LINEAR TECHNOLOGY LT3468, LT3468-1, LT3468-2 Technical data

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FEATURES

LT3468/LT3468-1/LT3468-2

Photoflash Capacitor

Chargers in ThinSOT

DESCRIPTIO

■

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

5.7s for LT3468-2 (0V to 320V, 100µF, V

= 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

■

Low Profile (<1mm) SOT-23 Package

APPLICATIO S

■

Digital / Film Camera Flash

■

PDA / Cell Phone Flash

■

Emergency Strobe

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.

, 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.

TYPICAL APPLICATIO

LT3468 Photoflash Charger Uses

High Efficiency 4mm Tall Transformer

DANGER HIGH VOLTAGE – OPERATION BY HIGH VOLTAGE

TRAINED PERSONNEL ONLY

2.5V TO 8V

100k

DONE DONE

CHARGE

4.7µF

CHARGE

LT3468

1:10.2

GND

LT3468 Charging Waveform

VIN = 3.6V

= 100µF

OUT

320V

100µF

346812 TA01

OUT

50V/DIV

AVERAGE

INPUT

CURRENT

1A/DIV

1s/DIV

3468 G01

346812fa

LT3468/LT3468-1/LT3468-2

5 VIN

4 CHARGE

SW 1

TOP VIEW

S5 PACKAGE

5-LEAD PLASTIC TSOT-23

GND 2

DONE 3

ABSOLUTE AXI U RATI GS

(Note 1)

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

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at TA = 25°C. VIN = 3V, V 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

Input Voltage Range ● 2.5 16 V

Switch Current Limit LT3468 (Note 3) 1.1 1.2 1.3 A

Switch V

OUT

DCM Comparator Trip Voltage Measured as V

CHARGE Pin Current V

Switch Leakage Current VIN = VSW = 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 VIN to DONE 3 V

DONE Output Signal Low 33µA into DONE Pin 100 200 mV

DONE Leakage Current V

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

UUW

PACKAGE/ORDER I FOR ATIO

ORDER PART

NUMBER

LT3468ES5 LT3468ES5-1 LT3468ES5-2

S5 PART

= 125°C

JMAX

= 150°C ON BOARD OVER

GROUND PLANE

θJC = 90°C/W

Consult LTC Marketing for parts specified with wider operating temperature ranges.

The ● denotes the specifications which apply over the full operating

= VIN unless otherwise noted. (Note 2) Specifications

CHARGE

= 0V 0 1 µA

CHARGE

LT3468-2 0.77 0.87 0.97 A LT3468-1 0.45 0.55 0.65 A

CESAT

Comparator Trip Voltage Measured as V

Comparator Overdrive 300ns Pulse Width 200 400 mV

LT3468, I LT3468-2, I LT3468-1, I

CHARGE

DONE

= 1A 330 430 mV

= 650mA 210 280 mV

= 400mA 150 200 mV

– V

= 3V 15 40 µA = 0V 0 0.1 µA

= 3V, DONE NPN Off 20 100 nA

–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.

● 31 31.5 32 V

● 10 36 80 mV

MARKING

LTAEC LTAGQ LTBCH

346812fa

LT3468/LT3468-1/LT3468-2

TYPICAL PERFOR A CE CHARACTERISTICS

curves use the circuit of Figure 7 and LT3468-2 use the circuit of Figure 8 unless otherwise noted.

LT3468 curves use the circuit of Figure 6, LT3468-1

LT3468 Charging Waveform

VIN = 3.6V

= 100µF

OUT

50V/DIV

AVERAGE

INPUT

CURRENT

1A/DIV

1s/DIV

LT3468 Charge Time

TA = 25°C

CHARGE TIME (s)

OUT

23456789

= 50µF

OUT

= 100µF

VIN (V)

3468 G01

3468 G04

LT3468-1 Charging Waveform

VIN = 3.6V

= 50µF

OUT

50V/DIV

AVERAGE

INPUT

CURRENT

0.5A/DIV

1s/DIV

LT3468-1 Charge Time

TA = 25°C

CHARGE TIME (s)

