S E M I C O N D U C T O R S

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.

FEATURES

Charges a 80 F 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 4.5 A when not charging

Small MSOP8 low profile package

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.

APPLICATIONS

Digital camera flash unit

Film camera flash unit

ZXSC440

DRAFT ISSUE F - MAY 2004

PHOTOFLASH CHARGER

PINOUT

MSOP8 pin TOP VIEW

TYPICAL APPLICATION CIRCUIT

DEVICE

DEVICE DESCRIPTION

TEMPERATURE RANGE

PART

MARK

TAPING

OPTIONS

ZXSC440X8TA

Camera flash charger

-40°C to +85°C

ZXSC440

TA, TC

ZXSC440X8TC

ORDERING INFORMATION

TA reels hold 1000 devices

TC reels hold 4000 devices

ZXSC440

S E M I C O N D U C T O R S

DRAFT ISSUE F - MAY 2004

PARAMETER

LIMIT

UNIT

-0.3 to +10

DRIVE

-0.3 to V

+ 0.3

READY

-0.3 to V

+ 0.3

CHARGE

-0.3 to The lower of (+5.0) or (V

+0.3)

, SENSE

-0.3 to The lower of (+5.0) or (V

+0.3)

Operating temperature

-40 to +85

°C

Storage temperature

-55 to +150

°C

Power dissipation at 25°C

450

ABSOLUTE MAXIMUM RATINGS

SYMBOL

PARAMETER

CONDITIONS

MIN.

TYP.

MAX.

UNIT

range

1.8

(1)

Quiescent current

=8V

220

STDN

Shutdown current

4.5

Eff

(2)

Efficiency

Acc

REF

Reference tolerance

1.8V < V

< 8V

-3.0

3.0

TCO

REF

Reference temp co

0.005

%/°C

DRV

Discharge pulse width

1.8V < V

< 8V

1.7

OSC

Operating frequency

200

kHz

INPUT PARAMETERS

SENSE

Sense voltage

SENSE

Sense input current

=0V;V

SENSE

=0V

-1

-7

-15

Feedback voltage

291

300

309

(2)

Feedback input current

=0V;V

SENSE

=0V

-1.2

-4.5

VIH

(3)

Shutdown threshold

1.5

VIL

Shutdown threshold

0.55

Line voltage regulation

0.5

%/V

OUTPUT PARAMETERS

DRIVE

Transistor drive current

DRIVE

= 0.7V

3.4

DRIVE

Transistor voltage drive

-0.4

DRIVE

Mosfet gate drive cpbty

300

VOH

READY

Ready flag output high

EOR

= -300nA, T

=25°C

2.5

VOL

READY

Ready flag output low

EOR

= 1mA, T

=25°C

READY

=25°C

195

Load current regulation

0.01

%/mA

ELECTRICAL CHARACTERISTICS

(Test conditions V

= 3V, T= 25°C unless otherwise stated)

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.

ZXSC440

S E M I C O N D U C T O R S

DRAFT ISSUE F - MAY 2004

BLOCK DIAGRAM

PIN #

NAME

DESCRIPTION

DRIVE

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

SENSE

Inductor current sense input. Internal threshold voltage set to 28mV. Connect
external sense resistor

N/C

CHARGE

Initiate photoflash capacitor charging

READY

Signal to microprocessor when photoflash capacitor charged

GND

Ground

Supply voltage, 1.8V to 8V

ABSOLUTE MAXIMUM RATINGS

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 = V

-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 V

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

T h e R E A D Y c i r c u i t i s a r e - t r i g g e r a b l e 1 9 5 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 V

). 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.

ZXSC440

S E M I C O N D U C T O R S

DRAFT ISSUE F - MAY 2004

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 V

CE(SAT)

and high gain is

required. The V

CEO

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

TM 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:

R(DIODE)

= V

OUT(MAX)

+ (V

x T

URNS

ATIO

)

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:

Using a 22m

sense resistor results in a peak current of

just over 1.2A.

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 I

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

is decided the value of R

SENSE

can be

determined by:

SENSE

ZXSC440

S E M I C O N D U C T O R S

DRAFT ISSUE F - MAY 2004

Manufacturer

Series

(

) 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

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

S E M I C O N D U C T O R S

DRAFT ISSUE F - MAY 2004

Part No.

Size

(WxLxH) mm

PRI

( H)

PRI -LEAK

(nH)

PRI

(m )

SEC

( )

Manufacturer

T-15-089

6.4x7.7x4

400

10:2

211

Tokyo Coil Eng.
www.tokyo-coil.co.jp

T-15-083

8x8.9x2

500

10:2

675

SBL-5.6-1

5.6x8.5x4

200

10:2

103

Kijima Musen
Kijimahk@netvigator.com

PAO367

9.1x9.1x5.1

12:1

Pulse
www.pulseeng.com

ZXSC440 Transformer specifications

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.

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:

OUT

= V

(1 + RA / RB),

where V

=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 I

FB(MAX)

=200nA to the

pin. Output is adjustable from V

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.

ZXSC440

S E M I C O N D U C T O R S

DRAFT ISSUE F - MAY 2004

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, 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.

