LT3468/LT3468-1/LT3468-2
1
346812fa
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
■
Digital / Film Camera Flash
■
PDA / Cell Phone Flash
■
Emergency Strobe
■
Highly Integrated IC Reduces Solution Size
■
Uses Small Transformers:
5.8mm × 5.8mm × 3mm
■
Fast Photoflash Charge Times:
4.6s for LT3468 (0V to 320V, 100µF, V
IN
= 3.6V)
5.7s for LT3468-2 (0V to 320V, 100µF, V
IN
= 3.6V)
5.5s for LT3468-1 (0V to 320V, 50µF, V
IN
= 3.6V)
■
Controlled Input Current:
500mA (LT3468)
375mA (LT3468-2)
225mA (LT3468-1)
■
Supports Operation from Single Li-Ion Cell, or Any
Supply from 2.5V up to 16V
■
Adjustable Output Voltage
■
No Output Voltage Divider Needed
■
Charges Any Size Photoflash Capacitor
■
Low Profile (<1mm) SOT-23 Package
Photoflash Capacitor
Chargers in ThinSOT
TM
The LT
®
3468/LT3468-1/LT3468-2 are highly integrated
ICs designed to charge photoflash capacitors in digital and
film cameras. A patented control technique* allows for the
use of extremely small transformers. Each device contains
an on-chip high voltage NPN power switch. Output voltage
detection* is completely contained within the device,
eliminating the need for any discrete zener diodes or
resistors. The output voltage can be adjusted by simply
changing the turns ratio of the transformer. The LT3468
has a primary current limit of 1.4A, the LT3468-2 has a 1A
limit, and the LT3468-1 has a 0.7A limit. These different
current limit levels result in well controlled input currents
of 500mA for the LT3468, 375mA for the LT3468-2 and
225mA for the LT3468-1. Aside from the differing current
limit, the three devices are otherwise equivalent.
The CHARGE pin gives full control of the part to the user.
Driving CHARGE low puts the part in shutdown. The DONE
pin indicates when the part has completed charging. The
LT3468 series of parts are available in tiny low profile
(1mm) SOT-23 packages.
DANGER HIGH VOLTAGE – OPERATION BY HIGH VOLTAGE
TRAINED PERSONNEL ONLY
LT3468 Photoflash Charger Uses
High Efficiency 4mm Tall Transformer
LT3468
CHARGE
GND
V
IN
SW
+
DONE DONE
CHARGE
4.7µF
100k
1:10.2
VIN
2.5V TO 8V 320V
1
2
4
5
346812 TA01
100µF
LT3468 Charging Waveform
3468 G01
1s/DIV
V
IN
= 3.6V
C
OUT
= 100µF
V
OUT
50V/DIV
AVERAGE
INPUT
CURRENT
1A/DIV
TYPICAL APPLICATIO
U
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Protected by U.S. Patents, including 6518733.
LT3468/LT3468-1/LT3468-2
2
346812fa
V
IN
Voltage .............................................................. 16V
SW Voltage ................................................ –0.4V to 50V
CHARGE Voltage...................................................... 10V
DONE Voltage .......................................................... 10V
Current into DONE Pin .......................................... ±1mA
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range (Note 2) ...–40°C to 85°C
Storage Temperature Range ..................–65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
S5 PART
MARKING
T
JMAX
= 125°C
θ
JA
= 150°C ON BOARD OVER
GROUND PLANE
θ
JC
= 90°C/W LTAEC
LTAGQ
LTBCH
LT3468ES5
LT3468ES5-1
LT3468ES5-2
ABSOLUTE AXI U RATI GS
W
WW
U
PACKAGE/ORDER I FOR ATIO
UUW
(Note 1)
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, VCHARGE = VIN unless otherwise noted. (Note 2) Specifications
are for the LT3468, LT3468-1 and LT3468-2 unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Quiescent Current Not Switching 5 8 mA
V
CHARGE
= 0V 0 1 µA
Input Voltage Range ●2.5 16 V
Switch Current Limit LT3468 (Note 3) 1.1 1.2 1.3 A
LT3468-2 0.77 0.87 0.97 A
LT3468-1 0.45 0.55 0.65 A
Switch V
CESAT
LT3468, I
SW
= 1A 330 430 mV
LT3468-2, I
SW
= 650mA 210 280 mV
LT3468-1, I
SW
= 400mA 150 200 mV
V
OUT
Comparator Trip Voltage Measured as V
SW
– V
IN
●31 31.5 32 V
V
OUT
Comparator Overdrive 300ns Pulse Width 200 400 mV
DCM Comparator Trip Voltage Measured as V
SW
– V
IN
●10 36 80 mV
CHARGE Pin Current V
CHARGE
= 3V 15 40 µA
V
CHARGE
= 0V 0 0.1 µA
Switch Leakage Current V
IN
= V
SW
= 5V, in Shutdown ●0.01 1 µA
CHARGE Input Voltage High ●1V
CHARGE Input Voltage Low ●0.3 V
Minimum Charge Pin Low Time High→Low→High 20 µs
DONE Output Signal High 100kΩ from V
IN
to DONE 3 V
DONE Output Signal Low 33µA into DONE Pin 100 200 mV
DONE Leakage Current V
DONE
= 3V, DONE NPN Off 20 100 nA
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT3468E/LT3468E-1/LT3468E-2 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.
