LT3468_15 [Linear]
Photoflash Capacitor Chargers in ThinSOT;
| 型号： | LT3468_15 |
| 厂家： | 
Linear |
| 描述： | Photoflash Capacitor Chargers in ThinSOT |
| 文件： | 总12页 (文件大小：459K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3468/LT3468-1/LT3468-2
Photoflash Capacitor
Chargers in ThinSOTTM
U
FEATURES
DESCRIPTIO
The LT®3468/LT3468-1/LT3468-2 are highly integrated
ICsdesignedtochargephotoflashcapacitorsindigitaland
filmcameras. Apatentedcontroltechnique*allowsforthe
useofextremelysmalltransformers.Eachdevicecontains
anon-chiphighvoltageNPNpowerswitch.Outputvoltage
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.
■
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, VIN = 3.6V)
5.7s for LT3468-2 (0V to 320V, 100µF, VIN = 3.6V)
5.5s for LT3468-1 (0V to 320V, 50µF, VIN = 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
The CHARGE pin gives full control of the part to the user.
DrivingCHARGElowputsthepartinshutdown. TheDONE
pin indicates when the part has completed charging. The
LT3468 series of parts are available in tiny low profile
(1mm) SOT-23 packages.
, 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.
■
Low Profile (<1mm) SOT-23 Package
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APPLICATIO S
■
Digital / Film Camera Flash
■
PDA / Cell Phone Flash
■
Emergency Strobe
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TYPICAL APPLICATIO
LT3468 Photoflash Charger Uses
High Efficiency 4mm Tall Transformer
LT3468 Charging Waveform
DANGER HIGH VOLTAGE – OPERATION BY HIGH VOLTAGE
TRAINED PERSONNEL ONLY
VIN = 3.6V
COUT = 100µF
1:10.2
V
IN
320V
2.5V TO 8V
1
2
4
5
4.7µF
VOUT
50V/DIV
+
100µF
V
SW
IN
100k
AVERAGE
INPUT
LT3468
CURRENT
DONE
DONE
GND
1A/DIV
1s/DIV
3468 G01
CHARGE
CHARGE
346812 TA01
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LT3468/LT3468-1/LT3468-2
W W U W
ABSOLUTE AXI U RATI GS
(Note 1)
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PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
VIN 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
TOP VIEW
LT3468ES5
LT3468ES5-1
LT3468ES5-2
SW 1
GND 2
5 VIN
DONE 3
4 CHARGE
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
S5 PART
MARKING
TJMAX = 125°C
θJA = 150°C ON BOARD OVER
GROUND PLANE
LTAEC
LTAGQ
LTBCH
θJC = 90°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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
0
8
1
mA
µA
V
= 0V
CHARGE
Input Voltage Range
Switch Current Limit
●
2.5
16
V
LT3468 (Note 3)
LT3468-2
LT3468-1
1.1
0.77
0.45
1.2
0.87
0.55
1.3
0.97
0.65
A
A
A
Switch V
LT3468, I = 1A
330
210
150
430
280
200
mV
mV
mV
CESAT
SW
LT3468-2, I = 650mA
SW
LT3468-1, I = 400mA
SW
V
V
Comparator Trip Voltage
Comparator Overdrive
Measured as V – V
●
●
31
10
31.5
200
36
32
400
80
V
mV
mV
OUT
OUT
SW
IN
300ns Pulse Width
DCM Comparator Trip Voltage
CHARGE Pin Current
Measured as V – V
SW
IN
V
V
= 3V
= 0V
15
0
40
0.1
µA
µA
CHARGE
CHARGE
Switch Leakage Current
V
= V = 5V, in Shutdown
●
●
●
0.01
1
µA
V
IN
SW
CHARGE Input Voltage High
CHARGE Input Voltage Low
Minimum Charge Pin Low Time
DONE Output Signal High
DONE Output Signal Low
DONE Leakage Current
1
0.3
V
High→Low→High
20
3
µs
V
100kΩ from V to DONE
IN
33µA into DONE Pin
100
20
200
100
mV
nA
V
= 3V, DONE NPN Off
DONE
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
–40°C to 85°C operating temperature range are assured by design,
characterization and correlation with statistical process.
