LT3420 Datasheet, PDF (1/20 Pages) Linear Technology – Photoflash Capacitor Chargers with Automatic Refresh

LT3420/LT3420-1
Photoflash Capacitor
Chargers with Automatic Refresh
FEATURES
s _{Charges 220µF to 320V in 3.7 Seconds}
from 5V (LT3420)
s _{Charges 100µF to 320V in 3.5 Seconds}
from 5V (LT3420-1)
s _{Charges Any Size Photoflash Capacitor}
s _{Supports Operation from Two AA Cells or Any}
Supply from 1.8V to 16V
s _{Controlled Peak Switch Current: 1.4A (LT3420)}
1.0A (LT3420-1)
s _{Controlled Input Current: 840mA (LT3420)}
450mA (LT3420-1)
s _{Uses Standard Transformers}
s _{Efficient Flyback Operation (>75% Typical)}
s _{Adjustable Output}
s _{Automatic Refresh}
s _{Charge Complete Indicator}
s _{No High Voltage Zener Diode Required}
s _{No Output Voltage Divider Required}
s _{Small 10-Lead MSOP Package}
U
APPLICATIO S
s _{Digital Camera Flash Unit}
s _{Film Camera Flash Unit}
s _{High Voltage Power Supplies}
DESCRIPTIO
The LT^®3420/LT3420-1 charge high voltage photoflash
capacitors quickly and efficiently. Designed for use in both
digital and film cameras, these devices use a flyback
topology to achieve efficiencies up to four times better
than competing flash modules. A unique adaptive off-time
control algorithm* maintains current-limited continuous
mode transformer operation throughout the entire charge
cycle, eliminating the high inrush current often found in
modules.
The LT3420/LT3420-1 output voltage sensing scheme*
monitors the flyback voltage to indirectly regulate the
output voltage, eliminating an output resistor divider or
discrete zener diode. This feature allows the capacitor to
be held at a fully charged state without excessive power
consumption. Automatic refresh (which can be defeated)
allows the capacitor to remain charged while consuming
an average input current of about 2mA, at a user-defined
refresh rate. A logic high on the CHARGE pin initiates
charging, while the DONE pin signals that the capacitor is
fully charged.
, LTC and LT are registered trademarks of Linear Technology Corporation.
*U.S. Patent #6,518,733
TYPICAL APPLICATIO
V_BAT
1.8V TO 6V
C1
4.7µF
T1
1:12
5,6
8
D1
320V
DANGER HIGH VOLTAGE
3,4
1
OPERATION BY HIGH VOLTAGE
51.1k
TRAINED PERSONEL ONLY
23
6
V_CC
2.5V TO 10V
CHARGE
DONE
4
C2
4.7µF
V_BAT R_FB
V_CC
LT3420
SW
SEC
C3
7
220µF +
330V
PHOTOFLASH
CAPACITOR
9
CHARGE
8
DONE
1
R_REF
C_T
GND
10
0.1µF
5
2k
C1, C2: 4.7µF, X5R or X7R, 10V
C3: RUBYCON 220µF PHOTOFLASH CAPACITOR
T1: TDK SRW10EPC-U01H003 FLYBACK TRANSFORMER
D1: GENERAL SEMICONDUCTOR GSD2004S SOT-23
DUAL DIODE. DIODES CONNECTED IN SERIES
3420 F01
Figure 1. High Charge Rate LT3420 Photoflash Circuit
V_BAT
1.8V TO 6V
C1
4.7µF
T1
1:10
4
5
D1
320V
3
6
DANGER HIGH VOLTAGE
OPERATION BY HIGH VOLTAGE
60.4k
TRAINED PERSONEL ONLY
23
6
V_CC
2.5V TO 6V
CHARGE
DONE
V_BAT R_FB SW
4
C2
V_CC
SEC
4.7µF
LT3420-1
C3
7
100µF +
330V
PHOTOFLASH
CAPACITOR
9
CHARGE
8
DONE
1
R_REF
C_T
GND
10
0.1µF
5
2k
C1, C2: 4.7µF, X5R or X7R, 6.3V
C3: RUBYCON 100µF PHOTOFLASH CAPACITOR
T1: KIJIMA MUSEN SBL-5.6S-2
D1: GENERAL SEMICONDUCTOR GSD2004S SOT-23
DUAL DIODE. DIODES CONNECTED IN SERIES
3420 F02
Figure 2. Small Size LT3420-1 Photoflash Circuit
3420fa
1