DC988A-A - ANALOG DEVICES - Datasheet.Directory

LT3585EDDB

DESCRIPTION

WARNING!

Do not look directly at flash.

This circuit produces light that can damage eyes.

WARNING!

Lethal voltages are present on the circuit

board.

Do not operate the assembly unless you are

trained to handle high voltage circuits

Demonstration circuit 988 is a Photoflash Charger

with Adjustable Input Current and IGBT Driver fea-

turing the LT3585EDDB-x family of products. It

demonstrates a complete xenon photoflash solu-

tion, including the photoflash capacitor, flash tube

and trigger circuit, along with an input current ad-

just capability. An on-board microcontroller gener-

ates the necessary signals to produce an on-

demand flash, red-eye sequence, and flash ca-

pacitor refresh.

The demonstration board comes in four variants.

DC988-A uses the LT3585EDD-0, while DC988-B,

DC988-C and DC988-D use the LT3585EDD-1,

LT3585EDD-2, LT3585EDD-3, respectively.

The LT3585-x are highly integrated devices de-

signed to charge photoflash capacitors in digital

and film cameras. Its unique control technique al-

lows for the use of extremely small transformers.

Each part contains an on-chip high voltage NPN

power switch. Output voltage detection is com-

pletely contained within the part, eliminating the

need for any discrete zener diodes or resistors for

high voltage output sensing. The output can be

adjusted by simply changing the turns ratio of the

transformer.

The CHRG/IADJ pin gives full control of the part to

the user. Driving CHRG/IADJ lows puts the part in

shutdown. The CHRG/IADJ pin can also be used

to reduce the current of the charger, useful in ex-

tending battery life. The DONE pin indicates when

the part has completed charging.

Design files for this circuit board are available.

Call the LTC factory.

, LTC, and LT are registered trademarks of Linear Technology Corporation.

PERFORMANCE SUMMARY

Specifications are at TA = 25°C

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

BAT

VBAT Voltage Range VIN = 2.8V – 4.2V

1.8 4.2

VIN Voltage Range VBAT = 1.8V – 4.2V 2.8 4.2

VOUT

Output Voltage VIN = 2.8V – 4.2V, VBAT = 1.8V – 4.2V

320

TCHARGE Charge Time

LT3585-3, VBAT = 3.6V, CHRG/IADJ high

LT3585-0, VBAT = 3.6V, CHRG/IADJ high

LT3585-1, VBAT = 3.6V, CHRG/IADJ high

LT3585-2, VBAT = 3.6V, CHRG/IADJ high

468

600

1180

779

TCHAREG(R)

Charge time (Reduced current)

LT3585-3, VBAT = 3.6V, CHRG/IADJ hi-Z

LT3585-0, VBAT = 3.6V, CHRG/IADJ hi-Z

LT3585-1, VBAT = 3.6V, CHRG/IADJ hi-Z

890

1237

2547

DEMO CIRCUIT

988

QUICK START GUIDE

LT3585EDDB -0/-1/-2/-

Photoflash Charger with A

justable Input Current and

IGBT Driver

LT3585EDDB

PERFORMANCE SUMMARY

Specifications are at TA = 25°C

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

LT3585-2, VBAT = 3.6V, CHRG/IADJ hi-Z

1550

QUICK START PROCEDURE

WARNING!

Do not look directly at flash.

This circuit produces light that can damage eyes.

WARNING!

Lethal voltages are present on the circuit

board.

Do not operate the assembly unless you are

trained to handle high voltage circuits

Demonstration circuit 988 is easy to set up to

evaluate the performance of the LT3585EDDB-x.

For proper measurement equipment setup and

test, refer to figure 1 and follow the procedure be-

low:

1. Set the jumper at JP1 across the DAT and

MCLR pins.

2. Set the jumper at JP2 to the HIGH CURRENT

position.

3. With the power supply disconnected from

DC988, set the VBAT voltage between 1.8V to

4.2V. Set the VIN voltage between 2.8V and

4.2V. Turn off the power supply.