Note 3: Specifications are for static test. Current limit in actual application
will be slightly higher.
5 VIN
4 CHARGE
SW 1
TOP VIEW
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
GND 2
DONE 3
LT3468/LT3468-1/LT3468-2
3
346812fa
LT3468-1 Charge Time
LT3468-1 Charging Waveform
LT3468 Input Current LT3468-1 Input Current
LT3468 Charging Waveform
LT3468 Charge Time
VIN (V)
23456789
CHARGE TIME (s)
3468 G04
10
9
8
7
6
5
4
3
2
1
0
COUT = 50µF
COUT = 100µF
TA = 25°C
VIN (V)
23456789
CHARGE TIME (s)
3468 G05
10
9
8
7
6
5
4
3
2
1
0
COUT = 20µF
COUT = 50µF
TA = 25°C
V
OUT
(V)
0 50 100 150 200 250 300
AVERAGE INPUT CURRENT (mA)
3468 G07
800
0
200
400
600
V
IN
= 2.8V
V
IN
= 4.2V
V
IN
= 3.6V
T
A
= 25°C
V
OUT
(V)
0 50 100 150 200 250 300
AVERAGE INPUT CURRENT (mA)
3468 G08
400
0
100
200
300
V
IN
= 2.8V
V
IN
= 4.2V
V
IN
= 3.6V
T
A
= 25°C
V
IN
= 3.6V
C
OUT
= 50µF
3468 G01 3468 G02
TYPICAL PERFOR A CE CHARACTERISTICS
UW
1s/DIV
V
IN
= 3.6V
C
OUT
= 100µF
V
OUT
50V/DIV
1s/DIV
AVERAGE
INPUT
CURRENT
1A/DIV
V
OUT
50V/DIV
AVERAGE
INPUT
CURRENT
0.5A/DIV
LT3468 curves use the circuit of Figure 6, LT3468-1
curves use the circuit of Figure 7 and LT3468-2 use the circuit of Figure 8 unless otherwise noted.
