FEATURES
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LT3420/LT3420-1
Photoflash Capacitor
Chargers with Automatic Refresh
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.
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.
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
APPLICATIO S
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Digital Camera Flash Unit
Film Camera Flash Unit
High Voltage Power Supplies
TYPICAL APPLICATIO
V
BAT
1.8V TO 6V
INPUT CURRENT
≈350mA
T1
1:12
C1
4.7µF
5,6
8
3,4
51.1k
2
V
CC
2.5V TO 10V
4
C2
4.7µF
9
8
V
BAT
V
CC
LT3420
CHARGE
DONE
C
T
10
0.1µF
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
R
REF
GND
5
1
3
R
FB
6
SW
SEC
320V
D1
V
BAT
1.8V TO 6V
INPUT CURRENT
≈450mA
1
2
C3
220µF
7
330V
PHOTOFLASH
CAPACITOR
3
R
FB
+
V
CC
2.5V TO 6V
CHARGE
DONE
CHARGE
DONE
2k
DANGER HIGH VOLTAGE
OPERATION BY HIGH VOLTAGE
TRAINED PERSONNEL ONLY
3420 F01
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
Figure 1. High Charge Rate LT3420 Photoflash Circuit
Figure 2. Small Size LT3420-1 Photoflash Circuit
3420fb
U
U
U
T1
1:10
(3mm TALL)
C1
4.7µF
4
5
D1
320V
3
60.4k
V
BAT
V
CC
LT3420-1
CHARGE
DONE
C
T
10
0.1µF
R
REF
GND
5
1
6
SW
SEC
6
4
C2
4.7µF
9
8
C3
100µF
7
330V
PHOTOFLASH
CAPACITOR
+
2k
3420 F02
1
LT3420/LT3420-1
ABSOLUTE
(Note 1)
AXI U RATI GS
DONE Voltage .......................................................... 16V
Current into DONE Pin ..........................................
±1mA
Maximum Junction Temperature .......................... 125°C
Operating Ambient Temperature Range
(Note 3) .............................................. – 40°C to 85°C
Storage Temperature Range ................. – 40°C to 125°C
Lead Temperature (Soldering, 10 sec)
(For MS Package only) ..................................... 300°C
V
CC
Voltage .............................................................. 16V
V
BAT
Voltage ............................................................ 16V
SW Voltage (Note 2)
LT3420 ................................................................ 38V
LT3420-1 ............................................................ 50V
SEC Current ......................................................
±200mA
R
FB
Current ...........................................................
±3mA
R
REF
Voltage ........................................................... 2.5V
CHARGE Voltage ...................................................... 16V
CT Voltage .............................................................. 1.5V
PACKAGE/ORDER INFORMATION
TOP VIEW
R
REF
V
BAT
R
FB
V
CC
GND
1
2
3
4
5
11
10 C
T
9 CHARGE
8 DONE
7 SEC
6 SW
ORDER PART
NUMBER
TOP VIEW
LT3420EDD
LT3420EDD-1
DD PART
MARKING
LBJW
LBJX
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 3°C/W
EXPOSED PAD IS GND (PIN 11)
AND MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
BAT
= 3.3V, V
CHARGE
= V
CC
unless otherwise noted. (Note 3)
PARAMETER
Minimum Operating Voltage, V
CC