Note 2: The LT3468E/LT3468E-1/LT3468E-2 are guaranteed to meet
performance specifications from 0°C to 70°C. Specifications over the
Note 3: Specifications are for static test. Current limit in actual application
will be slightly higher.
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LT3468/LT3468-1/LT3468-2
U W
TYPICAL PERFOR A CE CHARACTERISTICS 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 Charging Waveform
LT3468-1 Charging Waveform
LT3468-2 Charging Waveform
V
C
= 3.6V
IN
OUT
VIN = 3.6V
COUT = 100µF
VIN = 3.6V
COUT = 50µF
= 100µF
V
OUT
50V/DIV
VOUT
50V/DIV
VOUT
50V/DIV
AVERAGE
INPUT
CURRENT
0.5A/DIV
AVERAGE
INPUT
CURRENT
1A/DIV
AVERAGE
INPUT
CURRENT
0.5A/DIV
3468 G03
1s/DIV
1s/DIV
1s/DIV
3468 G01
3468 G02
LT3468-1 Charge Time
LT3468-2 Charge Time
LT3468 Charge Time
10
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
T
= 25°C
T = 25°C
A
T
= 25°C
A
A
C
= 100µF
OUT
C
5
= 50µF
OUT
C
= 100µF
OUT
C
= 50µF
OUT
4
C
= 50µF
OUT
3
C
= 20µF
OUT
3
2
5
6
7
8
9
3
2
4
5
6
7
8
9
2
4
6
7
8
9
V
(V)
IN
V
(V)
IN
V
(V)
IN
3468 G06
3468 G04
3468 G05
LT3468 Input Current
LT3468-1 Input Current
LT3468-2 Input Current
800
600
400
200
0
400
300
200
100
0
600
450
300
150
0
T
= 25°C
T
= 25°C
T = 25°C
A
A
A
V
= 2.8V
IN
V
= 2.8V
IN
V
= 2.8V
IN
V
= 4.2V
IN
V
= 4.2V
IN
V
= 3.6V
V
= 4.2V
IN
IN
V
= 3.6V
IN
V
= 3.6V
IN
0
50
100 150 200 250 300
(V)
0
50
100 150 200 250 300
(V)
0
50
100 150 200 250 300
(V)
V
V
V
OUT
OUT
OUT
3468 G07
3468 G08
3468 G09
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LT3468/LT3468-1/LT3468-2
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TYPICAL PERFOR A CE CHARACTERISTICS 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.
LT3468-2 Efficiency
LT3468 Efficiency
LT3468-1 Efficiency
90
80
70
60
50
40
90
80
70
60
50
40
90
80
70
60
50
40
T
= 25°C
T
= 25°C
T
= 25°C
A
A
A
V
= 4.2V
V
= 4.2V
IN
IN
V
= 4.2V
IN
V
= 2.8V
IN
V
= 2.8V
V
= 2.8V
IN
IN
V
= 3.6V
V
= 3.6V
V
= 3.6V
IN
IN
IN
50
100
150
200
(V)
250
300
50
100
150
200
(V)
250
300
50
100
150
200
(V)
250
300
V
V
OUT
V
OUT
OUT
3468 G10
3468 G11
3468 G12
LT3468-2 Output Voltage
LT3468 Output Voltage
LT3468-1 Output Voltage
324
324
319
318
317
316
315
314
313
312
T
= –40°C
323
322
321
320
319
318
323
322
321
320
319
318
A
T
A
= –40°C
A
T
A
= 25°C
T
= 25°C
T
= 85°C
A
T
= 25°C
A
T
= 85°C
T
A
= 85°C
A
T
= –40°C
A
2
3
4
5
6
7
8
2
3
4
5
6
7
8
2
4
5
6
7
8
3
V
(V)
V
IN
(V)
V
IN
(V)
IN
3468 G13
3468 G14
3468 G15
LT3468-2 Switch Current Limit
LT3468-1 Switch Current Limit
LT3468 Switch Current Limit
1.00
0.96
0.92
0.88
0.84
0.80
1.5
1.4
1.3
1.2
1.1
0.700
0.660
0.620
0.580
0.540
0.500
V
V
= 3V
V
V
= 3V
IN
OUT
IN
OUT
V
V
= 3V
IN
OUT
= 0V
= 0V
= 0V
–40 –20
0
20
40
60
80 100
–40
0
20
40
60
80 100
–20
–40 –20
0
20
40
60
80 100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
3468 G16
34682 G18
3468 G17
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LT3468/LT3468-1/LT3468-2
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TYPICAL PERFOR A CE CHARACTERISTICS 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.