VIN = 3.6V
COUT = 100µF
VOUT
50V/DIV
AVERAGE
INPUT
CURRENT
0.5A/DIV 1s/DIV
3468 G03
V
IN
(V)
2
CHARGE TIME (s)
10
9
8
7
6
5
4
3
2
1
0467
3468 G06
3589
C
OUT
= 100µF
C
OUT
= 50µF
T
A
= 25°C
V
OUT
(V)
0 50 100 150 200 250 300
AVERAGE INPUT CURRENT (mA)
3468 G09
600
0
150
300
450
V
IN
= 2.8V
V
IN
= 4.2V
V
IN
= 3.6V
T
A
= 25°C
LT3468-2 Charge Time
LT3468-2 Charging Waveform
LT3468-2 Input Current
LT3468/LT3468-1/LT3468-2
4
346812fa
LT3468-1 Switch Current Limit
LT3468-1 Output VoltageLT3468 Output Voltage
LT3468 Switch Current Limit
VIN (V)
2345678
VOUT (V)
3468 G13
324
323
322
318
319
320
321
TA = –40°C
TA = 25°C
TA = 85°C
V
IN
(V)
2345678
V
OUT
(V)
3468 G14
324
323
322
318
319
320
321
T
A
= –40°C
T
A
= 25°C
T
A
= 85°C
TEMPERATURE (°C)
–40 –20 0 20 40 60 10080
I
LIM
(A)
3468 G16
1.5
1.1
1.2
1.3
1.4
V
IN
= 3V
V
OUT
= 0V
TEMPERATURE (°C)
–40 –20 0 20 40 60 10080
I
LIM
(A)
3468 G17
0.700
0.500
0.540
0.580
0.620
0.660
V
IN
= 3V
V
OUT
= 0V
TYPICAL PERFOR A CE CHARACTERISTICS
UW
LT3468 curves use the circuit of Figure 6, LT3468-1
curves use the circuit of Figure 7 and LT3468-2 use the circuit of Figure 8 unless otherwise noted.
LT3468 Efficiency LT3468-1 Efficiency
V
OUT
(V)
50 100 150 200 250 300
EFFICIENCY (%)
3468 G10
90
80
40
50
60
70
V
IN
= 2.8V
V
IN
= 4.2V
T
A
= 25°C
V
IN
= 3.6V
V
OUT
(V)
50 100 150 200 250 300
EFFICIENCY (%)
3468 G11
90
80
40
50
60
70
V
IN
= 2.8V
V
IN
= 4.2V
V
IN
= 3.6V
T
A
= 25°C
TEMPERATURE (°C)
–40
ILIM (A)
1.00
0.96
0.92
0.88
0.84
0.80
040 60
34682 G18
–20 20 80 100
VIN = 3V
VOUT = 0V
V
OUT
(V)
50
EFFICIENCY (%)
90
80
70
60
50
40 250
3468 G12
100 150 200 300
T
A
= 25°C
V
IN
= 4.2V
V
IN
= 2.8V
V
IN
= 3.6V
V
IN
(V)
V
OUT
(V)
319
318
317
316
315
314
313
312
3468 G15
2345678
T
A
= 25°C
T
A
= 85°C
T
A
= –40°C
LT3468-2 Switch Current Limit
LT3468-2 Output Voltage
LT3468-2 Efficiency
LT3468/LT3468-1/LT3468-2
5
346812fa
LT3468 Switching Waveform
LT3468/LT3468-1/LT3468-2
Switch Breakdown Voltage
LT3468-1 Switching Waveform
V
IN
= 3.6V
V
OUT
= 100V
3468 G19
1µs/DIV
V
SW
10V/DIV
I
PRI
1A/DIV
V
IN
= 3.6V
V
OUT
= 300V
3468 G23
1µs/DIV
V
SW
10V/DIV
I
PRI
1A/DIV
LT3468 curves use the circuit of Figure 6, LT3468-1
curves use the circuit of Figure 7 and LT3468-2 use the circuit of Figure 8 unless otherwise noted.
TYPICAL PERFOR A CE CHARACTERISTICS
UW
V
SW
10V/DIV
I
PRI
1A/DIV
1µs/DIV
3468 G21
V
IN
= 3.6V
V
OUT
= 100V
VSW
10V/DIV
IPRI
1A/DIV
1µs/DIV 3468 G24
VIN = 3.6V
VOUT = 300V
SWITCH VOLTAGE (V)
0 102030405060708090100
SWITCH CURRENT (mA)
3468 G25
10
9
8
7
6
5
4
3
2
1
0
T = –40°C
T = 25°C
T = 85°C
SW PIN IS RESISTIVE UNTIL BREAKDOWN
VOLTAGE DUE TO INTEGRATED
RESISTORS. THIS DOES NOT INCREASE
QUIESCENT CURRENT OF PART
V
IN
= V
CHARGE
= 5V
LT3468 Switching Waveform
3468 G20
1µs/DIV
V
SW
10V/DIV
I
PRI
1A/DIV
V
IN
= 3.6V
V
OUT
= 300V
LT3468-1 Switching Waveform
V
IN
= 3.6V
V
OUT
= 100V
3468 G22
1µs/DIV
V
SW
10V/DIV
I
PRI
1A/DIV
LT3468-2 Switching Waveform
LT3468-2 Switching Waveform
LT3468/LT3468-1/LT3468-2
6
346812fa
SW (Pin 1): Switch Pin. This is the collector of the internal
NPN Power switch. Minimize the metal trace area con-
nected to this pin to minimize EMI. Tie one side of the
primary of the transformer to this pin. The target output
voltage is set by the turns ratio of the transformer.