OUT

23456789

= 20µF

OUT

VIN (V)

= 50µF

3468 G02

3468 G05

OUT

50V/DIV

AVERAGE

INPUT

CURRENT

0.5A/DIV

CHARGE TIME (s)

LT3468-2 Charging Waveform

VIN = 3.6V C

= 100µF

OUT

1s/DIV

LT3468-2 Charge Time

TA = 25°C

= 100µF

OUT

= 50µF

OUT

VIN (V)

3468 G03

3468 G06

LT3468 Input Current LT3468-1 Input Current

800

TA = 25°C

600

400

200

AVERAGE INPUT CURRENT (mA)

VIN = 2.8V

VIN = 4.2V

VIN = 3.6V

0 50 100 150 200 250 300

(V)

OUT

3468 G07

400

TA = 25°C

300

VIN = 2.8V

200

100

AVERAGE INPUT CURRENT (mA)

0 50 100 150 200 250 300

VIN = 4.2V

VIN = 3.6V

LT3468-2 Input Current

600

TA = 25°C

450

VIN = 2.8V

300

150

AVERAGE INPUT CURRENT (mA)

(V)

OUT

3468 G08

0 50 100 150 200 250 300

VIN = 3.6V

OUT

VIN = 4.2V

(V)

3468 G09

346812fa

LT3468/LT3468-1/LT3468-2

TEMPERATURE (°C)

–40

LIM

(A)

1.00

0.96

0.92

0.88

0.84

0.80 0

34682 G18

–20

100

VIN = 3V V

OUT

= 0V

TYPICAL PERFOR A CE CHARACTERISTICS

curves use the circuit of Figure 7 and LT3468-2 use the circuit of Figure 8 unless otherwise noted.

LT3468 curves use the circuit of Figure 6, LT3468-1

LT3468 Efficiency LT3468-1 Efficiency

TA = 25°C

VIN = 2.8V

EFFICIENCY (%)

50 100 150 200 250 300

VIN = 4.2V

VIN = 3.6V

(V)

OUT

3468 G10

TA = 25°C

VIN = 2.8V

EFFICIENCY (%)

50 100 150 200 250 300

LT3468-1 Output VoltageLT3468 Output Voltage

(V)

OUT

324

323

322

321

320

319

TA = –40°C

TA = 25°C

TA = 85°C

(V)

OUT

324

323

322

321

320

319

TA = –40°C

TA = 25°C

TA = 85°C

VIN = 4.2V

VIN = 3.6V

OUT

(V)

3468 G11

LT3468-2 Efficiency

TA = 25°C

VIN = 2.8V

EFFICIENCY (%)

100

VIN = 3.6V

150

LT3468-2 Output Voltage

319

318

317

(V)

OUT

316

315

314

313

TA = 85°C

TA = –40°C

OUT

200

(V)

VIN = 4.2V

250

TA = 25°C

300

3468 G12

318

2345678

VIN (V)

LT3468 Switch Current Limit

1.5 VIN = 3V

= 0V

OUT

1.4

(A)

1.3

LIM

1.2

1.1

–40 –20 0 20 40 60 10080

TEMPERATURE (°C)

3468 G13

3468 G16

318

2345678

VIN (V)

LT3468-1 Switch Current Limit

0.700 VIN = 3V

= 0V

OUT

0.660

0.620

(A)

LIM

0.580

0.540

0.500

–40 –20 0 20 40 60 10080

TEMPERATURE (°C)

3468 G14

3468 G17

312

45678

VIN (V)

LT3468-2 Switch Current Limit

3468 G15

346812fa

LT3468/LT3468-1/LT3468-2

TYPICAL PERFOR A CE CHARACTERISTICS

curves use the circuit of Figure 7 and LT3468-2 use the circuit of Figure 8 unless otherwise noted.