LT3468-2 Switching Waveform
LT3468 Switching Waveform
LT3468-1 Switching Waveform
VIN = 3.6V
VOUT = 100V
V
V
= 3.6V
VIN = 3.6V
IN
OUT
= 100V
V
OUT = 100V
VSW
10V/DIV
VSW
10V/DIV
V
SW
10V/DIV
IPRI
1A/DIV
IPRI
1A/DIV
I
PRI
1A/DIV
3468 G21
1µs/DIV
1µs/DIV
1µs/DIV
3468 G19
3468 G22
LT3468-2 Switching Waveform
LT3468-1 Switching Waveform
LT3468 Switching Waveform
V
V
= 3.6V
VIN = 3.6V
VOUT = 300V
VIN = 3.6V
VOUT = 300V
IN
OUT
= 300V
V
VSW
10V/DIV
SW
VSW
10V/DIV
10V/DIV
IPRI
1A/DIV
I
PRI
IPRI
1A/DIV
1A/DIV
1µs/DIV
3468 G24
1µs/DIV
1µs/DIV
3468 G23
3468 G20
LT3468/LT3468-1/LT3468-2
Switch Breakdown Voltage
10
9
8
7
6
5
4
3
2
1
0
SW PIN IS RESISTIVE UNTIL BREAKDOWN
VOLTAGE DUE TO INTEGRATED
RESISTORS. THIS DOES NOT INCREASE
QUIESCENT CURRENT OF PART
T = 25°C
T = –40°C
T = 85°C
V
IN
= V = 5V
CHARGE
0
10 20 30 40 50 60 70 80 90 100
SWITCH VOLTAGE (V)
3468 G25
346812fa
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LT3468/LT3468-1/LT3468-2
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PI FU CTIO S
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.
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.
Choose Turns Ratio N by the following equation:
V
OUT + 2
31.5
N =
Where: VOUT is the desired output voltage.
VIN (Pin 5): Input Supply Pin. Must be locally bypassed
with a good quality ceramic capacitor. Input supply must
be 2.5V or higher.
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.
W
BLOCK DIAGRA
D1
T1
V
TO BATTERY
OUT
PRIMARY
SECONDARY
C1
D2
DONE
V
SW
1
IN
+
C
OUT
3
5
PHOTOFLASH
CAPACITOR
R2
60k
Q3
DCM COMPARATOR
+
ONE-
SHOT
A3
–
+
36mV
–
Q2
Q1
ENABLE
MASTER
LATCH
R1
2.5k
DRIVER
S
Q
S
Q
R
Q1
R
Q
+
A2
1.25V
REFERENCE
+
–
–
R
A1
SENSE
20mV
V
COMPARATOR
OUT
+–
CHARGE
GND
ONE-
SHOT
4
2
CHIP ENABLE
3486 BD
LT3468: R
= 0.015Ω
SENSE
LT3468-2: R
= 0.022Ω
= 0.03Ω
SENSE
SENSE
LT3468-1: R
Figure 1
346812fa
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LT3468/LT3468-1/LT3468-2
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OPERATIO
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
intheprimaryoftransformerT1. ComparatorA1monitors
theswitchcurrentandwhenthepeakcurrentreaches1.4A
(LT3468),1A(LT3468-2)or0.7A(LT3468-1),Q1isturned
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 VIN for this to happen.
indicating that the part has finished charging. Power
deliverycanonlyberestartedbytogglingtheCHARGEpin.