ZXSC440

S E M I C O N D U C T O R S

DRAFT ISSUE F - MAY 2004

REFERENCE DESIGNS

General camera photoflash charger

Specification

OUT

275V

Efficiency =

71%

Charging time =

4 seconds

ZXSC440

S E M I C O N D U C T O R S

DRAFT ISSUE F - MAY 2004

Circuit diagram

Ref

Value

Package

Part number

Manufacturer

Notes

MSOP8

ZXSC440

Zetex

SOT23

ZXMN6A07F

Zetex

60V N-channel MOSFET

(2)

200V

SOT23

BAS21

Philips

x2 200V fast rectifier diodes
connected in series

Tx1

Pulse

See note

(1)

22m

0805

RL1210

Cyntec

10M /400V

Axial

Generic

Output voltage across resistor

10k

0805

Generic

100k

0805

Generic

100uF/10V

0805

Generic

Murata

10pF/500V

1206

Generic

Output voltage seen across capacitor

10nF/6V3

1206

Generic

120uF/330V

Radial

FW Series

Rubycon

Photoflash capacitor

Bill of materials

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.

High power digital camera photoflash charger

Specification

OUT

275V

Efficiency =

69%

Charging time =

5 seconds

ZXSC440

S E M I C O N D U C T O R S

DRAFT ISSUE F - MAY 2004

Circuit diagram

Ref

Value

Package

Part number

Manufacturer

Notes

MSOP8

ZXSC440

Zetex

SOT23-6

ZXTD6717

Zetex

NPN/PNP dual

SOT23

FMMT619

Zetex

50V NPN low sat

200V

SOT23

BAS21

Philips

200V fast rectifier

200V

SOT23

BAS21

Philips

200V fast rectifier

SOT23-6

ZLLS2000

Zetex

2A Schottky diode

Tx1

PAO367

Pulse

See note

(1)

22m

0805

RL1210

Cyntec

130

0805

Generic

2k2

0805

Generic

10M /400V

Axial

Generic

Output voltage across resistor

10k

0805

Generic

100uF/10V

0805

Generic

Murata

220nF

0805

GRM Series

Murata

10pF/500V

1206

Generic

Output voltage seen across capacitor

10nF/6V3

1206

Generic

120uF/330V

Radial

FW Series

Rubycon

Photoflash capacitor

Bill of materials

NOTES:

(1) Transformer specification: Primary inductance: 24uH, Core: Pulse PAO367, Turns ratio: 1:12

Low power digital camera photoflash charger

Specification

OUT

275V

Efficiency =

58%

Charging time =

6.8 seconds

ZXSC440

S E M I C O N D U C T O R S

DRAFT ISSUE F - MAY 2004

Circuit diagram

Ref

Value

Package

Part number

Manufacturer

Notes

MSOP8

ZXSC440

Zetex

SOT23-6

ZXTD6717

Zetex

NPN/PNP dual

SOT23

FMMT619

Zetex

50V NPN low sat

200V

SOT23

BAS21

Philips

200V fast rectifier

200V

SOT23

BAS21

Philips

200V fast rectifier

SOT23-6

ZLLS2000

Zetex

2A Schottky diode

Tx1

Sumida

See note

(1)

33m

0805

RL1210

Cyntec

200

0805

Generic

2k2

0805

Generic

10M /400V

Axial

Generic

Output voltage across resistor

10k

0805

Generic

100uF/10V

0805

Generic

Murata

220nF

0805

GRM Series

Murata

10pF/500V

1206

Generic

Output voltage seen across capacitor

10nF/6V3

1206

Generic

80uF/330V

Radial

FW Series

Rubycon

Photoflash capacitor

Bill of materials

NOTES:

(1) Transformer specification: Primary inductance: 32uH, Core: Sumida CEEH64, Turns ratio: 1:10

ZXSC440

S E M I C O N D U C T O R S

DRAFT ISSUE F - MAY 2004

Europe

Zetex GmbH
Streitfeldstraße 19
D-81673 München
Germany

Telefon: (49) 89 45 49 49 0
Fax: (49) 89 45 49 49 49
europe.sales@zetex.com

Americas

Zetex Inc
700 Veterans Memorial Hwy
Hauppauge, NY 11788
USA

Telephone: (1) 631 360 2222
Fax: (1) 631 360 8222
usa.sales@zetex.com

Asia Pacific

Zetex (Asia) Ltd
3701-04 Metroplaza Tower 1
Hing Fong Road, Kwai Fong
Hong Kong

Telephone: (852) 26100 611
Fax: (852) 24250 494
asia.sales@zetex.com

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

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

DIM

Millimeters

Inches

DIM

Millimeters

Inches

Min

Max

Min

Max

Min

Max

Min

Max

1.10

0.0433

4.90 BSC

0.025 BSC

0.05

0.15

0.002

0.006

2.90

3.10

0.114

0.122

0.75

0.95

0.0295

0.0374

0.65 BSC

0.193 BSC

0.25

0.40

0.010

0.0157

0.40

0.70

0.0157

0.0192

0.13

0.23

0.005

0.009

0.07

0.0027

PACKAGE DIMENSIONS

Controlling dimensions are in millimeters. Approximate conversions are given in inches

0.25

15%%D MAX

GAGE PLANE

INDENT AREA
(D/2 X E1/2)

0%%D-6%%D

PACKAGE OUTLINE

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