Maximum Operating Voltage, V
CC
V
CC
UVLO Hysteresis
Minimum V
BAT
Voltage
Maximum V
BAT
Voltage
V
BAT
UVLO Hysteresis
R
REF
Threshold Voltage
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
●
R
REF
Pin Bias Current
Quiescent Current
Quiescent Current in Shutdown
V
RREF
= 0V, Switching
V
RFB
= V
BAT
– 0.2V (Note 4)
V
RREF
= 1.1V, Not Switching
V
CHARGE
= 0V, V
IN
= 3.3V
2
U
U
W
W W
U
W
ORDER PART
NUMBER
10
9
8
7
6
C
T
CHARGE
DONE
SEC
SW
R
REF
V
BAT
R
FB
V
CC
GND
1
2
3
4
5
LT3420EMS
LT3420EMS-1
MS PART MARKING
LTYH
LTAJG
MS PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 100°C/W,
θ
JC
= 45°C/W
(4-LAYER BOARD)
MIN
TYP
2.2
40
1.6
275
MAX
2.5
16
1.8
16
UNITS
V
V
mV
V
V
mV
V
V
µA
µA
µA
0.98
0.975
1.00
2
90
0.01
1.02
1.025
4
130
1
3420fb
LT3420/LT3420-1
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= V
BAT
= 3.3V, V
CHARGE
= V
CC
unless otherwise noted. (Note 3)
PARAMETER
Primary Side Current Limit
Secondary Side Current Limit
Leakage Blanking Pulse Width
Refresh Timer Charge/Discharge Current
Refresh Timer Upper Threshold
Refresh Timer Lower Threshold
Switch V
CESAT
Switch Leakage Current
CHARGE Input Voltage High
CHARGE Input Voltage Low
CHARGE Pin Bias Current
DONE Output Signal High
DONE Output Signal Low
V
CHARGE
= 3V
V
CHARGE
= 0V
100k from V
CC
to DONE
33µA into DONE Pin
4.5
0.01
3.3
100
200
LT3420, SW = 1A (Note 5)
LT3420-1, SW = 0.5A (Note 5)
V
SW
= 38V (LT3420), V
SW
= 50V (LT3420-1)
1.5
0.2
15
0.1
CONDITIONS
LT3420 (Note 5)
LT3420-1 (Note 5)
LT3420 (Note 5)
LT3420-1 (Note 5)
LT3420
LT3420-1
V
CT
= 0.75V
1.5
0.9
0.45
MIN
1.20
0.75
20
5
TYP
1.4
0.9
40
15
200
0
2.5
1.0
0.5
220
130
0.01
3.5
1.1
0.55
340
230
1
MAX
1.60
1.05
50
25
UNITS
A
A
mA
mA
ns
ns
µA
V
V
mV
mV
µA
V
V
µA
µA
V
mV
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Rated breakdown with LT3420 in power delivery mode and power
switch off.
Note 3:
The LT3420/LT3420-1 are guaranteed to meet performance
specifications from 0°C to 70°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 4:
Bias current flows out of R
FB
pin.
Note 5:
Current limit and V
CESAT
guaranteed by design and/or correlation
to static test for DD package.
TYPICAL PERFOR A CE CHARACTERISTICS
Graphs apply to both the LT3420 and LT3420-1 unless otherwise noted.
Output Voltage in Refresh Mode,
LT3420
335
330
325
320
V
OUT
(V)
V
OUT
(V)
TIME (s)
315
310
305
300
295
–50 –25
0
25
FIGURE 1 CIRCUIT
V
CC
= 3.3V
V
BAT
= 3.3V
50
75
100
125
TEMPERATURE (°C)
3420 G01
U W
Output Voltage in Refresh Mode,
LT3420
335
330
8
325
320
315
310
305
300
295
2.5
3.0
3.5
4.0
FIGURE 1 CIRCUIT
V
CC
= V
IN
V
BAT
= V
IN
T
A
= 25°C
4.5
5.0
5.5
6.0
V
IN
(V)
3420 G02
Charge Time, LT3420
10
FIGURE 1 CIRCUIT
UNLESS OTHERWISE
NOTED.
V
OUT
CHARGED
FROM
50V TO 320V
T
A
= 25°C
6
C
OUT
= 220µF
4
C
OUT
= 100µF
2
0
2
3
4
V
BAT
(V)
5
6
3420 G03
3420fb
3
LT3420/LT3420-1
TYPICAL PERFOR A CE CHARACTERISTICS
Graphs apply to both the LT3420 and LT3420-1 unless otherwise noted.
