Datasheet LT3485-0, LT3485-1, LT3485-2, LT3485-3 Datasheet (LINEAR TECHNOLOGY)

查询LT3485-0供应商

Monitor and Integrated IGBT Drive

FEATURES

■

Integrated IGBT Driver

■

Voltage Output Monitor

■

Uses Small Transformers: 5.8mm × 5.8mm × 3mm

■

Operates from Two AA Batteries, Single Cell Li-Ion
or Any Supply from 1.8V up to 16V

■

No Output Voltage Divider Needed

■

No External Schottky Diode Required

■

Charges Any Size Photoflash Capacitor

■

Available in 10-Lead (3mm × 3mm) DFN

Fast Charge Time

VERSION INPUT CURRENT (mA) CHARGE TIME (sec)

LT3485-3 750 2.5

LT3485-0 500 3.7

LT3485-2 350 5.5

LT3485-1 225 4.0*

VIN = V
100µF capacitor, 320V. *50µF capacitor

BAT

= 3.6V

U

APPLICATIO S

■

Digital Camera and Cell Phone Flash Charger

LT3485-0/LT3485-1/

LT3485-2/LT3485-3

Photoflash Capacitor

Chargers with Output Voltage

U

DESCRIPTIO

®

The LT
grated ICs containing complete charger and IGBT drive
functions. The patented control technique of the LT3485-x
allows it to use extremely small transformers. Output voltage
detection requires no external circuitry. The turns ratio of the
transformer controls the final charge voltage. While charging,
the output voltage on the capacitor may be monitored by a
microcontroller from the monitor pin. Each device contains an
on-chip high voltage NPN power switch, which can withstand
negative voltages on the switch pin without an external
Schottky diode. The device features a V
the use of two AA cells to charge the capacitor. The internal
circuitry operates from the VIN pin. The LT3485-0 has a
primary current limit of 1.4A, whereas the LT3485-3, LT3485-2,
and LT3485-1 have current limits of 2A, 1A and 0.7A respec­tively. These different current limits result in tightly controlled
input currents.

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 LT3485
series of parts are housed in a leadless (3mm × 3mm) DFN
package.

All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 6636021.

3485 family of photoflash chargers are highly inte-

pin, which allows

BAT

, LTC and LT are registered trademarks of Linear Technology Corporation.

U

TYPICAL APPLICATIO

LT3485-0 Photoflash Charger Uses High Efficiency 3mm Tall Transformers

DANGER HIGH VOLTAGE – OPERATION BY HIGH VOLTAGE TRAINED PERSONNEL ONLY

V

BAT

2 AA OR

1 TO 2 Li-Ion

V

CC

5V

0.22µF

4.7µF

V

BAT

DONE

CHARGE

LT3485-0

V

IN

IGBTPWR

IGBTIN

SW

GND

V

MONT

IGBTOUT

1

2

1:10.2

•

•

4

5

TO
MICRO

320V

150µF
PHOTOFLASH
CAPACITOR

1M

2.2µF
600V

TRIGGER

1

2

3

3485 TA01

T

A

FLASHLAMP

C

IGBT

V

OUT

50V/DIV

AVERAGE

INPUT CURRENT

0.5A/DIV

LT3485-0 Charging Waveform

VIN = 3.6V

= 100µF

C

OUT

1s/DIV

3485 TA02

34850123f

1

LT3485-0/LT3485-1/
LT3485-2/LT3485-3

WW

W

U

ABSOLUTE AXI U RATI GS

(Note 1)