Choose Turns Ratio N by the following equation:
NVOUT
=+2
31 5.
Where: V
OUT
is the desired output voltage.
You must tie a Schottky diode from GND to SW, with the
anode at GND for proper operation of the circuit.
Please
refer to the applications section for further information.
GND (Pin 2): Ground. Tie directly to local ground plane.
DONE (Pin 3): Open NPN Collector Indication Pin. When
target output voltage is reached, NPN turns on. This pin
needs a pull-up resistor or current source.
CHARGE (Pin 4): Charge Pin. This pin must be brought
high (>1V) to enable the part. A low (<0.3V) to high (>1V)
transition on this pin puts the part into power delivery
mode. Once the target output voltage is reached, the part
will stop charging the output. Toggle this pin to start
charging again. Ground to shut down. You may bring this
pin low during a charge cycle to halt charging at any time.
V
IN
(Pin 5): Input Supply Pin. Must be locally bypassed
with a good quality ceramic capacitor. Input supply must
be 2.5V or higher.
UU
U
PI FU CTIO S
BLOCK DIAGRA
W
VIN SW
+
DONE
CHARGE
C1
T1
R2
60k
Q1
ENABLE
COUT
PHOTOFLASH
CAPACITOR
36mV
20mV
TO BATTERY
D2
Q2
VOUT
D1
LT3468: RSENSE = 0.015Ω
LT3468-2: RSENSE = 0.022Ω
LT3468-1: RSENSE = 0.03Ω
3486 BD
1
GND
53
4 2
+
–
–
+
–
+
–
+
+–
ONE-
SHOT
ONE-
SHOT
DRIVER
PRIMARY SECONDARY
MASTER
LATCH
RSENSE
DCM COMPARATOR
VOUT COMPARATOR
R1
2.5k S
RQ
1.25V
REFERENCE
Q3
Q1
QQ
SR
A3
A1
A2
CHIP ENABLE
Figure 1
LT3468/LT3468-1/LT3468-2
7
346812fa
indicating that the part has finished charging. Power
delivery can only be restarted by toggling the CHARGE pin.
The CHARGE pin gives full control of the part to the user.
The charging can be halted at any time by bringing the
CHARGE pin low. Only when the final output voltage is
reached will the DONE pin go low. Figure 2 shows these
various modes in action. When CHARGE is first brought
high, charging commences. When CHARGE is brought
low during charging, the part goes into shutdown and
V
OUT
no longer rises. When CHARGE is brought high
again, charging resumes. When the target V
OUT
voltage is
reached, the DONE pin goes low and charging stops.
Finally the CHARGE pin is brought low again so the part
enters shutdown and the DONE pin goes high.
OPERATIO
U
The LT3468/LT3468-1/LT3468-2 are designed to charge
photoflash capacitors quickly and efficiently. The opera-
tion of the part can be best understood by referring to
Figure 1. When the CHARGE pin is first driven high, a one
shot sets both SR latches in the correct state. The power
NPN device, Q1, turns on and current begins ramping up
in the primary of transformer T1. Comparator A1 monitors
the switch current and when the peak current reaches 1.4A
(LT3468), 1A(LT3468-2) or 0.7A (LT3468-1), Q1 is turned
off. Since T1 is utilized as a flyback transformer, the
flyback pulse on the SW pin will cause the output of A3 to
be high. The voltage on the SW pin needs to be at least
36mV higher than V
IN
for this to happen.
