QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 895
PHOTOFLASH CHARGER WITH OUTPUT VOLTAGE MONITOR AND INTEGRATED IGBT
DRIVE
1
LT3485EDD-0/-1/-2/-3
DESCRIPTION
Demonstration circuit 895 is a Photoflash Charger with
Output Voltage Monitor and Integrated IGBT Drive, fea-
turing the LT3485EDD-x family of products. It demon-
strates a complete photoflash application, including the
photoflash capacitor, flash tube and trigger circuit. An
on-board microcontroller generates the necessary sig-
nals to produce an on-demand flash, red-eye sequence,
and flash capacitor refresh.
The demonstration board comes in four variants.
DC895A-A uses the LT3485EDD-0, while DC895A-B,
DC895A-C and DC895A-D use the LT3485EDD-1,
LT3485EDD-2, LT3485EDD-3, respectively.
The LT3485 family of photoflash capacitor ICs is de-
signed for use in digital camera and mobile phone appli-
cations where space is a premium. The LT3485’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. The LT3485 also in-
cludes a output voltage monitor, which generates an
analog signal proportional to the output, and an inte-
grated IGBT drive.
WARNING! Lethal voltages are present on the DC895
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
DC895A-D, LT3485EDD-3
DC895A-A, LT3485EDD-0
DC895A-C, LT3485EDD-2
DC895A-B, LT3485EDD-1
750mA, typical
500mA, typical
350mA, typical
225mA, typical
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 895
PHOTOFLASH CHARGER WITH OUTPUT VOLTAGE MONITOR AND INTEGRATED IGBT
DRIVE
2
OPERATING PRINCIPLES
The theory of operation of the LT3485 and xenon flash tube illumination has been discussed at length in the LT3485
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 DC895
circuit board. Do not operate the assembly unless you
are trained to handle high voltage circuits.
Demonstration circuit 895 is easy to set up to evaluate
the performance of the LT3485EDCB-x. Refer to
Figure 1 for proper measurement equipment setup and
follow the procedure below:
1.
Set the jumper at JP1 across the DAT and MCLR
pins.
2.
With the power supply disconnected from DC895,
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 DC895, 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 as the
LT3485 charges 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 LT3485
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 LT3485
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 LT3485. The
output capacitor is not completely discharged 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, VOUTMONT and
TRIGGER signals by using the provided test points.
Do not make measurements from under the protec-
tive 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 LT3485 data sheet for de-
tailed signal requirements.
ADDITIONAL NOTES
It is assumed that DC895A will be tested with power
provided from an external source, such as a lab bench
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 895
PHOTOFLASH CHARGER WITH OUTPUT VOLTAGE MONITOR AND INTEGRATED IGBT
DRIVE
3
supply. Under such an operating condition, the wire
length between the DC895A 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 LT3485 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 895
PHOTOFLASH CHARGER WITH OUTPUT VOLTAGE MONITOR AND INTEGRATED IGBT
DRIVE
4
