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 Chargepin enables the circuit to be initiated from
the camera's microprocessor, using negligible current
when flash is not being used.
ZXSC440
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
shutsdownthedeviceaslongasthecapacitorremains
fully charged, again using negligible current.
FEATURES
Charges a 80F 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 4.5A when not charging
•
Small MSOP8 low profile package
APPLICATIONS
Digital camera flash unit
•
Film camera flash unit
•
TYPICAL APPLICATION CIRCUIT
PINOUT
MSOP8 pin TOP VIEW
ORDERING INFORMATION
DEVICE DEVICE DESCRIPTION TEMPERATURE RANGE PART
ZXSC440X8TA
ZXSC440X8TC
Camera flash charger -40°C to +85°C ZXSC440 TA, TC
MARK
TAPING
OPTIONS
•
TA reels hold 1000 devices
•
TC reels hold 4000 devices
DRAFT ISSUE F - MAY 2004
1
SEMICONDUCTORS
ZXSC440
ABSOLUTE MAXIMUM RATINGS
PARAMETER LIMIT UNIT
V
CC
DRIVE -0.3 to V
READY -0.3 to V
CHARGE -0.3 to The lower of (+5.0) or (V
, SENSE -0.3 to The lower of (+5.0) or (VCC+0.3) V
V
FB
Operating temperature -40 to +85 °C
Storage temperature -55 to +150 °C
Power dissipation at 25°C 450 mW
-0.3 to +10 V
+ 0.3 V
CC
+ 0.3 V
CC
+0.3) V
CC
ELECTRICAL CHARACTERISTICS (Test conditions V
= 3V, T= 25°C unless otherwise stated)
CC
SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT
V
CC
Iq
I
STDN
Eff
Acc
TCO
T
DRV
F
OSC
(1)
(2)
REF
REF
VCCrange
Quiescent current VCC=8V 220 A
Shutdown current 4.5 A
Efficiency 85 %
Reference tolerance 1.8V < VCC< 8V -3.0 3.0 %
Reference temp co 0.005 %/°C
Discharge pulse width 1.8V < VCC< 8V 1.7 s
Operating frequency 200 kHz
1.8 8 V
INPUT PARAMETERS
V
SENSE
I
SENSE
V
FB
I
FB
VIH
(2)
(3)
Sense voltage 22 28 34 mV
Sense input current VFB=0V;V
=0V -1 -7 -15 A
SENSE
Feedback voltage 291 300 309 mV
Feedback input current VFB=0V;V
Shutdown threshold 1.5 V
=0V -1.2 -4.5 A
SENSE
CC
VIL Shutdown threshold 0 0.55 V
dV
LN
Line voltage regulation 0.5 %/V
OUTPUT PARAMETERS
I
DRIVE
V
DRIVE
C
DRIVE
VOH
VOL
T
READY
dI
LD
READY
READY
Transistor drive current V
Transistor voltage drive 0 VCC-0.4 V
Mosfet gate drive cpbty 300 pF
Ready flag output high I
Ready flag output low I
Load current regulation 0.01 %/mA
= 0.7V 2 3.4 5 mA
DRIVE
= -300nA, TA=25°C 2.5 V
EOR
=1mA,TA=25°C 0 1 V
EOR
CC
TA=25°C 195 s
V
V
NOTES
(1) Excluding gate/base drive current.
(2) IFBis typically half of these at 3V.
(3) Shutdown pin voltage must not exceed (VCC+0.3V) or 5V, whichever is lower.
SEMICONDUCTORS
2
DRAFT ISSUE F - MAY 2004
ZXSC440
ABSOLUTE MAXIMUM RATINGS
PIN # NAME DESCRIPTION
1 DRIVE Drive output for external switching transistor. Connect to base or gate of external
2V
3 SENSE Inductor current sense input. Internal threshold voltage set to 28mV. Connect
4 N/C
5 CHARGE Initiate photoflash capacitor charging
6 READY Signal to microprocessor when photoflash capacitor charged
7 GND Ground
8V
FB
CC
BLOCK DIAGRAM
switching transistor
Reference voltage. Internal threshold set to 300mV. Connect external resistor
network to set output voltage
external sense resistor
Supply voltage, 1.8V to 8V
DRAFT ISSUE F - MAY 2004
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SEMICONDUCTORS
ZXSC440
DEVICE DESCRIPTION
Bandgap reference
Allthresholdvoltages and internal currentsarederived
from a temperature compensated bandgap reference
circuit with a referencevoltage 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 = V
orgate of the externaltransistor.Inorder to operatethe
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
driveoutput. Normally theDRIVEoutput is"HIGH";the
external switching transistor is turned on. Current
ramps up in the inductor,the switchingtransistor and
external current sensing resistor. This voltage is
sensed by comparator, Comp2,at input SENSE. Once
the current sense voltage across the sensing resistor
exceeds28mV, comparator, Comp2, through gate U1,
triggers a re-triggerable monostableand turns off the
output drive stage for 1.7s. The inductor discharges
into the reservoir capacitor. After 1.7sa new charge
cycle begins, thus ramping the output voltage. When
the output voltage reachesthe nominal value andV
gets an input voltage of more than 300mV, the
monostable is forced "on" from Comp1 through gate
U1, until the feedbackvoltage fallsbelow 300mV. The
above action continues to maintain regulation, with
slight hysteresis on the feedback threshold.
