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PDF LT3420-1 Data sheet ( Hoja de datos )
| Número de pieza | LT3420-1 | |
| Descripción | Photoflash Capacitor Chargers | |
| Fabricantes | Linear | |
| Logotipo |  |
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LT3420/LT3420-1
Photoflash Capacitor
Chargers with Automatic Refresh
FEATURES
DESCRIPTIO
■ Charges 220µF to 320V in 3.7 Seconds
from 5V (LT3420)
■ Charges 100µF to 320V in 3.5 Seconds
from 5V (LT3420-1)
■ Charges Any Size Photoflash Capacitor
■ Supports Operation from Two AA Cells or Any
Supply from 1.8V to 16V
■ Controlled Peak Switch Current: 1.4A (LT3420)
1.0A (LT3420-1)
■ Controlled Input Current: 840mA (LT3420)
450mA (LT3420-1)
■ Uses Standard Transformers
■ Efficient Flyback Operation (>75% Typical)
■ Adjustable Output
■ Automatic Refresh
■ Charge Complete Indicator
■ No High Voltage Zener Diode Required
■ No Output Voltage Divider Required
■ Small 10-Lead MSOP Package
■ Small 10-Lead (3mm × 3mm) DFN Package
U
APPLICATIO S
■ Digital Camera Flash Unit
■ Film Camera Flash Unit
■ High Voltage Power Supplies
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.
The LT3420/LT3420-1 are available in 10-Lead MSOP and
(3mm × 3mm) DFN packages.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. *Protected by U.S. Patents
including 6518733.
TYPICAL APPLICATIO
VBAT
1.8V TO 6V
INPUT CURRENT
≈350mA
C1
4.7µF
T1
1:12
5,6 8
D1
320V
3,4 1
51.1k
VCC
2.5V TO 10V
CHARGE
DONE
23
6
4
C2
4.7µF
VBAT RFB
VCC
LT3420
SW
SEC
C3
7
220µF +
330V
PHOTOFLASH
CAPACITOR
9
CHARGE
8
DONE
1
RREF
CT 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: VISHAY GSD2004S SOT-23
DUAL DIODE. DIODES CONNECTED IN SERIES
3420 F01
DANGER HIGH VOLTAGE
OPERATION BY HIGH VOLTAGE
TRAINED PERSONNEL ONLY
Figure 1. High Charge Rate LT3420 Photoflash Circuit
VBAT
1.8V TO 6V
INPUT CURRENT
≈450mA
C1
4.7µF
T1
1:10
(3mm TALL)
45
D1
320V
36
60.4k
VCC
2.5V TO 6V
CHARGE
DONE
23
6
VBAT RFB
4
C2 VCC
SW
SEC
4.7µF
LT3420-1
C3
7
100µF +
330V
PHOTOFLASH
CAPACITOR
9
CHARGE
8
DONE
1
RREF
CT 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: VISHAY GSD2004S SOT-23
DUAL DIODE. DIODES CONNECTED IN SERIES
3420 F02
Figure 2. Small Size LT3420-1 Photoflash Circuit
3420fb
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
Graphs apply to both the LT3420 and LT3420-1 unless otherwise noted.
Efficiency for Figure 2 Circuit,
LT3420-1
90
TA = 25°C
80 VIN = 5V
70 VIN = 3.3V
60
50
40 VCC = VBAT = VIN
50 100 150 200 250 300 350
VOUT (V)
3420 G13
Quiescent Current in Refresh Mode
140
TA = 25°C
120
100
80
60
2.5 4.0 5.5 7.0 8.5
10
VCC (V)
3420 G16
Input Current, LT3420
1000
900
FIGURE 1 CIRCUIT
VCC = VBAT = 3.3V
TA = 25°C
800
700
600
500
50 100 150 200 250 300 350
VOUT (V)
3420 G14
VCC Minimum Operating Voltage
2.6
ENABLE VOLTAGE
2.5 IS HYSTERETIC
2.4
2.3
2.2
2.1 V– V+
2.0
1.9
1.8
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3420 G17
LT3420/LT3420-1
Input Current, LT3420-1
600
FIGURE 2 CIRCUIT
VCC = VBAT = 3.3V
550 TA = 25°C
500
450
400
350
300
50
100 150 200 250
VOUT (V)
300 350
3420 G15
VBAT Minimum Operating Voltage
2.0
ENABLE VOLTAGE
IS HYSTERETIC
1.8
V+
1.6
1.4 V–
1.2
1.0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3420 G18
3420fb
5
5 Page 
LT3420/LT3420-1
APPLICATIO S I FOR ATIO
must be taken into account for the dynamic blocking
voltage capabilities of the LT3420/LT3420-1. The dynamic
blocking voltage capability of both parts is 38V.
Table 1 summarizes the various breakdown voltages of the
SW pin for both parts.
Table 1. SW Pin Voltage Ratings
PART
SW PIN DC RATING
LT3420
38V
LT3420-1
50V
SW PIN DYNAMIC RATING
38V
38V
Figure 7 shows what to examine in a new transformer
design to determine if the specifications for the SW pin are
met.
The first leakage inductance spike labeled “A” must not
exceed the dynamic rating of the SW pin. If it does exceed
the rating, then the transformer leakage inductance must
be lowered. The flyback waveform after the initial spike
labeled “B” must not exceed the DC rating of the SW pin.
If it does exceed the rating, then the turns ratio of the
transformer must be lowered. In measuring the voltage on
the SW pin, care must be taken in minimizing the ground
loop of the voltage probe. Careless probing will result in
inaccurate readings.
Note also the magnitude of the initial current spike in the
primary of the transformer labeled “C” when the power
switch turns on. If the leakage inductance is lowered to a
very low level, the internal capacitances of the transformer
will be high. This will result in the initial spike of current in
the primary becoming excessively high. The level of “C”
should be kept to 4A or less in a typical design for both the
LT3420 and LT3420-1. Please note that by inserting a loop
of wire in the primary to measure the primary current, the
leakage inductance of the primary will be made artificially
high. This may result in erroneous voltage measurements
on the SW pin.
The measurements shown in Figure 7 should be made
with both VOUT and VBAT at the maximum levels for the
given application. This results in the highest voltage and
current stress on the SW pin.
Transformer Secondary Capacitance
The total capacitance of the secondary should be mini-
mized for both efficient and proper operation of the LT3420/
LT3420-1. Since the secondary of the transformer under-
goes large voltage swings (approaching 600VP-P), any
capacitance on the secondary can severely affect the
MUST BE LESS THAN 4A
FOR BOTH THE LT3420
“C” AND LT3420-1
IPRI
0A
MUST BE LESS THAN 38V
FOR THE LT3420
“B” MUST BE LESS THAN 50V
FOR THE LT3420-1
“A”
VSW
MUST BE LESS THAN 38V
FOR BOTH THE LT3420
AND LT3420-1
0V
3420 F07
Figure 7. New Transformer Design Check (Not to Scale)
3420fb
11
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| PDF Descargar | [ Datasheet LT3420-1.PDF ] | |
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