VIN Voltage .............................................................. 10V

Voltage ............................................................ 10V

V

BAT

SW Voltage ................................................... –1V to 50V

SW Pin Negative Current ...................................... –0.5A

CHARGE Voltage...................................................... 10V

IGBTIN Voltage ........................................................ 10V

IGBTOUT Voltage ..................................................... 10V

DONE Voltage .......................................................... 10V

IGBTPWR Voltage.................................................... 10V

V

Voltage ......................................................... 10V

MONT

Current into DONE Pin ...............................0.2mA/–1mA

Maximum Junction Temperature .......................... 125°C

Operating Temperature Range (Note 2) ... –40°C to 85°C

Storage Temperature Range ..................–65°C to 125°C

UUW

PACKAGE/ORDER I FOR ATIO

TOP VIEW

CHARGE

EXPOSED PAD (11) IS GND, MUST BE SOLDERED TO PCB

1

V

2

BAT

V

IN

SW

SW

10-LEAD (3mm ´ 3mm) PLASTIC DFN

T

11

3

4

5

DD PACKAGE

= 125°C θJA = 43°C/W

JMAX

ORDER PART NUMBER

LT3485EDD-0
LT3485EDD-1
LT3485EDD-2
LT3485EDD-3

Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF

Lead Free Part Marking: http://www.linear.com/leadfree/

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

10

V

MONT

DONE

9

IGBTPWR

8

7

IGBTIN

6

IGBTOUT

DD PART MARKING

LBRH
LBVN
LBVP

LBTK

ELECTRICAL CHARACTERISTICS

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

PARAMETER CONDITIONS MIN TYP MAX UNITS

Quiescent Current Not Switching 5 8 mA

VIN Voltage Range
V

Voltage Range

BAT

Switch Current Limit LT3485-3 1.6 1.7 1.8 A

Switch V

CESAT

V

Comparator Trip Voltage Measured as VSW – V

OUT

V

Comparator Overdrive 300ns Pulse Width 200 400 mV

OUT

DCM Comparator Trip Voltage Measured as VSW – V
CHARGE Pin Current V

The ● denotes the specifications which apply over the full operating

= V

BAT

= 0V 0 1 µA

V

CHARGE

LT3485-0 1.1 1.2 1.3 A
LT3485-2 0.75 0.85 0.95 A
LT3485-1 0.45 0.55 0.65 A

LT3485-3, I
LT3485-0, I
LT3485-2, I
LT3485-1, I

CHARGE

V

CHARGE

= 1.5A 310 400 mV

SW

= 1A 210 300 mV

SW

= 700mA 170 225 mV

SW

= 400mA 100 175 mV

SW

IN

IN

= 3V 65 100 µA
= 0V 0 0.1 µA

= 3V, unless otherwise noted.

CHARGE

●

●

●

●

2.5 10 V

1.7 10 V

31 31.5 32 V

10 45 120 mV

2

34850123f

LT3485-0/LT3485-1/

LT3485-2/LT3485-3

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

PARAMETER CONDITIONS MIN TYP MAX UNITS

Switch Leakage Current V
CHARGE Input Voltage High
CHARGE Input Voltage Low
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 140 200 mV

DONE Leakage Current V
IGBT Input Voltage High
IGBT Input Voltage Low
IGBT Output Rise Time C
IGBT Output Fall Time C
V

Monitor Accuracy SW – V

OUT

Monitor Output Current 200 µA

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

The ● denotes the specifications which apply over the full operating

= 25°C. VIN = V

A

= V

= 5V, in Shutdown

IN

SW

= 3V, DONE NPN Off 20 100 nA

DONE

= 4000pF, IGBTPWR = 5V, 10%→90% 200 270 320 ns

OUT

= 4000pF, IGBTPWR = 5V, 90%→10% 130 180 230 ns

OUT

= 20V 610 625 640 mV

BAT

SW – V

= 30V 920 940 960 mV

BAT

= V

BAT

Note 2: The LTC3485E-X is 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.

= 3V, unless otherwise noted.

CHARGE

●

●

●

●

●

0.01 1 µA

1V

0.3 V

1.5 V

0.3 V

34850123f

3

LT3485-0/LT3485-1/

V

OUT

50V/DIV

0.5s/DIVV

IN

= 3.6V

C

OUT

= 50µF

3485 G03

AVERAGE

INPUT

CURRENT

0.5A/DIV

V

OUT

(V)

0

INPUT CURRENT (mA)

400

500

600

150 250

3485 G06

300

200

50 100

200 300

100

0

2.5V

3.6V

4.2V

V

OUT

(V)

0

0

INPUT CURRENT (mA)

100

300

400

500

200

900

3485 G09

200

100

50

250 300

150

600

700

800

2.5V

3.6V

4.2V

LT3485-2/LT3485-3

UW

TYPICAL PERFOR A CE CHARACTERISTICS

curves use the circuit of Figure 9, LT3485-2 use the circuit of Figure 10 and LT3485-3 use the circuit of Figure 11 unless otherwise noted.