LT3468 curves use the circuit of Figure 6, LT3468-1

LT3468 Switching Waveform

VIN = 3.6V

= 100V

OUT

10V/DIV

PRI

1A/DIV

1µs/DIV

LT3468 Switching Waveform

VIN = 3.6V

= 300V

OUT

10V/DIV

PRI

1A/DIV

3468 G19

LT3468-1 Switching Waveform

VIN = 3.6V V

= 100V

OUT

10V/DIV

PRI

1A/DIV

1µs/DIV

LT3468-1 Switching Waveform

VIN = 3.6V

= 300V

OUT

10V/DIV

PRI

1A/DIV

3468 G22

LT3468-2 Switching Waveform

VIN = 3.6V

= 100V

OUT

10V/DIV

PRI

1A/DIV

1µs/DIV

LT3468-2 Switching Waveform

VIN = 3.6V

= 300V

OUT

10V/DIV

PRI

1A/DIV

3468 G21

1µs/DIV

3468 G20

1µs/DIV

LT3468/LT3468-1/LT3468-2 Switch Breakdown Voltage

SW PIN IS RESISTIVE UNTIL BREAKDOWN VOLTAGE DUE TO INTEGRATED

RESISTORS. THIS DOES NOT INCREASE

QUIESCENT CURRENT OF PART

SWITCH CURRENT (mA)

0 102030405060708090100

SWITCH VOLTAGE (V)

T = 25°C

T = –40°C

VIN = V

T = 85°C

CHARGE

3468 G23

= 5V

3468 G25

1µs/DIV

3468 G24

346812fa

LT3468/LT3468-1/LT3468-2

PI FU CTIO S

SW (Pin 1): Switch Pin. This is the collector of the internal NPN Power switch. Minimize the metal trace area connected 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:

+ 2

OUT

31 5.

Where: V

is the desired output voltage.

OUT

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.

BLOCK DIAGRA

TO BATTERY

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.

(Pin 5): Input Supply Pin. Must be locally bypassed

with a good quality ceramic capacitor. Input supply must be 2.5V or higher.

PRIMARY SECONDARY

OUT

DONE

60k

DCM COMPARATOR

ONE-

SHOT

MASTER

LATCH

ENABLE

QQ SR

–

COMPARATOR

OUT

CHARGE

ONE-

4 2

SHOT

CHIP ENABLE

LT3468: R LT3468-2: R LT3468-1: R

SENSE

SENSE SENSE

= 0.015Ω

= 0.022Ω = 0.03Ω

2.5k

1.25V

REFERENCE

Figure 1

–

+ –

DRIVER

20mV

–

+–

36mV

SENSE

GND

3486 BD

OUT

PHOTOFLASH CAPACITOR

346812fa

OPERATIO

LT3468/LT3468-1/LT3468-2

The LT3468/LT3468-1/LT3468-2 are designed to charge photoflash capacitors quickly and efficiently. The operation 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 VIN for this to happen.

During this phase, current is delivered to the photoflash capacitor via the secondary and diode D1. As the secondary current decreases to zero, the SW pin voltage will begin 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.

Output voltage detection is accomplished via R2, R1, Q2, and comparator A2 (V

Comparator). Resistors R1 and

OUT

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,

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

no longer rises. When CHARGE is brought high

OUT

again, charging resumes. When the target V

voltage is

OUT

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.

LT3468-2

= 3.6V

= 50µF

OUT

100V/DIV

DONE

5V/DIV

CHARGE

5V/DIV

1s/DIV

Figure 2. Halting the Charging Cycle with the CHARGE Pin

3468 F02

WUU

APPLICATIO S I FOR ATIO

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 accomplish 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 voltage as it changes the amplitude of the reflected voltage from the output to the SW pin. Choose N according to the following equation:

+ 2

OUT

31 5.

