 0805 Generic Generic R4 10M⍀/400V Axial Generic Generic R5 10k⍀ 0805 Generic Generic C1 100uF/10V 0805 Generic Murata C2 220nF 0805 GRM Series Murata C3 10pF/500V 1206 Generic Generic C4 10nF/6V3 1206 Generic Generic C5 80uF/330V Radial FW Series Rubycon Output voltage across resistor Output voltage seen across capacitor Photoflash capacitor NOTES: (1) Transformer specification: Primary inductance: 32uH, Core: Sumida CEEH64, Turns ratio: 1:10 DRAFT ISSUE F - MAY 2004 SEMICONDUCTORS 12 ZXSC440 PACKAGE OUTLINE e c 8 R1 L E1 E 15%%D MAX R 1 GAGE PLANE D A2 A 0.25 INDENT AREA (D/2 X E1/2) 0%%D-6%%D A1 b Controlling dimensions are in millimeters. Approximate conversions are given in inches PACKAGE DIMENSIONS Millimeters Inches DIM Millimeters Inches DIM Min Max Min Max Min A - 1.10 - 0.0433 E A1 0.05 0.15 0.002 0.006 E1 A2 0.75 0.95 0.0295 0.0374 e Max 4.90 BSC 2.90 3.10 0.65 BSC Min Max 0.025 BSC 0.114 0.122 0.193 BSC b 0.25 0.40 0.010 0.0157 L 0.40 0.70 0.0157 0.0192 c 0.13 0.23 0.005 0.009 R 0.07 - 0.0027 - © Zetex plc 2004 Europe Americas Asia Pacific Corporate Headquaters Zetex GmbH Streitfeldstraße 19 D-81673 München Germany Zetex Inc 700 Veterans Memorial Hwy Hauppauge, NY 11788 USA Zetex (Asia) Ltd 3701-04 Metroplaza Tower 1 Hing Fong Road, Kwai Fong Hong Kong Zetex plc Fields New Road, Chadderton Oldham, OL9 8NP United Kingdom Telephone: (852) 26100 611 Telephone: (1) 631 360 2222 Telefon: (49) 89 45 49 49 0 Fax: (852) 24250 494 Fax: (1) 631 360 8222 Fax: (49) 89 45 49 49 49 [email protected] [email protected] [email protected] These offices are supported by agents and distributors in major countries world-wide. Telephone (44) 161 622 4444 Fax: (44) 161 622 4446 [email protected] 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. For the latest product information, log on to www.zetex.com DRAFT ISSUE F - MAY 2004 13 SEMICONDUCTORS