LT3485-0 curves use the circuit of Figure 8, LT3485-1

V

OUT

50V/DIV

AVERAGE

INPUT

CURRENT

1A/DIV

V

OUT

50V/DIV

AVERAGE

INPUT

CURRENT

1A/DIV

LT3485-0 Charging Waveform

C

= 3.6V

IN
OUT

= 50µF

0.5s/DIVV

3485 G01

AVERAGE

CURRENT

LT3485-1 Charging Waveform

V

OUT

50V/DIV

INPUT

0.5A/DIV
C

= 3.6V

IN
OUT

= 50µF

LT3485-3 Charging Waveform Charge Time

6

LT3485-1

5

4

3

2

CHARGE TIME (SECONDS)

1

0

LT3485-0

2

3

C

= 3.6V

IN
OUT

= 50µF

0.5s/DIVV

3485 G04

0.5s/DIVV

C

OUT

LT3485-2

LT3485-3

456

VIN (V)

LT3485-2 Charging Waveform

3485 G02

LT3485-0 Input Current

= 50µF

78

1635 G05

4

LT3485-1 Input Current LT3485-2 Input Current LT3485-3 Input Current

250

200

150

100

INPUT CURRENT (mA)

50

0

050

100

200

150

V

(V)

OUT

250

2.5V

3.6V

4.2V

300

3485 G07

400

300

200

INPUT CURRENT (mA)

100

0

0

50 100 150 200

2.5V

3.6V

4.2V

V

(V)

OUT

250 300

3485 G08

34850123f

LT3485-0/LT3485-1/

V

OUT

(V)

50

40

EFFICIENCY (%)

50

60

70

80

90

100

150 200 250

3485 G12

300

2.5V

3.6V

4.2V

TEMPERATURE (°C)

–40 –20

0

CURRENT LIMIT (mA)

800

2000

0

40

60

3485 G18

400

1600

1200

20

80

100

LT3485-3

LT3485-0

LT3485-2

LT3485-1

LT3485-2/LT3485-3

UW

TYPICAL PERFOR A CE CHARACTERISTICS

curves use the circuit of Figure 9, LT3485-2 use the circuit of Figure 10 and LT3485-3 use the circuit of Figure 11 unless otherwise noted.

LT3485-0 Efficiency LT3485-1 Efficiency LT3485-2 Efficiency

90

90

LT3485-0 curves use the circuit of Figure 8, LT3485-1

80

70

60

EFFICIENCY (%)

50

40

50

100

LT3485-3 Efficiency

90

80

70

60

EFFICIENCY (%)

50

40

50

100

150 200 250

V

(V)

OUT

150 200 250

V

(V)

OUT

2.5V

3.6V

4.2V

300

3485 G10

2.5V

3.6V

4.2V

300

3485 G13

80

70

60

EFFICIENCY (%)

50

40

50

150 200 250

100

V

LT3485-0 Output Voltage

322

321

320

(V)

OUT

V

319

318

317

2

456

3

VIN (V)

OUT

(V)

2.5V

3.6V

4.2V

300

3485 G11

–40°C
25°C
85°C

78

3485 G14

LT3485-1 Output Voltage

322

321

320

(V)

OUT

V

319

318

317

2

456

3

–40°C
25°C
85°C

78

VIN (V)

3485 G15

328

327

326

(V)

325

OUT

V

324

323

322

LT3485-2 Output Voltage LT3485 Switch Current Limits

–40°C
25°C
85°C

2

456

3

VIN (V)

78

3485 G16

LT3485-3 Output Voltage

322

321

320

(V)

OUT

V

319

318

317

2

456

3

VIN (V)

–40°C
25°C
85°C

78

3485 G17

34850123f

5

LT3485-0/LT3485-1/
LT3485-2/LT3485-3

UW

TYPICAL PERFOR A CE CHARACTERISTICS

curves use the circuit of Figure 9, LT3485-2 use the circuit of Figure 10 and LT3485-3 use the circuit of Figure 11 unless otherwise noted.