346812fa

LT3468/LT3468-1/LT3468-2

WUU

APPLICATIO S I FOR ATIO

Where: V 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 formula:

PRI

Where: V the transformer turns ratio. IPK is 1.4 (LT3468), 0.7 (LT3468-1), and 1.0 (LT3468-2).

needs to be equal or larger than this value to ensure

PRI

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 recommended limits as shown in Table 1. A particularly important parameter is the leakage inductance, L power switch of the LT3468/LT3468-1/LT3468-2 turns

Table 1. Recommended Transformer Parameters

PARAMETER NAME LT3468 LT3468-1 LT3468-2 UNITS

PRI

LEAK

N Secondary: Primary Turns Ratio 8 to 12 8 to 12 8 to 12

ISO

SAT

PRI

SEC

is the desired output voltage. The number

OUT

. Choose L

PRI

••

≥

OUT

200 10

OUT

•

is the desired output voltage. N is

Primary Inductance >5 >10 >7 µH

Primary Leakage Inductance 100 to 300 200 to 500 200 to 500 nH

Secondary to Primary Isolation Voltage >500 >500 >500 V

Primary Saturation Current >1.6 >0.8 >1.0 A

Primary Winding Resistance <300 <500 <400 mΩ

Secondary Winding Resistance <40 <80 <60 Ω

according to the following

PRI

−

. When the

LEAK

off, the leakage inductance on the primary of the transformer 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 specification, 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 maximum rating of the SW pin is not exceeded. Make sure to check the SW voltage waveform with V

near the target

OUT

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 magnetic 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.

TYPICAL RANGE TYPICAL RANGE TYPICAL RANGE

VIN = 5V V

= 320V

OUT

10V/DIV

100ns/DIV

Figure 3. LT3468 SW Voltage Waveform

3468 G18

“B”

“A”

Figure 4. New Transformer Design Check (Not to Scale).

MUST BE LESS THAN 50V

MUST BE LESS THAN 40V

3420 F07

346812fa

LT3468/LT3468-1/LT3468-2

WUU

APPLICATIO S I FOR ATIO

Table 2. Pre-Designed Transformers - Typical Specifications Unless Otherwise Noted.

SIZE L

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

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)

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

PRI LPRI-LEAKAGE

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.

PK SEC−

For the circuit of Figure 6 with VIN of 5V, V I

is 137mA. The GSD2004S dual silicon diode is

PK-SEC

recommended for most LT3468/LT3468-1/LT3468-2

Output Diode Selection

The rectifying diode(s) should be low capacitance type with sufficient reverse voltage and forward current ratings. The peak reverse voltage that the diode(s) will see is approximately:

applications. Another option is to use the BAV23S dual silicon diodes. Diodes Incorporated makes a dual diode named MMBD3004S which also meets all the requirements. Table 3 shows the various diodes and relevant specifications. Use the appropriate number of diodes to achieve the necessary reverse breakdown voltage.

VVNV

PK R OUT IN−

•

()

SW Pin Clamp Diode Selection

The peak current of the diode is simply:

The diode D2 in Figure 6 is needed to clamp the SW node.

PK SEC−

14.

(LT3468)

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

PK SEC−

10.

(LT3468-2)

going too far below ground. The diode is required for proper operation of the circuit. The recommended diode

PRI

07.

SEC

(LT3468-1)

852-2489-8266 (ph)

kijimahk@netvigator.com (email)

www.components.tdk.com

0426-56-6262 (ph)

www.tokyo-coil.co.jp

is 371V and

PK-R

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

346812fa

LT3468/LT3468-1/LT3468-2

WUU

APPLICATIO S I FOR ATIO

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.

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

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 breakdown 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.

•

PRIMARY

SECONDARY

•

(DUAL DIODE)

PHOTOFLASH

CAPACITOR

OUT

DONE

CHARGE

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.