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
VOUT no longer rises. When CHARGE is brought high
again, charging resumes. When the target VOUT 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.
During this phase, current is delivered to the photoflash
capacitor via the secondary and diode D1. As the second-
arycurrentdecreasestozero,theSWpinvoltagewillbegin
to collapse. When the SW pin voltage drops to 36mV
above VIN 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.
LT3468-2
V
C
= 3.6V
IN
OUT
= 50µF
V
OUT
100V/DIV
V
DONE
5V/DIV
Output voltage detection is accomplished via R2, R1, Q2,
and comparator A2 (VOUT Comparator). Resistors R1 and
R2 are sized so that when the SW voltage is 31.5V above
VIN, 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,
V
CHARGE
5V/DIV
3468 F02
1s/DIV
Figure 2. Halting the Charging Cycle with the CHARGE Pin
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APPLICATIO S I FOR ATIO
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.
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
chargetime,usetheLT3468.TheLT3468-1hasthelowest
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.
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 VIN voltage, the part will halt power
delivery. Thus, the choice of N sets the target output
voltageasitchangestheamplitudeofthereflectedvoltage
from the output to the SW pin. Choose N according to the
following equation:
Transformer Design
The flyback transformer is a key element for any LT3468/
LT3468-1/LT3468-2 design. It must be designed carefully
V
OUT + 2
31.5
N =
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LT3468/LT3468-1/LT3468-2
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APPLICATIO S I FOR ATIO
Where: VOUT 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).
off, the leakage inductance on the primary of the trans-
former causes a voltage spike to occur on the SW pin. The
heightofthisspikemustnotexceed40V,eventhoughthe
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 VOUT 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.
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, LPRI. Choose LPRI according to the following
formula:
VOUT • 200 •10−9
LPRI
≥
N •IPK
Where: VOUT is the desired output voltage. N is
the transformer turns ratio. IPK is 1.4 (LT3468), 0.7
(LT3468-1), and 1.0 (LT3468-2).
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.
LPRI 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.
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.
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, LLEAK. When the
power switch of the LT3468/LT3468-1/LT3468-2 turns
Table 1. Recommended Transformer Parameters
TYPICAL RANGE
LT3468
TYPICAL RANGE
LT3468-1
TYPICAL RANGE
LT3468-2
PARAMETER
NAME
UNITS
µH
L
L
Primary Inductance
>5
100 to 300
8 to 12
>500
>10
200 to 500
8 to 12
>500
>7
200 to 500
8 to 12
>500
PRI
Primary Leakage Inductance
Secondary: Primary Turns Ratio
Secondary to Primary Isolation Voltage
Primary Saturation Current
Primary Winding Resistance
Secondary Winding Resistance
nH
LEAK
N
V
V
A
ISO
I
>1.6
>0.8
>1.0
SAT
R
R
<300
<500
<400
mΩ
Ω
PRI
<40
<80
<60
SEC
VIN = 5V
OUT = 320V
V
“B”
MUST BE
LESS THAN 50V
“A”
MUST BE
LESS THAN 40V
V
SW
0V
VSW
10V/DIV
3420 F07
100ns/DIV
3468 G18
Figure 3. LT3468 SW Voltage Waveform
Figure 4. New Transformer Design Check (Not to Scale).
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LT3468/LT3468-1/LT3468-2
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APPLICATIO S I FOR ATIO
Table 2. Pre-Designed Transformers - Typical Specifications Unless Otherwise Noted.
