DEMO CIRCUIT 988
LT3585EDDB-0/-1/-2/-3
QUICK START GUIDE
LT3585EDDB -0/-1/-2/-3
Photoflash Charger with Ad-
justable Input Current and
IGBT Driver
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
SYMBOL
V
BAT
V
IN
VOUT
TCHARGE
PARAMETER
VBAT Voltage Range
VIN Voltage Range
Output Voltage
Charge Time
Specifications are at TA = 25°
C
CONDITIONS
VIN = 2.8V – 4.2V
VBAT = 1.8V – 4.2V
VIN = 2.8V – 4.2V, VBAT = 1.8V – 4.2V
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
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
MIN
1.8
2.8
TYP
MAX
4.2
4.2
UNITS
V
V
V
mS
TCHAREG(R) Charge time (Reduced current)
320
468
600
1180
779
890
1237
2547
mS
1
LT3585EDDB-0/-1/-2/-3
PERFORMANCE SUMMARY
SYMBOL
PARAMETER
Specifications are at TA = 25°
C
CONDITIONS
LT3585-2, VBAT = 3.6V, CHRG/IADJ hi-Z
MIN
TYP
1550
MAX
UNITS
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.
2
LT3585EDDB-0/-1/-2/-3
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
3
LT3585EDDB-0/-1/-2/-3
Figure 1. Proper Measurement Equipment Setup
4
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