Output Voltage in Refresh Mode,
LT3420-1
335
330
325
320
V
OUT
(V)
V
OUT
(V)
TIME (s)
315
310
305
300
295
–50 –25
0
25
FIGURE 2 CIRCUIT
V
CC
= 3.3V
V
BAT
= 3.3V
50
75
100
125
TEMPERATURE (°C)
3420 G04
Charge Pin Input Current
10
T
A
= 25°C
8
CURRENT (µA)
CURRENT (mA)
CURRENT (A)
6
4
2
25
0
2
3
6
5
7
4
8
CHARGE PIN VOLTAGE (V)
9
10
Efficiency of Figure 1 Circuit,
LT3420
90
T
A
= 25°C
V
IN
= 5V
1.2
80
EFFICIENCY (%)
70
1.0
CURRENT (mA)
V
IN
= 3.3V
CURRENT (A)
60
50
V
CC
= V
BAT
= V
IN
40
50
100
150
250
200
V
OUT
(V)
300
350
3420 G10
4
U W
3420 G07
Output Voltage in Refresh Mode,
LT3420-1
335
330
325
320
315
310
305
300
295
2.5
3.0
3.5
4.0
FIGURE 2 CIRCUIT
V
CC
= V
IN
V
BAT
= V
IN
T
A
= 25°C
4.5
5.0
5.5
6.0
V
IN
(V)
3420 G05
Charge Time, LT3420-1
10
FIGURE 2 CIRCUIT
V
OUT
CHARGED
FROM 50V TO 320V
T
A
= 25°C
8
6
C
OUT
= 100µF
4
C
OUT
= 40µF
2
0
2
3
4
V
BAT
(V)
3420 G06
5
6
Primary Current Limit, LT3420
1.7
60
55
Secondary Current Limit, LT3420
1.5
50
45
40
35
30
1.3
1.1
0.9
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
20
–50 –25
0
25
50
75
100
125
TEMPERATURE (°C)
3420 G08
3420 G09
Primary Current Limit, LT3420-1
35
30
1.1
Secondary Current Limit, LT3420-1
25
20
15
10
0.9
0.8
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
5
–50 –25
0
25
50
75
100
125
TEMPERATURE (°C)
3420 G11
3420 G12
3420fb
LT3420/LT3420-1
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
T
A
= 25°C
AVERAGE INPUT CURRENT (mA)
80
V
IN
= 5V
V
IN
= 3.3V
900
AVERAGE INPUT CURRENT (mA)
EFFICIENCY (%)
70
60
50
V
CC
= V
BAT
= V
IN
100
150
250
200
V
OUT
(V)
300
350
3420 G13
40
50
Quiescent Current in Refresh Mode
140
T
A
= 25°C
QUIESCENT CURRENT (µA)
V
BAT
PIN VOLTAGE (V)
V
CC
PIN VOLTAGE (V)
120
100
80
60
2.5
4.0
5.5
7.0
V
CC
(V)
3420 G16
U W
8.5
10
Input Current, LT3420
1000
FIGURE 1 CIRCUIT
V
CC
= V
BAT
= 3.3V
T
A
= 25°C
600
550
500
450
400
350
300
Input Current, LT3420-1
FIGURE 2 CIRCUIT
V
CC
= V
BAT
= 3.3V
T
A
= 25°C
800
700
600
500
50
100
150
250
200
V
OUT
(V)
300
350
3420 G14
50
100
150
200
250
V
OUT
(V)
300
350
3420 G15
V
CC
Minimum Operating Voltage
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
–50 –25
0
25
50
75
100
125
V
–
V
+
ENABLE VOLTAGE
IS HYSTERETIC
2.0
V
BAT
Minimum Operating Voltage
ENABLE VOLTAGE
IS HYSTERETIC
V
+
1.6
V
–
1.8
1.4
1.2
1.0
–50 –25
0
25
50
75
100
125
TEMPERATURE (°C)
3420 G17
TEMPERATURE (°C)
3420 G18
3420fb
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