SIZE
L
R
(mΩ)
R
SEC
(Ω)
PRI
LPRI-LEAKAGE
PRI
FOR USE WITH
TRANSFORMER NAME (W × L × H) mm (µH)
(nH)
N
VENDOR
LT3468/LT3468-2
LT3468-1
SBL-5.6-1
SBL-5.6S-1
5.6 × 8.5 × 4.0
5.6 × 8.5 × 3.0
10
24
200 Max
400 Max
10.2
10.2
103
305
26
55
Kijima Musen
Hong Kong Office
852-2489-8266 (ph)
kijimahk@netvigator.com (email)
LT3468
LT3468-1
LT3468-2
LDT565630T-001
LDT565630T-002
LDT565630T-003
5.8 × 5.8 × 3.0
5.8 × 5.8 × 3.0
5.8 × 5.8 × 3.0
6
14.5
10.5
200 Max
500 Max
550 Max
10.4 100 Max 10 Max
10.2 240 Max 16.5 Max
10.2 210 Max 14 Max
TDK
Chicago Sales Office
(847) 803-6100 (ph)
www.components.tdk.com
LT3468/LT3468-1
LT3468-1
T-15-089
T-15-083
6.4 × 7.7 × 4.0
8.0 × 8.9 × 2.0
12
20
400 Max
500 Max
10.2 211 Max 27 Max
10.2 675 Max 35 Max
Tokyo Coil Engineering
Japan Office
0426-56-6262 (ph)
www.tokyo-coil.co.jp
Capacitor Selection
0.7
N
IPK−SEC
=
(LT3468-1)
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.
For the circuit of Figure 6 with VIN of 5V, VPK-R is 371V and
IPK-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.
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:
V
PK−R = VOUT + N • V
(
)
IN
SW Pin Clamp Diode Selection
The peak current of the diode is simply:
1.4
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
IPK−SEC
=
(LT3468)
N
1.0
N
IPK−SEC
=
(LT3468-2)
Table 3. Recommended Output Diodes
MAX REVERSE VOLTAGE MAX FORWARD CONTINUOUS CURRENT
CAPACITANCE
(pF)
PART
(V)
(mA)
VENDOR
GSD2004S
2x300
225
5
5
5
Vishay
(402) 563-6866
www.vishay.com
(Dual Diode)
BAV23S
(Dual Diode)
2x250
2x350
225
225
Philips Semiconductor
(800) 234-7381
www.philips.com
MMBD3004S
Diodes Incorporated
(805) 446-4800
www.diodes.com
346812fa
9
LT3468/LT3468-1/LT3468-2
U
W
U U
APPLICATIO S I FOR ATIO
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.
should be a Schottky diode with at least a 500mA peak
forwardcurrentcapability.Thediodeforwardvoltagedrop
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.
Table 4. Recommended Clamp Diodes
MAX REVERSE VOLTAGE
PART
(V)
VENDOR
ZHCS400
40
Zetex
(631) 360-2222
www.zetex.com
V
IN
C1
R1
D1
(DUAL DIODE)
DONE
B0540W
40
40
Diodes Inc.
(805) 446-4800
www.diodes.com
CHARGE
+
C
4
5
3
2
1
•
OUT
PHOTOFLASH
CAPACITOR
T1
•
MA2Z720
Panasonic
(408) 487-9510
www.panasonic.co.jp
D2
Board Layout
3468 F05
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.
Figure 5. Suggested Layout: Keep Electrical Path Formed by C1,
Transformer Primary and LT3468/LT3468-1/LT3468-2 Short
U
TYPICAL APPLICATIO S
T1
D1
T1
1:10.2
D1
1:10.2
V
IN
V
320V
OUT
IN
320V
2.5V TO 8V
4
3
5
6
2.5V TO 8V
1
2
4
5
C1
4.7µF
C1
4.7µF
+
C
+
C
OUT
PHOTOFLASH
CAPACITOR
PHOTOFLASH
CAPACITOR
V
SW
LT3468-1
IN
V
SW
R1
D2
IN
R1
100k
D2
100k
LT3468
DONE
DONE
GND
DONE
DONE
GND
CHARGE
CHARGE
CHARGE
CHARGE
3468 F06
C1: 4.7µF, X5R OR X7R, 10V
C1: 4.7µF, X5R OR X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6S-1, L = 24µH, N = 10.2
PRI
T1: KIJIMA MUSEN PART# SBL-5.6-1, L = 10µH, N = 10.2
PRI