LT3485-0 curves use the circuit of Figure 8, LT3485-1

LT3485-0 Switching Waveform

V

SW

10V/DIV

I

PRI

1A/DIV

V

= 3.6V

IN
OUT

= 100V

1µs/DIVV

LT3485-3 Switching Waveform

V

SW

10V/DIV

I

PRI

2A/DIV

VIN = 3.6V

= 100V

V

OUT

1µs/DIV

LT3485-2 Switching Waveform

V

SW

10V/DIV

I

PRI

1A/DIV

V

= 3.6V

IN
OUT

= 300V

1µs/DIVV

3485 G19

3485 G22

3485 G25

LT3485-1 Switching Waveform

V

SW

10V/DIV

I

PRI

1A/DIV

= 100V

V

OUT

1µs/DIVVIN = 3.6V

LT3485-0 Switching Waveform

V

SW

10V/DIV

I

PRI

1A/DIV

V

= 3.6V

IN
OUT

= 300V

1µs/DIVV

LT3485-3 Switching Waveform

V

SW

10V/DIV

I

PRI

2A/DIV

VIN = 3.6V

= 300V

V

OUT

1µs/DIV

3485 G26

3485 G20

3485 G23

LT3485-2 Switching Waveform

V

SW

10V/DIV

I

PRI

1A/DIV

V

= 3.6V

IN
OUT

= 100V

1µs/DIVV

LT3485-1 Switching Waveform

V

SW

10V/DIV

I

PRI

1A/DIV

V

= 3.6V

IN
OUT

= 300V

1µs/DIVV

LT3485-0/LT3485-1/LT3485-2/
LT3485-3 Switch Breakdown
Voltage

10

SW PIN IS RESISTIVE UNTIL BREAKDOWN
VOLTAGE DUE TO INTEGRATED

9

RESISTORS. THIS DOES NOT INCREASE

8

QUIESCENT CURRENT OF PART

7

6

5

4

3

SWITCH CURRENT (mA)

2

1

0

0 102030405060708090100

SWITCH VOLTAGE (V)

T = 25°C

T = –40°C

VIN = V

T = 85°C

CHARGE

3485 G21

3485 G24

= 5V

3485 G27

6

34850123f

LT3485-0/LT3485-1/

LT3485-2/LT3485-3

U

UU

PI FU CTIO S

CHARGE (Pin 1): Charge Pin. A low (<0.3V) to high (>1V)
transition on this pin puts the part into power delivery
mode. Once the target voltage is reached, the part will stop
charging the output. Toggle this pin to start charging
again. Bringing the pin low (<0.3V) will terminate the
power delivery and put the part in shutdown.

V

(Pin 2): Battery Supply Pin. Must be locally bypassed

BAT

with a good quality ceramic capacitor. Battery supply
must be 1.7V or higher.

V

(Pin 3): Input Supply Pin. Must be locally bypassed

IN

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

SW (Pins 4, 5): 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:

IGBTOUT (Pin 6): Output Drive for IGBT Gate. Connect
this pin to the gate of the IGBT.

IGBTIN (Pin 7): Logic Input Pin for IGBT Drive. When this
pin is driven higher than 1.5V, the IGBT output pin goes
high. When the pin is below 0.3V, the output is low.

IGBTPWR (Pin 8): Input Supply Pin. Must be locally
bypassed with a good quality ceramic capacitor. Input
supply must be 0.1V higher than the turn-on voltage for
the IGBT.

DONE (Pin 9): Open NPN Collector Indication Pin. When
target output voltage is reached, NPN turns on. This pin
needs a pull-up resistor or current source.

V

(Pin 10): Supplies a voltage proportional to the

MONT

output voltage where 1V is the end of charge voltage. Only
valid while the part is charging.

Exposed Pad (Pin 11): Ground. Tie directly to local
ground plane.

N

=

where V

V

+ 2

OUT

31 5.

is the desired output voltage.

