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ZXSC440
PHOTOFLASH CHARGER
DESCRIPTION
The ZXSC440 is a dedicated photoflash charger, charging an 80 F 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
* Charges a 80 F photoflash capacitor to 300V in
3.5 seconds from 3V
APPLICATIONS
* Digital camera flash unit * Film camera flash unit
* Charges various value photoflash capacitors * Over 75% flyback efficiency * Charge and Ready pins * Consumes only 4.5 A when not charging * Small MSOP8 low profile package
TYPICAL APPLICATION CIRCUIT
PINOUT
MSOP8 pin TOP VIEW
ORDERING INFORMATION
DEVICE ZXSC440X8TA ZXSC440X8TC DEVICE DESCRIPTION TEMPERATURE RANGE PART MARK ZXSC440 TAPING OPTIONS TA, TC
Camera flash charger
-40C to +85C
* TA reels hold 1000 devices * TC reels hold 4000 devices
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ABSOLUTE MAXIMUM RATINGS
PARAMETER V CC DRIVE READY CHARGE V FB , SENSE Operating temperature Storage temperature Power dissipation at 25C LIMIT -0.3 to +10 -0.3 to V CC + 0.3 -0.3 to V CC + 0.3 -0.3 to The lower of (+5.0) or (V CC +0.3) -0.3 to The lower of (+5.0) or (V CC +0.3) -40 to +85 -55 to +150 450 UNIT V V V V V C C mW
ELECTRICAL CHARACTERISTICS (Test conditions VCC= 3V, T= 25C unless otherwise stated)
SYMBOL V CC Iq (1) I STDN Eff (2) Acc REF TCO REF T DRV F OSC INPUT PARAMETERS V SENSE I SENSE V FB I FB (2) VIH (3) VIL dV LN OUTPUT PARAMETERS I DRIVE V DRIVE C DRIVE VOH READY VOL READY T READY dI LD Load current regulation Transistor drive current Transistor voltage drive Mosfet gate drive cpbty Ready flag output high Ready flag output low IEOR = -300nA, T A =25C I EOR = 1mA, T A =25C T A =25C 2.5 0 195 0.01 V DRIVE = 0.7V 2 0 300 VCC 1 3.4 5 VCC-0.4 mA V pF V V s %/mA Sense voltage Sense input current Feedback voltage Feedback input current Shutdown threshold Shutdown threshold Line voltage regulation V FB =0V;V SENSE =0V V FB =0V;V SENSE =0V 22 -1 291 -1.2 1.5 0 0.5 28 -7 300 34 -15 309 -4.5 VCC 0.55 mV A mV A V V %/V PARAMETER V CC range Quiescent current Shutdown current Efficiency Reference tolerance Reference temp co Discharge pulse width Operating frequency 1.8V < V CC < 8V 1.8V < V CC < 8V -3.0 0.005 1.7 200 V CC =8V 4.5 85 3.0 CONDITIONS MIN. 1.8 TYP. MAX. 8 220 UNIT V A A % % %/C s kHz
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.
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ZXSC440
ABSOLUTE MAXIMUM RATINGS
PIN # 1 2 3 4 5 6 7 8 NAME DRIVE V FB SENSE N/C CHARGE READY GND V CC Initiate photoflash capacitor charging Signal to microprocessor when photoflash capacitor charged Ground Supply voltage, 1.8V to 8V 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
BLOCK DIAGRAM
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ZXSC440
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 2 A. 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 1.7 s. The inductor discharges into the reservoir capacitor. After 1.7 s 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 195 s 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 195 s are ignored. If the output voltage falls below the nominal value for more than 195 s, 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.
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ZXSC440
TYPICAL OPERATING CHARACTERISTICS (For typical application circuit at VIN=3V and TA=25 C unless otherwise stated)
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APPLICATIONS
Switching transistor selection 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 SuperSOTTM 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 voltage multiplied by the step-up ratio of the transformer: VR(DIODE) = VOUT(MAX) + (VIN x TURNSRATIO) 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. 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
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 Cyntec IRC
Series RL1220 LR1206
R DC ( ) Range 0.022 - 10 0.010 - 1.0
Size 0805 1206
Tolerance 5% 5%
URL http://www.cyntec.com http://www.irctt.com
Using a 22m sense resistor results in a peak current of just over 1.2A.
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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. T-15-089 T-15-083 Size (WxLxH) mm 6.4x7.7x4 8x8.9x2 L PRI ( H) 12 20 L PRI -LEAK (nH) 400 500 N 10:2 10:2 R PRI (m ) 211 675 R SEC Manufacturer () 27 35 Tokyo Coil Eng. www.tokyo-coil.co.jp
SBL-5.6-1
5.6x8.5x4
10
200
10:2
103
26
Kijima Musen Kijimahk@netvigator.com Pulse www.pulseeng.com
PAO367
9.1x9.1x5.1
24
12:1
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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 30H primary, the stored energy will be 21.6J. The frequency is set by the time it takes the primary to reach 1.2 amps plus the 1.7s time allowed to discharge the energy into the reservoir capacitor. Using 3 volts, the ramp time is 12s, 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 80F 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 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.
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ZXSC440
Layout issues 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. 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.