D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES
D2: ZETEX ZHCS400 OR EQUIVALENT
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
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
346812fa
10
LT3468/LT3468-1/LT3468-2
U
TYPICAL APPLICATIO S
T1
1:10.2
D1
V
IN
320V
2.5V TO 8V
5
8
4
1
C1
4.7µF
+
C
OUT
PHOTOFLASH
CAPACITOR
V
SW
LT3468-2
IN
R1
100k
D2
DONE
DONE
GND
CHARGE
CHARGE
C1: 4.7µF, X5R OR X7R, 10V
T1: TDK LDT565630T-003 L = 10.5µH, N = 10.2
PRI
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
U
PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
0.62
MAX
0.95
REF
2.90 BSC
(NOTE 4)
1.22 REF
1.50 – 1.75
(NOTE 4)
2.80 BSC
1.4 MIN
3.85 MAX 2.62 REF
PIN ONE
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
DATUM ‘A’
0.01 – 0.10
1.00 MAX
0.30 – 0.50 REF
1.90 BSC
0.09 – 0.20
(NOTE 3)
NOTE:
S5 TSOT-23 0302
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
346812fa
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-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
11
LT3468/LT3468-1/LT3468-2
U
TYPICAL APPLICATIO S
LT3468 Photoflash Circuit uses Tiny 3mm Tall Transformer
Charge Time
T1
D1
1:10.4
V
10
9
8
7
6
5
4
3
2
1
0
IN
320V
2.5V TO 8V
5, 6
7, 8
4
1
C1
4.7µF
+
C
OUT
PHOTOFLASH
CAPACITOR
5
1
V
SW
IN
R1
100k
D2
LT3468
2
3
4
DONE
DONE
GND
C
= 100µF
OUT
CHARGE
CHARGE
C
= 50µF
OUT
3
C1: 4.7µF, X5R OR X7R, 10V
T1: TDK PART# LDT565630T-001, L = 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
PRI
2
4
5
6
7
8
9
3468 TA03
V
(V)
IN
3468 TA05
LT3468-1 Photoflash Circuit uses Tiny 3mm Tall Transformer
T1
D1
Charge Time
1:10.2
V
IN
10
9
8
7
6
5
4
3
2
1
0
320V
2.5V TO 8V
5
8
4
1
C1
4.7µF
+
C
OUT
PHOTOFLASH
CAPACITOR
5
1
V
SW
IN
R1
100k
D2
LT3468-1
2
3
4
DONE
DONE
GND
C
= 50µF
OUT
CHARGE
CHARGE
C1: 4.7µF, X5R OR X7R, 10V
C
= 20µF
OUT
T1: TDK PART# LDT565630T-002, L = 14.5µH, N = 10.2
PRI
D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES
D2: ZETEX ZHCS400 OR EQUIVALENT
2
3
4
5
6
7
8
9
3468 TA04
V
(V)
IN
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED
3468 TA06
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC3407
Dual 600mA (I ), 1.5MHz, Synchronous Step-Down DC/DC 96% Efficiency, V : 2.5V to 5.5V, V
: 0.6V, I : 40µA,
OUT(MIN) Q
OUT
IN
Converter
I : <1µA, MS10E
SD
LT3420/LT3420-1
LTC3425
1.4A/1A, Photoflash Capacitor Chargers with
Automatic Top-Off
Charges 220µF to 320V in 3.7 seconds from 5V,
V : 2.2V to 16V, I : 90µA, I : <1µA, MS10
IN
Q
SD
5A I , 8MHz, Multi-Phase Synchronous Step-Up DC/DC
95% Efficiency, V : 0.5V to 4.5V, V
: 5.25V, I : 12µA,
OUT(MIN)
SW
IN
Q
Converter
I : <1µA, QFN-32
SD
LTC3440/LTC3441
600mA/1A (I ), Synchronous Buck-Boost DC/DC Converter 95% Efficiency, V : 2.5V to 5.5V, V
: 2.5V to 5.5V,
OUT(MIN)
OUT
IN
I : 25µA, I : <1µA, MS-10, DFN-12
Q
SD
346812fa
LT/TP 0105 1K REV A • PRINTED IN USA
12 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
©LINEAR TECHNOLOGY CORPORATION 2003
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