During this phase, current is delivered to the photoflash
capacitor via the secondary and diode D1. As the second-
ary current decreases to zero, the SW pin voltage will begin
to collapse. When the SW pin voltage drops to 36mV
above V
IN
or lower, the output of A3 (DCM Comparator)
will go low. This fires a one shot which turns Q1 back on.
This cycle will continue to deliver power to the output.
Output voltage detection is accomplished via R2, R1, Q2,
and comparator A2 (V
OUT
Comparator). Resistors R1 and
R2 are sized so that when the SW voltage is 31.5V above
V
IN
, the output of A2 goes high which resets the master
latch. This disables Q1 and halts power delivery. NPN
transistor Q3 is turned on pulling the DONE pin low,
LT3468-2
V
IN
= 3.6V
C
OUT
= 50µF
V
OUT
100V/DIV
V
CHARGE
5V/DIV
V
DONE
5V/DIV
1s/DIV
3468 F02
Figure 2. Halting the Charging Cycle with the CHARGE Pin
APPLICATIO S I FOR ATIO
WUUU
Choosing The Right Device (LT3468/LT3468-1/
LT3468-2)
The only difference between the three versions of the
LT3468 is the peak current level. For the fastest possible
charge time, use the LT3468. The LT3468-1 has the lowest
peak current capability, and is designed for applications
that need a more limited drain on the batteries. Due to the
lower peak current, the LT3468-1 can use a physically
smaller transformer. The LT3468-2 has a current limit in
between that of the LT3468 and the LT3468-1.
Transformer Design
The flyback transformer is a key element for any LT3468/
LT3468-1/LT3468-2 design. It must be designed carefully
and checked that it does not cause excessive current or
voltage on any pin of the part. The main parameters that
need to be designed are shown in Table 1.
The first transformer parameter that needs to be set is the
turns ratio N. The LT3468/LT3468-1/LT3468-2 accom-
plish output voltage detection by monitoring the flyback
waveform on the SW pin. When the SW voltage reaches
31.5V higher than the V
IN
voltage, the part will halt power
delivery. Thus, the choice of N sets the target output
voltage as it changes the amplitude of the reflected voltage
from the output to the SW pin. Choose N according to the
following equation:
NVOUT
=+2
31 5.
LT3468/LT3468-1/LT3468-2
8
346812fa
Where: V
OUT
is the desired output voltage. The number
2 in the numerator is used to include the effect of the
voltage drop across the output diode(s).
Thus for a 320V output, N should be 322/31.5 or 10.2.
For a 300V output, choose N equal to 302/31.5 or 9.6.
The next parameter that needs to be set is the primary
inductance, L
PRI
. Choose L
PRI
according to the following
formula:
LV
NI
PRI OUT
PK
≥
−
••
•
200 10 9
Where: V
OUT
is the desired output voltage. N is
the transformer turns ratio. I
PK
is 1.4 (LT3468), 0.7
(LT3468-1), and 1.0 (LT3468-2).
L
PRI
needs to be equal or larger than this value to ensure
that the LT3468/LT3468-1/LT3468-2 has adequate time
to respond to the flyback waveform.
All other parameters need to meet or exceed the recom-
mended limits as shown in Table 1. A particularly impor-
tant parameter is the leakage inductance, L
LEAK
. When the
power switch of the LT3468/LT3468-1/LT3468-2 turns
off, the leakage inductance on the primary of the trans-
former causes a voltage spike to occur on the SW pin. The
height of this spike must not exceed 40V, even though the
absolute maximum rating of the SW Pin is 50V. The 50V
absolute maximum rating is a DC blocking voltage speci-
fication, which assumes that the current in the power NPN
is zero. Figure 3 shows the SW voltage waveform for the
circuit of Figure 6(LT3468). Note that the absolute maxi-
mum rating of the SW pin is not exceeded. Make sure to
check the SW voltage waveform with V
OUT
near the target
output voltage, as this is the worst case condition for SW
voltage. Figure 4 shows the various limits on the SW
voltage during switch turn off.
It is important not to minimize the leakage inductance to
a very low level. Although this would result in a very low
leakage spike on the SW pin, the parasitic capacitance of
the transformer would become large. This will adversely
effect the charge time of the photoflash circuit.