OUT

34850123f

7

LT3485-0/LT3485-1/
LT3485-2/LT3485-3

UU

W

FU CTIO AL BLOCK DIAGRA

TO BATTERY

CHIP

POWER

ENABLE

COMPARATOR

LT3485-3: R
LT3485-0: R
LT3485-2: R
LT3485-1: R

C1

R3
4k

+

A2

OUT

–

SENSE
SENSE
SENSE
SENSE

V

CHARGE

TO V

IGBTON

TO V

IN

C2

DONE

9 10 3 2

Q3

ONE-

1

SHOT

IGBT
DRIVER

8

IN

7

DRIVER

POWER

IGBT

6

TO GATE OF IGBT

QQ

SR

20Ω

20k

V

MONT

SAMPLE

AND HOLD

R1

2.5k

1.25V

REFERENCE

ONE­SHOT

= 0.010Ω
= 0.015Ω
= 0.022Ω
= 0.030Ω

D1

T1

PRIMARY

R2

60k

R4

Q2

120k

ONE-

SHOT

DCM

COMPARATOR

+

A3

SW
4, 5

SECONDARY

V

OUT

C

OUT

PHOTOFLASH
CAPACITOR

–

+

60mV

–

DRIVER

S

RQ

Q1

+

R

–

+

20mV

SENSE

–

GND

11

3485 F01

A1

8

Figure 1

34850123f

OPERATIO

LT3485-0/LT3485-1/

LT3485-2/LT3485-3

U

The LT3485-0/LT3485-1/LT3485-2/LT3485-3 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 2A
(LT3485-3), 1.4A (LT3485-0), 1A (LT3485-2) or 0.7A
(LT3485-1), 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 60mV higher than V

for this to happen.

BAT

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 60mV above
V

or lower, the output of A3 (DCM Comparator) will go

BAT

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
V

, the output of A2 goes high which resets the master

BAT

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

V

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.

Both V

and VIN have undervoltage lockout (UVLO).

BAT

When one of these pins goes below its UVLO voltage, the
DONE pin goes low. With an insufficient bypass capacitor
on V

or VIN, the ripple on the pin is likely to activate

BAT

UVLO and terminate the charge. The applications circuits
in the data sheet suggest values adequate for most
applications.

The LT3485 V

pin functions as an output to a

MONT

microcontroller to communicate the progress of the charge.
The V

pin starts to function at about 0.2V, which

MONT

corresponds to 64V with a turns ratio of 10.2. When the
V

pin is at 1V, the DONE pin goes low and the

MONT

charging terminates. The pin’s output is only valid when
the part is charging.

The LT3485 also integrates an IGBT drive. The IGBTPWR
pin supplies the power. The IGBT output goes high when
IGBTIN goes high and conversely goes low when IGBTIN
goes low. While IGBTIN is low, the IGBT drive draws no
quiescent current from IGBTPWR.

V

OUT

100V/DIV

V

DONE

5V/DIV

V

CHARGE

5V/DIV

LT3485-2

= 3.6V

V

IN

= 50µF

C

OUT

Figure 2. Halting the Charging Cycle with the CHARGE Pin

1s/DIV

3485 F02

34850123f

9

LT3485-0/LT3485-1/

L

V

NI

PRI

OUT

PK

≥

−

••

•

200 10

9

LT3485-2/LT3485-3

U

WUU

APPLICATIO S I FOR ATIO

Choosing the Right Device
(LT3485-0/LT3485-1/LT3485-2/LT3485-3)

The only difference between the four versions of the
LT3485 is the peak current level. For the fastest possible
charge time, use the LT3485-3. The LT3485-1 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 LT3485-1 can
use a physically smaller transformer. The LT3485-0 and
LT3485-2 have a current limit in between that of the
LT3485-3 and the LT3485-1.

Transformer Design

The flyback transformer is a key element for any
LT3485-0/LT3485-1/LT3485-2/LT3485-3 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 LT3485-0/LT3485-1/LT3485-2/LT3485­3 accomplish output voltage detection by monitoring the
flyback waveform on the SW pin. When the SW voltage
reaches 31.5V higher than the V
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:

V

+ 2

OUT

N

=

31 5.

voltage, the part will

BAT

where V

is the desired output voltage. The number 2

OUT

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

. Choose L

PRI

according to the following

PRI

formula:

where V
former turns ratio. I

is the desired output voltage. N is the trans-

OUT

is 1.4 (LT3485-0), 0.7 (LT3485-1),

PK

1 (LT3485-2) and 2 (LT3485-3).