4. Connect the power supply to DC988, referring

to the connection diagram given in figure 1.

5. Turn on the power supply, verifying that the

VIN and VBAT voltages are correctly set.

6. Press the ON/OFF button once. The

READY/CHARGE LED should glow red as the

LT3585 charges the output capacitor and then

glow green when it is done.

7. To flash the xenon tube, verify that the

READY/CHARGE LED is green. Avoid look-

ing directly at the xenon flash tube and press

the FLASH button once. After the tube

flashes, the READY/CHARGE LED should

turn red as the LT3585 replenishes the charge

in the flash capacitor.

8. To generate a red-eye sequence, verify that

the READY/CHARGE LED is green. Avoid

looking directly at the xenon flash tube and

press the REDEYE button once. After the

flash sequence is over, the READY/CHARGE

LED should turn red as the LT3585 replen-

ishes the charge in the flash capacitor.

9. When finished testing, press the ON/OFF

switch once. This flashes the xenon tube, dis-

charging the flash capacitor and shuts down

the LT3585. The output capacitor is not com-

pletely discharged when this operation is

complete. 50V or more may be left on the ca-

pacitor, so the user is cautioned to avoid

physical contact with the flash tube circuitry at

all times. The flash tube circuitry consists of

the secondary of T1, D1, C2, R3, R10, C3, T2,

FT1, and Q1.

10. If low current charging is desired, move the

jumper at JP2 to the LOW CURRENT position

and repeat steps 4-9 as necessary.

11. Monitor the DONE, CHARGE, and TRIGGER

signals by using the provided test points. Do

not make measurements from under the pro-

tective cover.

LT3585EDDB

OPERATION

The microcontroller has been programmed to scan

the interface button with a ½ second debounce

routine. You need to press and hold the buttons

down for at least ½ second in order for the micro-

controller to recognize a valid button event.

It is assumed that DC988 will be tested with power

provided from an external source, such as a lab

bench supply. Under such an operating condition,

the wire length between the DC988 board and the

power supply terminals can be several feet and

the line loss may be excessive. For this reason,

CIN has been added to the board at the input ter-

minals to attenuate the ground shifting associated

with pulling the main switch current through the

wires connecting to the power supply. This capaci-

tor would generally not be required in a battery

powered portable application, where the battery

would be physically located close to the LT3585

and the impedance of the connection is low.

The on-board microcontroller may be disabled by

removing the VIN and VBAT voltages and moving

the JP1 jumper to short the GND and CLK pins.

Apply power to the VIN and VBAT terminals and

press the ON/OFF button once. The

READY/CHARGE LED should blink red. The user

can now charge the output capacitor and activate

the flash tube by applying the appropriate signals

to the CHARGE and TRIGGER test points. The

timing can be validated by monitoring these and

the DONE signal. Please refer to the LT3585 data

sheet for detailed signal requirements.

The input current of an LT3585-x circuit can be re-

duced by changing the voltage of the CHRG/IADJ

pin. When this pin is driven high, the charge cycle

starts. If the CHRJ/IADJ pin is put into a high im-

pedance state (tri-state), the LT3585 will enter a

low charging current mode. For further details on

this function, please refer to the LT3585 data

sheet.

To enable the reduced charging current function

on the DC988 demo board, simply move the JP2

jumper the LOW CURRENT position before start-

ing the next output capacitor charge cycle. This

may be done while the DC988 board is still pow-

ered. With the jumper in this position, the micro-

controller will tri-state signal to the LT3585

CHRG/IADJ input shortly after driving the signal

high for a brief period.

WARNING!

Do not look directly at flash.

This circuit produces light that can damage eyes.

WARNING!

Lethal voltages are present on the circuit

board.

Do not operate the assembly unless you are

trained to handle high voltage circuits

LT3585EDDB

Figure 1.

Proper Measurement Equipment Setup

LT3585EDDB