Linear Technology has worked with several leading mag-
netic component manufacturers to produce pre-designed
flyback transformers for use with the LT3468/LT3468-1/
LT3468-2. Table 2 shows the details of several of these
transformers.
APPLICATIO S I FOR ATIO
WUUU
Figure 4. New Transformer Design Check (Not to Scale).
Figure 3. LT3468 SW Voltage Waveform
V
IN
= 5V
V
OUT
= 320V
3468 G18
100ns/DIV
V
SW
10V/DIV
Table 1. Recommended Transformer Parameters
TYPICAL RANGE TYPICAL RANGE TYPICAL RANGE
PARAMETER NAME LT3468 LT3468-1 LT3468-2 UNITS
L
PRI
Primary Inductance >5 >10 >7 µH
L
LEAK
Primary Leakage Inductance 100 to 300 200 to 500 200 to 500 nH
N Secondary: Primary Turns Ratio 8 to 12 8 to 12 8 to 12
V
ISO
Secondary to Primary Isolation Voltage >500 >500 >500 V
I
SAT
Primary Saturation Current >1.6 >0.8 >1.0 A
R
PRI
Primary Winding Resistance <300 <500 <400 mΩ
R
SEC
Secondary Winding Resistance <40 <80 <60 Ω
V
SW
3420 F07
0V
“A”
“B”
MUST BE
LESS THAN 40V
MUST BE
LESS THAN 50V
LT3468/LT3468-1/LT3468-2
9
346812fa
Table 2. Pre-Designed Transformers - Typical Specifications Unless Otherwise Noted.
SIZE L
PRI LPRI-LEAKAGE
R
PRI
R
SEC
FOR USE WITH TRANSFORMER NAME (W × L × H) mm (µH) (nH) N (mΩ)(Ω) VENDOR
LT3468/LT3468-2 SBL-5.6-1 5.6 × 8.5 × 4.0 10 200 Max 10.2 103 26 Kijima Musen
LT3468-1 SBL-5.6S-1 5.6 × 8.5 × 3.0 24 400 Max 10.2 305 55 Hong Kong Office
852-2489-8266 (ph)
kijimahk@netvigator.com (email)
LT3468 LDT565630T-001 5.8 × 5.8 × 3.0 6 200 Max 10.4 100 Max 10 Max TDK
LT3468-1 LDT565630T-002 5.8 × 5.8 × 3.0 14.5 500 Max 10.2 240 Max 16.5 Max Chicago Sales Office
LT3468-2 LDT565630T-003 5.8 × 5.8 × 3.0 10.5 550 Max 10.2 210 Max 14 Max (847) 803-6100 (ph)
www.components.tdk.com
LT3468/LT3468-1 T-15-089 6.4 × 7.7 × 4.0 12 400 Max 10.2 211 Max 27 Max Tokyo Coil Engineering
LT3468-1 T-15-083 8.0 × 8.9 × 2.0 20 500 Max 10.2 675 Max 35 Max Japan Office
0426-56-6262 (ph)
www.tokyo-coil.co.jp
Capacitor Selection
For the input bypass capacitor, a high quality X5R or X7R
type should be used. Make sure the voltage capability of
the part is adequate.
Output Diode Selection
The rectifying diode(s) should be low capacitance type
with sufficient reverse voltage and forward current rat-
ings. The peak reverse voltage that the diode(s) will see is
approximately:
VVNV
PK R OUT IN−
=+
()
•
The peak current of the diode is simply:
IN
PK SEC−=14.
(LT3468)
IN
PK SEC−=10.
(LT3468-2)
IN
PK SEC−=07.
(LT3468-1)
For the circuit of Figure 6 with V
IN
of 5V, V
PK-R
is 371V and
I
PK-SEC
is 137mA. The GSD2004S dual silicon diode is
recommended for most LT3468/LT3468-1/LT3468-2
applications. Another option is to use the BAV23S dual
silicon diodes. Diodes Incorporated makes a dual diode
named MMBD3004S which also meets all the require-
ments. Table 3 shows the various diodes and relevant
specifications. Use the appropriate number of diodes to
achieve the necessary reverse breakdown voltage.