L

needs to be equal or larger than this value to ensure

PRI

that the LT3485-0/LT3485-1/LT3485-2/LT3485-3 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

. When the

LEAK

power switch of the LT3485-0/LT3485-1/LT3485-2/
LT3485-3 turns 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 8 (LT3485-0).

Table 1. Recommended Transformer Parameters

TYPICAL RANGE TYPICAL RANGE TYPICAL RANGE TYPICAL RANGE

PARAMETER NAME LT3485-0 LT3485-1 LT3485-2 LT3485-3 UNITS

L

PRI

L

LEAK

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

ISO

I

SAT

R

PRI

R

SEC

10

Primary Inductance >5 >10 >7 >3.5 µH
Primary Leakage Inductance 100 to 300 200 to 500 200 to 500 100 to 300 nH

Secondary to Primary Isolation Voltage >500 >500 >500 >500 V
Primary Saturation Current >1.6 >0.8 >1.0 >2 A
Primary Winding Resistance <300 <500 <400 <200 mΩ
Secondary Winding Resistance <40 <80 <60 <30 Ω

34850123f

LT3485-0/LT3485-1/

VVNV

PK R OUT IN−

=+(• )

LT3485-2/LT3485-3

U

WUU

APPLICATIO S I FOR ATIO

Note that the absolute maximum rating of the SW pin is
not ex

ceeded. Make sure to check the SW voltage wave­form with V
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
affect 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 LT3485-0/LT3485­1/LT3485-2/LT3485-3. Table 2 shows the details of sev­eral of these transformers.

10A/DIV

near the target output voltage, as this is the

OUT

I

PRI

1A/DIV

2

V

SW

Capacitor Selection

For the input bypass capacitors, high quality X5R or X7R
types 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 rat­ings. The peak reverse voltage that the diode(s) will see is
approximately:

“B”

“A”

V

SW

MUST BE
LESS THAN 50V

MUST BE
LESS THAN 40V

0V

= 5V

V

IN

= 320V

V

OUT

Figure 3. LT3485 SW Voltage Waveform

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

FOR USE WITH NAME (W × L × H) mm (µH) (nH) N (mΩ)(Ω) VENDOR

LT3485-0/LT3485-2 SBL-5.6-1 5.6 × 8.5 × 4.0 10 200 Max 10.2 103 26 Kijima Musen
LT3485-1 SBL-5.6S-1 5.6 × 8.5 × 3.0 24 400 Max 10.2 305 55 Hong Kong Office

LT3485-0 LDT565630T-001 5.8 × 5.8 × 3.0 6 200 Max 10.4 100 Max 10 Max TDK
LT3485-1 LDT565630T-002 5.8 × 5.8 × 3.0 14.5 500 Max 10.2 240 Max 16.5 Max Chicago Sales Office
LT3485-2 LDT565630T-003 5.8 × 5.8 × 3.0 10.5 550 Max 10.2 210 Max 14 Max [phone] (ph)
LT3485-3 LDT565630T-041 5.8 × 5.8 × 3.0 4.7 150 Max 10.4 90 Max 6.4 Max www.components.tdk.com

LT3485-0/LT3485-1 T-15-089 6.4 × 7.7 × 4.0 12 400 Max 10.2 211 Max 27 Max Tokyo Coil Engineering
LT3485-1 T-15-083 8.0 × 8.9 × 2.0 20 500 Max 10.2 675 Max 35 Max Japan Office
LT3485-3 T-17-109A 6.5 × 7.9 × 4.0 5.9 300 Max 10.2 78 Max 18.61 Max 0426-56-6262 (ph)

100ns/DIV

TRANSFORMER SIZE L

3485 F03

PRI LPRI-LEAKAGE

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

R

PRI

R

SEC

[e-mail] (email)