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REFERENCE DESIGNS
General camera photoflash charger Specification VIN = VOUT = Efficiency = Charging time = 5V 275V 71% 4 seconds Circuit diagram
Bill of materials
Ref U1 Q1 D1 (2) Tx1 R1 R2 R3 R4 C1 C2 C3 C4 22m 10M /400V 10k 100k 100uF/10V 10pF/500V 10nF/6V3 120uF/330V 0805 Axial 0805 0805 0805 1206 1206 Radial RL1210 Generic Generic Generic Generic Generic Generic FW Series 200V Value Package MSOP8 SOT23 SOT23 Part number ZXSC440 ZXMN6A07F BAS21 Manufacturer Zetex Zetex Philips Pulse Cyntec Generic Generic Generic Murata Generic Generic Rubycon Photoflash capacitor Output voltage seen across capacitor Output voltage across resistor 60V N-channel MOSFET x2 200V fast rectifier diodes connected in series See note (1) Notes
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.
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ZXSC440
High power digital camera photoflash charger Specification VIN = VOUT = Efficiency = Charging time = 3V 275V 69% 5 seconds Circuit diagram
Bill of materials
Ref U1 U2 Q1 D1 D2 D3 Tx1 R1 R2 R3 R4 R5 C1 C2 C3 C4 C5 22m 130 2k2 10M /400V 10k 100uF/10V 220nF 10pF/500V 10nF/6V3 120uF/330V 0805 0805 0805 Axial 0805 0805 0805 1206 1206 Radial 200V 200V 2A Value Package MSOP8 SOT23-6 SOT23 SOT23 SOT23 SOT23-6 Part number ZXSC440 ZXTD6717 FMMT619 BAS21 BAS21 ZLLS2000 PAO367 RL1210 Generic Generic Generic Generic Generic GRM Series Generic Generic FW Series Manufacturer Zetex Zetex Zetex Philips Philips Zetex Pulse Cyntec Generic Generic Generic Generic Murata Murata Generic Generic Rubycon Photoflash capacitor Output voltage seen across capacitor Output voltage across resistor NPN/PNP dual 50V NPN low sat 200V fast rectifier 200V fast rectifier 2A Schottky diode See note (1) Notes
NOTES: (1) Transformer specification: Primary inductance: 24uH, Core: Pulse PAO367, Turns ratio: 1:12
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Low power digital camera photoflash charger Specification VIN = VOUT = Efficiency = Charging time = Circuit diagram 3V 275V 58% 6.8 seconds
Bill of materials
Ref U1 U2 Q1 D1 D2 D3 Tx1 R1 R2 R3 R4 R5 C1 C2 C3 C4 C5 33m 200 2k2 10M /400V 10k 100uF/10V 220nF 10pF/500V 10nF/6V3 80uF/330V 0805 0805 0805 Axial 0805 0805 0805 1206 1206 Radial RL1210 Generic Generic Generic Generic Generic GRM Series Generic Generic FW Series 200V 200V 2A Value Package MSOP8 SOT23-6 SOT23 SOT23 SOT23 SOT23-6 Part number ZXSC440 ZXTD6717 FMMT619 BAS21 BAS21 ZLLS2000 Manufacturer Zetex Zetex Zetex Philips Philips Zetex Sumida Cyntec Generic Generic Generic Generic Murata Murata Generic Generic Rubycon Photoflash capacitor Output voltage seen across capacitor Output voltage across resistor NPN/PNP dual 50V NPN low sat 200V fast rectifier 200V fast rectifier 2A Schottky diode See note (1) Notes
NOTES: (1) Transformer specification: Primary inductance: 32uH, Core: Sumida CEEH64, Turns ratio: 1:10
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ZXSC440
PACKAGE OUTLINE
e
c
8
15%%D MAX
E1
E
R1
R 1 GAGE PLANE 0.25
D
A2
INDENT AREA (D/2 X E1/2) A1 b
A
0%%D-6%%D
Controlling dimensions are in millimeters. Approximate conversions are given in inches
PACKAGE DIMENSIONS
Millimeters DIM Min A A1 A2 b c 0.05 0.75 0.25 0.13 Max 1.10 0.15 0.95 0.40 0.23 Min 0.002 0.0295 0.010 0.005 Max 0.0433 0.006 0.0374 0.0157 0.009 E E1 e L R Inches DIM Min Max Min Max 4.90 BSC 2.90 3.10 0.025 BSC 0.114 0.122 Millimeters Inches
0.65 BSC 0.40 0.07 0.70 -
0.193 BSC 0.0157 0.0027 0.0192 -
(c) Zetex plc 2004
Europe Zetex GmbH Streitfeldstrae 19 D-81673 Munchen Germany Americas Zetex Inc 700 Veterans Memorial Hwy Hauppauge, NY 11788 USA Asia Pacific Zetex (Asia) Ltd 3701-04 Metroplaza Tower 1 Hing Fong Road, Kwai Fong Hong Kong Corporate Headquaters Zetex plc Fields New Road, Chadderton Oldham, OL9 8NP United Kingdom Telephone (44) 161 622 4444 Fax: (44) 161 622 4446 hq@zetex.com
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 asia.sales@zetex.com usa.sales@zetex.com europe.sales@zetex.com These offices are supported by agents and distributors in major countries world-wide.
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
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