QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 855
PHOTOFLASH CHARGER
1
LT3484EDCB-0/LT3484EDCB-1/LT3484EDCB-2
DESCRIPTION
Demonstration circuit 855 is a Photoflash Charger fea-
turing the LT3484EDCB-0, LT3484EDCB-1, and
LT3484EDCB-2. It demonstrates a complete photoflash
application, including the photoflash capacitor, flash
tube and trigger circuit. An on-board microcontrolller
generates the necessary signals to produce an on-
demand flash, red-eye sequence, and flash capacitor
refresh.
The demonstration board comes in three variants.
DC855A-A uses the LT3484EDCB-0, while DC855A-B
and DC855A-C use the LT3484EDCB-1 and
LT3484EDCB-2, respectively.
The LT3484 family of photoflash capacitor ICs is de-
signed for use in a digital camera and mobile phone ap-
plications where space is a premium. The LT3484’s pat-
ented control technique allows it to use extremely small
transformers, and the improved NPN power switch re-
quires no external Schottky diode clamp, reducing the
solution size. The output voltage detection requires no
external circuitry as the transformer turns ratio deter-
mines the final charger voltage.
The device features a V
BAT
pin, which allows the use of 2
alkaline cells to charge the capacitor. The CHARGE pin
gives full control of the part to the user. Driving
CHARGE low shuts the part down.
WARNING! Lethal voltages are present on the DC855
circuit board. Do not operate the assembly unless you
are trained to handle high voltage circuits.
Design files for this circuit board are available. Call
the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Table 1.
Performance Summary (T
A
= 25°C)
PARAMETER CONDITION VALUE
Minimum V
BAT
Voltage V
IN
= 2.8V – 4.2V 1.8VDC
Maximum V
BAT
Voltage V
IN
= 2.8V – 4.2V 4.2VDC
Minimum V
IN
Voltage V
BAT
= 1.8V – 4.2V 2.8VDC
Maximum V
IN
Voltage V
BAT
= 1.8V – 4.2V 4.2VDC
Output Voltage V
IN
= 2.8V – 4.2V, V
BAT
= 1.8V – 4.2V 320VDC, typical
Average input current
DC855A-A, LT3484-0
DC855A-C, LT3484-2
DC855A-B, LT3484-1
500mA, typical
350mA, typical
225mA, typical
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 855
PHOTOFLASH CHARGER
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OPERATING PRINCIPLES
The theory of operation of the LT3484 and xenon flash tube illumination has been discussed at length in the LT3484
data sheet and the Linear Technology Application Note AN95, respectively. The reader is referred to these documents,
available online at http://www.linear.com.
QUICK START PROCEDURE
WARNING! Lethal voltages are present on the DC855
circuit board. Do not operate the assembly unless you
are trained to handle high voltage circuits.
Demonstration circuit 855 is easy to set up to evaluate
the performance of the LT3484EDCB-0, LT3484EDCB-1,
and LT3484EDCB-2. Refer to Figure 1 for proper meas-
urement equipment setup and follow the procedure be-
low:
1.
Set the jumper at JP1 across the DAT and MCLR
pins.
2.
With the power supply disconnected from DC855,
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.
3.
Connect the power supply to DC855, referring to
the connection diagram given in Figure 1.
4.
Turn on the power supply, verifying that the VIN and
VBAT voltages are correctly set.
5.
Press the ON/OFF button once. The
READY/CHARGE LED should glow red while charg-
ing the output capacitor and then glow green.
6.
To flash the xenon tube, verify that the
READY/CHARGE LED is green. Avoid looking di-
rectly at the xenon flash tube and press the FLASH
button once. After the tube flashes, the
READY/CHARGE LED should turn red as the LT3484
replenishes the charge in the flash capacitor.
7.
To generate a red-eye sequence, verify that the
READY/CHARGE LED is green. Avoid looking di-
rectly 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 LT3484
replenishes the charge in the flash capacitor.
8.
When finished testing, press the ON/OFF switch
once. This flashes the xenon tube, discharging the
flash capacitor and shuts down the LT3484. The
output capacitor is not completely discharge when
this operation is complete. 50V or more may be left
on the capacitor, so the user is cautioned to avoid
physical contact with the flash tube circuitry at all
times. The flash tube circuitry consists of D1, C2,
R3, R10, C3, T2, FT1, and Q1.
9.
Monitor the DONE, CHARGE and TRIGGER bits by
using the provided test points. Do not make meas-
urements from under the protective cover.
10.
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. The
user can 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 LT3484 data sheet for de-
tailed signal requirements.
ADDITIONAL NOTES
It is assumed that DC855A will be tested with power
provided from an external source, such as a lab bench
supply. Under such an operating condition, the wire
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 855
PHOTOFLASH CHARGER
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length between the DC855A 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 terminals to attenuate the ground
shifting associated with pulling the main switch current
through the wires connecting to the power supply. This
capacitor would generally not be required in a battery
powered portable application, where the battery would
be physically located close to the LT3484 and the im-
pedance of the connection is low.
The flashtube for this reference design is a FTA160709,
manufactured by Perkin-Elmer. They can be contacted
at:
PerkinElmer Optoelectronics
Lithography and Lighting
1300 Optical Drive
Azusa, CA. 91702
Figure 1.
Proper Measurement Equipment Setup
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 855
PHOTOFLASH CHARGER
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