SW Pin Clamp Diode Selection
The diode D2 in Figure 6 is needed to clamp the SW node.
Due to the new control scheme of the LT3468/LT3468-1/
LT3468-2, the SW node may go below ground during a
switch cycle. The clamp diode prevents the SW node from
going too far below ground. The diode is required for
proper operation of the circuit. The recommended diode
Table 3. Recommended Output Diodes
MAX REVERSE VOLTAGE MAX FORWARD CONTINUOUS CURRENT CAPACITANCE
PART (V) (mA) (pF) VENDOR
GSD2004S 2x300 225 5 Vishay
(Dual Diode) (402) 563-6866
www.vishay.com
BAV23S 2x250 225 5 Philips Semiconductor
(Dual Diode) (800) 234-7381
www.philips.com
MMBD3004S 2x350 225 5 Diodes Incorporated
(805) 446-4800
www.diodes.com
APPLICATIO S I FOR ATIO
WUUU
LT3468/LT3468-1/LT3468-2
10
346812fa
Board Layout
The high voltage operation of the LT3468/LT3468-1/
LT3468-2 demands careful attention to board layout. You
will not get advertised performance with careless layout.
Figure 5 shows the recommended component placement.
Keep the area for the high voltage end of the secondary as
small as possible. Also note the larger than minimum
spacing for all high voltage nodes in order to meet break-
down voltage requirements for the circuit board.
It is
imperative to keep the electrical path formed by C1, the
primary of T1, and the LT3468/LT3468-1/LT3468-2 as
short as possible.
If this path is haphazardly made long, it
will effectively increase the leakage inductance of T1,
which may result in an overvoltage condition on the SW
pin.
APPLICATIO S I FOR ATIO
WUUU
Figure 5. Suggested Layout: Keep Electrical Path Formed by C1,
Transformer Primary and LT3468/LT3468-1/LT3468-2 Short
D2
R1 D1
(DUAL DIODE)
C1
SECONDARY
PRIMARY
C
OUT
PHOTOFLASH
CAPACITOR
T1
V
IN
CHARGE
DONE
+
•
•
4
5
3
2
1
3468 F05
Table 4. Recommended Clamp Diodes
MAX REVERSE VOLTAGE
PART (V) VENDOR
ZHCS400 40 Zetex
(631) 360-2222
www.zetex.com
B0540W 40 Diodes Inc.
(805) 446-4800
www.diodes.com
MA2Z720 40 Panasonic
(408) 487-9510
www.panasonic.co.jp
TYPICAL APPLICATIO S
U
should be a Schottky diode with at least a 500mA peak
forward current capability. The diode forward voltage drop
should be 600mV or less at 500mA of forward current.
Reverse voltage rating should be 40V or higher. Table 4
shows various recommended clamping diodes.
LT3468
CHARGE
GND
VIN SW
+
DONE DONE
CHARGE
C1
4.7µF
R1
100k
T1
1:10.2
VIN
2.5V TO 8V 320V
1
2
4
5
3468 F06
D2
COUT
PHOTOFLASH
CAPACITOR
C1: 4.7µF, X5R OR X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6-1, LPRI = 10µH, N = 10.2
D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES
D2: ZETEX ZHCS400 OR EQUIVALENT
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
D1
LT3468-1
CHARGE
GND
VIN SW
+
DONE DONE
CHARGE
C1
4.7µF
R1
100k
T1
1:10.2
COUT
PHOTOFLASH
CAPACITOR
VIN
2.5V TO 8V
D2
320V
D1
4
3
5
6
C1: 4.7µF, X5R OR X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6S-1, LPRI = 24µH, N = 10.2
D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES
D2: ZETEX ZHCS400 OR EQUIVALENT
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
3468 F07
Figure 6. LT3468 Photoflash Charger Uses