-0.4V) drives the base
CC
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 V
voltage of less than 195s are ignored. If the output
voltage falls below the nominal value for more than
195s,outputREADY goes "LOW". Thiscan beused to
signal to the camera controller that the flash unit has
charged fully and is ready to use.
FB
). Short dips of the output
CC
SEMICONDUCTORS
DRAFT ISSUE F - MAY 2004
4
TYPICAL OPERATING CHARACTERISTICS
(For typical application circuit at V
=3V and TA=25 °C unless otherwise stated)
IN
ZXSC440
DRAFT ISSUE F - MAY 2004
5
SEMICONDUCTORS
ZXSC440
APPLICATIONS
Switching transistor selection
The choice of switching transistor has a major impact
ontheconverterefficiency.For optimum performance,
a bipolar transistor with low V
required.TheV
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
theMOSFETwill perform the same function,withjusta
small loss of efficiency.
oftheswitchingtransistorisalsoan
CEO
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:
V
R(DIODE)
= V
OUT(MAX)
+ (VINx TURNSRATIO)
and high gain is
CE(SAT)
Therefore,with a 300V output, a supplyof 8 voltsand a
1:12 step-up transformer, there will be a 396V across
the diode. This occurs during the current ramp-up in
theprimary, as ittransformsthe input voltageupbythe
turns ratio and the polarityat the secondary is such as
to
add
to the output voltage already being held off by
the diode.
Peak current definition
In general, theI
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
determined by:
R
SENSE
value must bechosen to ensurethat
PK
is decided the value of R
V
SENSE
=
I
PK
SENSE
can be
Sense resistor
A low value sense resistor is required to set the peak
current. Power in this resistor is negligible due to the
lowsensevoltage threshold, V
recommended sense resistors:
Manufacturer Series RDC( ) Range Size Tolerance URL
Cyntec RL1220 0.022 - 10 0805 ±5%
IRC LR1206 0.010 - 1.0 1206 ±5%
Usinga22m⍀ senseresistorresultsin a peak currentof
just over 1.2A.
.Belowis a table of
SENSE
http://www.cyntec.com
http://www.irctt.com
DRAFT ISSUE F - MAY 2004
SEMICONDUCTORS
6
Transformer parameters
Proprietary transformers are available, for example the
Pulse PAO367, Primary inductance: 24uH, Core: Pulse
PAO367, Turns ratio: 1:12, seeBill ofMaterials below. If
designing atransformer, 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 airgap tocope 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
T-15-089 6.4x7.7x4 12 400 10:2 211 27
T-15-083 8x8.9x2 20 500 10:2 675 35
L
PRI
(H)
L
PRI -LEAK
(nH)
NR
PRI
(m⍀)
R
Manufacturer
SEC
(⍀)
Tokyo Coil Eng.
www.tokyo-coil.co.jp
ZXSC440
SBL-5.6-1 5.6x8.5x4 10 200 10:2 103 26
PAO367 9.1x9.1x5.1 24 12:1
Kijima Musen
Kijimahk@netvigator.com
Pulse
www.pulseeng.com
DRAFT ISSUE F - MAY 2004
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SEMICONDUCTORS
ZXSC440
Output power calculation
Thisisapproximately the powerstoredinthe coil times
the frequency of operation times the efficiency.
Assuming a current of1.2 amps in a30µH primary, the
stored energy will be 21.6µJ. The frequency is set by
the time it takes theprimary toreach1.2 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
powerofabout1.6watts. With an efficiency of 75% the
output power will be 1.2 watts. An 80µF capacitor
chargedto 300 volts stores 3.6J, so1.2 watts willtake 3
seconds to charge it. Higherinput voltages reducethe
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:
V
= VFB(1 + RA / RB),
OUT
where V
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 I
V
pin. Output is adjustable from VFBto the (BR)V
FB
of the switching transistor, Q1.
Inpractice, there will be some stray capacitance across
RA and this will causea leadinthe 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.
=300mV
FB
FB(MAX)
=200nA to the
CEO
SEMICONDUCTORS
DRAFT ISSUE F - MAY 2004
8
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 inputloop, power-switchloop, rectifier loop
and output loop. The supply charging the input
capacitor forms theinput loop.The power-switch loop
isdefined when Q1 is 'on', currentflows from theinput
through the transformer primary, Q1, R
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.Theoutput loop is formed bytheoutputcapacitor
supplying the load when Q1 is switched back off.
SENSE
and to
ZXSC440
To optimize for best performance each of these loops
keptseparate from each other and interconnected with
short, thick traces thus minimizing parasitic
inductance, capacitance and resistance. Also the
R
resistor should be connected, with minimum
SENSE
trace length, between emitter lead of Q1 and ground,
again minimizing stray parasitics.
