LT3485EDD-3#PBF Linear Technology, LT3485EDD-3#PBF Datasheet - Page 12

• Manufacturer Part Number: LT3485EDD-3#PBF
• Description: IC CHARGER PHOTOFLASH 10-DFN
• Manufacturer: Linear Technology

Specifications of LT3485EDD-3#PBF

• Applications: Photoflash Capacitor Charger, Xenon
• Current - Supply: 5mA
• Voltage - Supply: 1.7 V ~ 10 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
LT3485-0/LT3485-1/
LT3485-2/LT3485-3
The peak current of the diode is simply:
For the circuit of Figure 8 with V
and I
is recommended for most LT3485-0/LT3485-1/LT3485-
2/LT3485-3 applications. Another option is to use the
BAV23S dual silicon diodes. Table 3 shows the various
diodes and relevant specifications. Use the appropriate
number of diodes to achieve the necessary reverse break-
down voltage.
Table 3. Recommended Output Diodes
PART
GSD2004S
(Dual Diode)
BAV23S
(Dual Diode)
MMBD3004S
(Dual Diode)
12
I
I
I
I
PK-SEC
PK-SEC
PK-SEC
PK-SEC
PK-SEC
=
=
=
=
N
1.4
N
2
0.7
is 137mA. The GSD2004S dual silicon diode
1
MAX REVERSE VOLTAGE
N
N
(
(
LT3485-3
LT3485-2
(
(
LT3485-0
LT3485-
U
1 TO 2 Li-Ion
2x300
2x250
2x350
V
5V
CC
(V)
2 AA OR
V
BAT
U
)
)
1 1
0.22µF
)
) )
BAT
4.7µF
MAX FORWARD CONTINUOUS CURRENT
DONE
CHARGE
V
IGBTPWR
IGBTIN
W
V
of 5V, V
IN
BAT
LT3485-0
IGBTOUT
V
PK-R
MONT
SW
Figure 5. Complete Xenon Circuit
GND
U
1
2
(mA)
225
225
225
is 371V
1:10.2
•
•
TO
MICRO
4
5
IGBT Drive
The IGBT is a high current switch for the 100A+ current
through the photoflash lamp. To create a redeye effect or
to adjust the light output, the lamp current needs to be
stopped, or quenched, with an IGBT before discharging
the photoflash capacitor fully. The IGBT device also con-
trols the 4kV trigger pulse required to ionize the xenon gas
in the photoflash lamp. Figure 5 is a schematic of a fully
functional photoflash application with the LT3485 serving
as the IGBT drive. An IGBT drive charges the gate capaci-
tance to start the flash. The IGBT drive does not need to
pull-up the gate fast because of the inherently slow nature
of the IGBT. A rise time of 2µs is sufficient to charge the
gate of the IGBT and create a trigger pulse. With slower
rise times, the trigger circuitry will not have a fast enough
edge to create the required 4kV pulse. The fall time of the
IGBT drive is critical to the safe operation of the IGBT. The
IGBT gate is a network of resistors and capacitors, as
shown in Figure 6. When the gate terminal is pulled low,
150µF
PHOTOFLASH
CAPACITOR
320V
CAPACITANCE
(pF)
1M
5
5
5
1
2
2.2µF
600V
TRIGGER
3
3485 F05
T
IGBT
C
A
FLASHLAMP
Philips Semiconductor
www.philips.com
www.diodes.com
www.vishay.com
[phone]
[phone]
[phone]
Diodes Inc
VENDOR
Vishay
34850123fb