3485 F04

852-2489-8266 (ph)

www.tokyo-coil.co.jp

34850123f

11

LT3485-0/LT3485-1/
LT3485-2/LT3485-3

U

WUU

APPLICATIO S I FOR ATIO

The peak current of the diode is simply:

I=

PK-SEC

I=

PK-SEC

I=

PK-SEC

I=

PK-SEC

F

or the circuit of Figure 8 with V

and I

PK-SEC

is recommended for most LT3485-0/LT3485-1/LT3485­2/LT3485-3 applications. Another option is to use the
BAV23S dual silicon diodes. Table 3 shows the various
diodes and relevant specifications. Use the appropriate
number of diodes to achieve the necessary reverse break­down voltage.

2

LT3485-3

()

N

1.4
LT3485-0

(

))

N

1

LT3485-2

()

N

0.7

LT3485-

()

11

N

of 5V, V

BAT

PK-R

is 371V

is 137mA. The GSD2004S dual silicon diode

V

IN = 5V

V

OUT = 320V

IGBT Drive

The IGBT is a high current switch for the 100A+ current
through the photoflash lamp. To create a redeye effect or
to adjust the light output, the lamp current needs to be
stopped, or quenched, with an IGBT before discharging
the photoflash capacitor fully. The IGBT device also con­trols the 4kV trigger pulse required to ionize the xenon gas
in the photoflash lamp. Figure 5 is a schematic of a fully
functional photoflash application with the LT3485 serving
as the IGBT drive. An IGBT drive charges the gate capaci­tance to start the flash. The IGBT drive does not need to
pull-up the gate fast because of the inherently slow nature
of the IGBT. A rise time of 2µs is sufficient to charge the
gate of the IGBT and create a trigger pulse. With slower
rise times, the trigger circuitry will not have a fast enough
edge to create the required 4kV pulse. The fall time of the
IGBT drive is critical to the safe operation of the IGBT. The
IGBT gate is a network of resistors and capacitors, as
shown in Figure 6. When the gate terminal is pulled low,

Table 3. Recommended Output Diodes

PART (V) (mA) (pF) VENDOR

GSD2004S 2x300 225 5 Vishay
(Dual Diode) [phone]

BAV23S 2x250 225 5 Philips Semiconductor
(Dual Diode) [phone]

MMBD3004S 2x350 225 5 Diodes Inc
(Dual Diode) [phone]

MAX REVERSE VOLTAGE MAX FORWARD CONTINUOUS CURRENT CAPACITANCE

V

BAT

2 AA OR

1 TO 2 Li-Ion

V

CC

5V

0.22µF

4.7µF

DONE

CHARGE

V

IGBTPWR

IGBTIN

V

BAT

IN

LT3485-0

IGBTOUT

V

SW

GND

MONT

1

2

1:10.2

•

•

4

5

TO
MICRO

320V

150µF
PHOTOFLASH
CAPACITOR

1M

2.2µF
600V

TRIGGER

1

2

3

T

3485 F05

www.vishay.com

www.philips.com

www.diodes.com

A

FLASHLAMP

C

IGBT

12

Figure 5. Complete Xenon Circuit

34850123f

LT3485-0/LT3485-1/

LT3485-2/LT3485-3

U

WUU

APPLICATIO S I FOR ATIO

GATE

3485 F06

EMITTER

Figure 6. IGBT Gate

the capacitance closest to the terminal goes low but the
capacitance further from the terminal remains high. This
causes a small portion of the device to handle the full 100A
of current, which quickly destroys the device. The pull
down circuitry needs to pull down slower than the internal
RC time constant in the gate of the IGBT. This is easily
accomplished with a resistor in series with the IGBT drive,
which is integrated into the LT3485.

The LT3485’s integrated drive circuit is independent of the
charging function. The IGBT section draws its power from
the IGBTPWR pin. The rise and fall times are measured
using a 4000pF output capacitor. The typical 10% to 90%

rise time is 270ns. The drive pulls high to IGBTPWR. The
typical 90% to 10% fall time is 180ns. The drive pulls
down to 300mV. The IGBT driver pulls a peak of 150mA
when driving an IGBT and 2mA of quiescent current. In the
low state, the IGBT’s quiescent current is less than 0.1µA.