DRAFT ISSUE F - MAY 2004
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SEMICONDUCTORS
ZXSC440
REFERENCE DESIGNS
General camera photoflash charger
Circuit diagram
Specification
V
=5V
IN
V
= 275V
OUT
Efficiency = 71%
Charging time = 4 seconds
Bill of materials
Ref Value Package Part number Manufacturer Notes
U1 MSOP8 ZXSC440 Zetex
Q1 SOT23 ZXMN6A07F Zetex 60V N-channel MOSFET
(2)
D1
Tx1 Pulse See note
R1 22m⍀ 0805 RL1210 Cyntec
R2 10M⍀/400V Axial Generic Generic Output voltage across resistor
R3 10k⍀ 0805 Generic Generic
R4 100k⍀ 0805 Generic Generic
C1 100uF/10V 0805 Generic Murata
C2 10pF/500V 1206 Generic Generic Output voltage seen across capacitor
C3 10nF/6V3 1206 Generic Generic
C4 120uF/330V Radial FW Series Rubycon Photoflash capacitor
200V SOT23 BAS21 Philips x2 200V fast rectifier diodes
connected in series
(1)
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
High power digital camera photoflash charger
ZXSC440
Specification
V
=3V
IN
V
= 275V
OUT
Circuit diagram
Efficiency = 69%
Charging time = 5 seconds
Bill of materials
Ref Value Package Part number Manufacturer Notes
U1 MSOP8 ZXSC440 Zetex
U2 SOT23-6 ZXTD6717 Zetex NPN/PNP dual
Q1 SOT23 FMMT619 Zetex 50V NPN low sat
D1 200V SOT23 BAS21 Philips 200V fast rectifier
D2 200V SOT23 BAS21 Philips 200V fast rectifier
D3 2A SOT23-6 ZLLS2000 Zetex 2A Schottky diode
Tx1 PAO367 Pulse See note
R1 22m⍀ 0805 RL1210 Cyntec
R2 130⍀ 0805 Generic Generic
R3 2k2⍀ 0805 Generic Generic
R4 10M⍀/400V Axial Generic Generic Output voltage across resistor
R5 10k⍀ 0805 Generic Generic
C1 100uF/10V 0805 Generic Murata
C2 220nF 0805 GRM Series Murata
C3 10pF/500V 1206 Generic Generic Output voltage seen across capacitor
C4 10nF/6V3 1206 Generic Generic
C5 120uF/330V Radial FW Series Rubycon Photoflash capacitor
(1)
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
V
=3V
IN
V
= 275V
OUT
Circuit diagram
Efficiency = 58%
Charging time = 6.8 seconds
Bill of materials
Ref Value Package Part number Manufacturer Notes
U1 MSOP8 ZXSC440 Zetex
U2 SOT23-6 ZXTD6717 Zetex NPN/PNP dual
Q1 SOT23 FMMT619 Zetex 50V NPN low sat
D1 200V SOT23 BAS21 Philips 200V fast rectifier
D2 200V SOT23 BAS21 Philips 200V fast rectifier
D3 2A SOT23-6 ZLLS2000 Zetex 2A Schottky diode
Tx1 Sumida See note
R1 33m⍀ 0805 RL1210 Cyntec
R2 200⍀ 0805 Generic Generic
R3 2k2⍀ 0805 Generic Generic
R4 10M⍀/400V Axial Generic Generic Output voltage across resistor
R5 10k⍀ 0805 Generic Generic
C1 100uF/10V 0805 Generic Murata
C2 220nF 0805 GRM Series Murata
C3 10pF/500V 1206 Generic Generic Output voltage seen across capacitor
C4 10nF/6V3 1206 Generic Generic
C5 80uF/330V Radial FW Series Rubycon Photoflash capacitor
(1)
NOTES:
(1) Transformer specification: Primary inductance: 32uH, Core: Sumida CEEH64, Turns ratio: 1:10
SEMICONDUCTORS
12
DRAFT ISSUE F - MAY 2004
PACKAGE OUTLINE
ZXSC440
e
8
c
15%%D MAX
E
E1
R
GAGE PLANE
0.25
INDENT AREA
(D/2 X E1/2)
1
D
A
A2
A1
b
Controlling dimensions are in millimeters. Approximate conversions are given in inches
PACKAGE DIMENSIONS
DIM
Millimeters Inches
Min Max Min Max Min Max Min Max
DIM
A - 1.10 - 0.0433 E 4.90 BSC 0.025 BSC
A1 0.05 0.15 0.002 0.006 E1 2.90 3.10 0.114 0.122
A2 0.75 0.95 0.0295 0.0374 e 0.65 BSC 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 -
Millimeters Inches
R1
L
0%%D-6%%D
© Zetex plc 2004
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Zetex GmbH
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Germany
Telefon: (49) 89 45 49 49 0
Fax: (49) 89 45 49 49 49
europe.sales@zetex.com
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DRAFT ISSUE F - MAY 2004
13
SEMICONDUCTORS
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