TYPICAL APPLICATIO S

2.5V TO 8V

DONE DONE

CHARGE

C1: 4.7µF, X5R OR X7R, 10V T1: KIJIMA MUSEN PART# SBL-5.6-1, L D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES D2: ZETEX ZHCS400 OR EQUIVALENT R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

100k

4.7µF

LT3468

CHARGE

1:10.2

GND

= 10µH, N = 10.2

PRI

320V

OUT

PHOTOFLASH CAPACITOR

3468 F06

3468 F05

Figure 5. Suggested Layout: Keep Electrical Path Formed by C1, Transformer Primary and LT3468/LT3468-1/LT3468-2 Short

2.5V TO 8V

DONE DONE

CHARGE

C1: 4.7µF, X5R OR X7R, 10V T1: KIJIMA MUSEN PART# SBL-5.6S-1, L D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES D2: ZETEX ZHCS400 OR EQUIVALENT R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

100k

4.7µF

LT3468-1

CHARGE

1:10.2

GND

= 24µH, N = 10.2

PRI

320V

OUT

PHOTOFLASH CAPACITOR

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

TYPICAL APPLICATIO S

2.5V TO 8V

DONE DONE

LT3468/LT3468-1/LT3468-2

4.7µF

100k

LT3468-2

1:10.2

GND

320V

OUT

PHOTOFLASH CAPACITOR

CHARGE

C1: 4.7µF, X5R OR X7R, 10V T1: TDK LDT565630T-003 L D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES D2: ZETEX ZHCS400 OR EQUIVALENT R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

Figure 8. LT3468-2 Photoflash Charger Uses High Efficiency 3mm Tall Transformer

PACKAGE DESCRIPTIO

0.62 MAX

3.85 MAX

2.62 REF

0.95 REF

CHARGE

= 10.5µH, N = 10.2

PRI

S5 Package

5-Lead Plastic TSOT-23

(Reference LTC DWG # 05-08-1635)

1.22 REF

1.4 MIN

2.80 BSC

1.50 – 1.75 (NOTE 4)

3468 F08

2.90 BSC (NOTE 4)

RECOMMENDED SOLDER PAD LAYOUT

PER IPC CALCULATOR

0.20 BSC

DATUM ‘A’

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

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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

0.09 – 0.20 (NOTE 3)

1.00 MAX

PIN ONE

0.95 BSC

0.80 – 0.90

1.90 BSC

0.30 – 0.45 TYP 5 PLCS (NOTE 3)

0.01 – 0.10

S5 TSOT-23 0302

346812fa

LT3468/LT3468-1/LT3468-2

TYPICAL APPLICATIO S

LT3468 Photoflash Circuit uses Tiny 3mm Tall Transformer

2.5V TO 8V

DONE DONE

CHARGE

C1: 4.7µF, X5R OR X7R, 10V T1: TDK PART# LDT565630T-001, L D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES D2: ZETEX ZHCS400 OR EQUIVALENT R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

100k

4.7µF

CHARGE

LT3468

PRI

1:10.4

5, 6

7, 8

GND

= 6µH, N = 10.4

LT3468-1 Photoflash Circuit uses Tiny 3mm Tall Transformer

2.5V TO 8V

DONE DONE

CHARGE

C1: 4.7µF, X5R OR X7R, 10V T1: TDK PART# LDT565630T-002, L D1: VISHAY GSD2004S DUAL DIODE CONNECTED IN SERIES D2: ZETEX ZHCS400 OR EQUIVALENT R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

100k

4.7µF

CHARGE

LT3468-1

PRI

1:10.2

GND

= 14.5µH, N = 10.2

OUT

= 50µF

= 20µF

OUT

Charge Time

= 100µF

OUT

VIN (V)

Charge Time

= 50µF

OUT

VIN (V)

3468 TA05

3468 TA06

320V

OUT

PHOTOFLASH CAPACITOR

3468 TA03

320V

OUT

PHOTOFLASH CAPACITOR

3468 TA04

CHARGE TIME (s)

23456789

CHARGE TIME (s)

23456789

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(408) 432-1900 ● FAX: (408) 434-0507

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●

www.linear.com

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LT/TP 0105 1K REV A • PRINTED IN USA

346812fa

LINEAR TECHNOLOGY LT3468, LT3468-1, LT3468-2 Technical data

Specifications and Main Features

Frequently Asked Questions

User Manual