High Efficiency 4mm Tall Transformer
Figure 7. LT3468-1 Photoflash Charger Uses
High Efficiency 3mm Tall Transformer
LT3468/LT3468-1/LT3468-2
11
346812fa
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
U
PACKAGE DESCRIPTIO
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
TYPICAL APPLICATIO S
U
LT3468-2
CHARGE
GND
VIN SW
+
DONE DONE
CHARGE
C1
4.7µF
R1
100k
T1
1:10.2
COUT
PHOTOFLASH
CAPACITOR
VIN
2.5V TO 8V
D2
320V
D1
5
8
4
1
C1: 4.7µF, X5R OR X7R, 10V
T1: TDK LDT565630T-003 LPRI = 10.5µH, N = 10.2
D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES
D2: ZETEX ZHCS400 OR EQUIVALENT
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
3468 F08
Figure 8. LT3468-2 Photoflash Charger Uses High Efficiency 3mm Tall Transformer
1.50 – 1.75
(NOTE 4)
2.80 BSC
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
DATUM ‘A’
0.09 – 0.20
(NOTE 3)
S5 TSOT-23 0302
PIN ONE
2.90 BSC
(NOTE 4)
0.95 BSC
1.90 BSC
0.80 – 0.90
1.00 MAX
0.01 – 0.10
0.20 BSC
0.30 – 0.50 REF
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3.85 MAX
0.62
MAX
0.95
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
LT3468/LT3468-1/LT3468-2
12
346812fa
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2003
LT/TP 0105 1K REV A • PRINTED IN USA
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS
LTC3407 Dual 600mA (I
OUT
), 1.5MHz, Synchronous Step-Down DC/DC 96% Efficiency, V
IN
: 2.5V to 5.5V, V
OUT(MIN)
: 0.6V, I
Q
: 40µA,
Converter I
SD
: <1µA, MS10E
LT3420/LT3420-1 1.4A/1A, Photoflash Capacitor Chargers with Charges 220µF to 320V in 3.7 seconds from 5V,
Automatic Top-Off V
IN
: 2.2V to 16V, I
Q
: 90µA, I
SD
: <1µA, MS10
LTC3425 5A I
SW
, 8MHz, Multi-Phase Synchronous Step-Up DC/DC 95% Efficiency, V
IN
: 0.5V to 4.5V, V
OUT(MIN)
: 5.25V, I
Q
: 12µA,
Converter I
SD
: <1µA, QFN-32
LTC3440/LTC3441 600mA/1A (I
OUT
), Synchronous Buck-Boost DC/DC Converter 95% Efficiency, V
IN
: 2.5V to 5.5V, V
OUT(MIN)
: 2.5V to 5.5V,
I
Q
: 25µA, I
SD
: <1µA, MS-10, DFN-12
TYPICAL APPLICATIO S
U
LT3468 Photoflash Circuit uses Tiny 3mm Tall Transformer
LT3468-1 Photoflash Circuit uses Tiny 3mm Tall Transformer
LT3468
CHARGE
GND
VIN SW
+
DONE DONE
CHARGE
C1
4.7µF
R1
100k
T1
1:10.4
COUT
PHOTOFLASH
CAPACITOR
VIN
2.5V TO 8V
D2
320V
D1
4
3
1
5, 6
7, 8
4
1
5
2
C1: 4.7µF, X5R OR X7R, 10V
T1: TDK PART# LDT565630T-001, LPRI = 6µH, N = 10.4
D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES
D2: ZETEX ZHCS400 OR EQUIVALENT
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
3468 TA03
LT3468-1
CHARGE
GND
V
IN
SW
+
DONE DONE
CHARGE
C1
4.7µF
R1
100k
T1
1:10.2
COUT
PHOTOFLASH
CAPACITOR
VIN
2.5V TO 8V
D2
320V
D1
4
3
1
5
8
4
1
5
2
C1: 4.7µF, X5R OR X7R, 10V
T1: TDK PART# LDT565630T-002, L
PRI
= 14.5µH, N = 10.2
D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES
D2: ZETEX ZHCS400 OR EQUIVALENT
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
3468 TA04
Charge Time
Charge Time
V
IN
(V)
23456789
CHARGE TIME (s)
3468 TA05
10
9
8
7
6
5
4
3
2
1
0
C
OUT
= 50µF
C
OUT
= 100µF
V
IN
(V)
23456789
CHARGE TIME (s)
3468 TA06
10
9
8
7
6
5
4
3
2
1
0
C
OUT
= 20µF
C
OUT
= 50µF
