ZETEX ZXSC440 Technical data

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 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 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

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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

SEMICONDUCTORS

ZXSC440

ABSOLUTE MAXIMUM RATINGS

PARAMETER LIMIT UNIT

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

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

+ 0.3 V

+0.3) V

ELECTRICAL CHARACTERISTICS (Test conditions V

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

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT

Iq I

STDN

Eff Acc TCO T

DRV

OSC

(1)

(2)

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

SENSE

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

VIL Shutdown threshold 0 0.55 V dV

Line voltage regulation 0.5 %/V

OUTPUT PARAMETERS

DRIVE

VOH VOL T

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

TA=25°C 195 ␮s

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

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

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

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

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 ±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 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 1.7␮s. The inductor discharges into the reservoir capacitor. After 1.7␮sa 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

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 V voltage of less than 195␮s are ignored. If the output voltage falls below the nominal value for more than 195␮s,outputREADY goes "LOW". Thiscan beused to signal to the camera controller that the flash unit has charged fully and is ready to use.

). Short dips of the output

SEMICONDUCTORS

DRAFT ISSUE F - MAY 2004

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