Table 4 is a list of recommended IGBT devices for strobe
applications. These three devices are all packaged in
8-lead TSSOP packages.

V

Monitor

OUT

The voltage output monitor is a new feature to monitor the
progress of capacitor charging with a microcontroller.
The monitor uses the flyback waveform to output a
voltage proportional to the output of the flyback converter.
The output monitor voltage range for the pin is 0V to 1V.
The 1V output corresponds with the charge cycle termi­nating and the DONE pin going low. The voltage output
monitor is only functional when the circuit is charging
(DONE and CHARGE are high.)

Table 4. Recommended IGBTs

DRIVE BREAKDOWN COLLECTOR

VOLTAGE VOLTAGE CURRENT

PART (V) (V) (PULSED) (A) VENDOR

CY25BAH-8F 2.5 400 150 Renesas
CY25BAJ-8F 4 400 150 [phone]

www.renesas.com

GT8G133 4 400 150 Toshiba Semiconductor

[phone]

www.semicon.toshiba.co.jp/eng/

34850123f

13

LT3485-0/LT3485-1/
LT3485-2/LT3485-3

U

WUU

APPLICATIO S I FOR ATIO

Board Layout

The high voltage operation of the LT3485-0/LT3485-1/
LT3485-2/LT3485-3 demands careful attention to board
layout. You will not get advertised performance with
careless layout. Figure 7 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

CHARGE

C2 C3

•

C

OUT

PHOTOFLASH

CAPACITOR

V

IN

+

SECONDARY PRIMARY

T1

•

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 LT3485-0/LT3485-1/
LT3485-2/LT3485-3 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.

1 10

3

5

C1

V

MONT

92

811

74

6

3485 F07

R1

DONE

IGBTPWR

IGBTIN

IGBTOUT

D1

(DUAL DIODE)

V

BAT

Figure 7. Suggested Layout: Keep Electrical Path Formed by C1,
Transformer Primary and LT3485-0/LT3485-1/LT3485-2/LT3485-3 Short

14

34850123f

TYPICAL APPLICATIO S

1.8V TO 8V

V

IN

2.5V TO 8V

U

T1

D1

TO MICRO

TO GATE OF IGBT

SW

GND

V

MONT

= 10µH, N = 10.2

PRI

1:10.2

3485 F08

V

BAT

C1

4.7µF

R1

V

BAT

100k

DONE

CHARGE

C2

0.22µF

C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6-1, L
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

DONE

CHARGE

LT3485-0

V

IN

IGBTPWR

IGBTIN

IGBTOUT

LT3485-0/LT3485-1/

LT3485-2/LT3485-3

320V

C

OUT

PHOTOFLASH
CAPACITOR

Figure 8. LT3485-0 Photoflash Charger Uses High Efficiency 4mm Tall Transformer

T1

D1

TO MICRO

TO GATE OF IGBT

320V

C

OUT

PHOTOFLASH
CAPACITOR

V

2.5V TO 8V

V

SW

GND

MONT

PRI

1:10.2

3485 F09

= 24µH, N = 10.2

V

BAT

1.8V TO 8V

DONE

CHARGE

IN

C2

0.22µF

C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6S-1, L
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

C1

4.7µF

R1
100k

V

BAT

DONE

CHARGE

LT3485-1

V

IN

IGBTPWR

IGBTIN

IGBTOUT

Figure 9. LT3485-1 Photoflash Charger Uses High Efficiency 3mm Tall Transformer

34850123f

15

LT3485-0/LT3485-1/
LT3485-2/LT3485-3

U

TYPICAL APPLICATIO S

1.8V TO 8V

CHARGE

V

IN

2.5V TO 8V

C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: KIJIMA MUSEN PART# SBL-5.6-1, L
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

V

DONE

BAT

C2

0.22µF

C1

4.7µF

R1
100k

V

BAT

DONE

CHARGE

LT3485-2

V

IN

IGBTPWR

IGBTIN

SW

GND

VMONT

IGBTOUT

= 10µH, N = 10.2

PRI

T1

1:10.2

TO MICRO

TO GATE OF IGBT

3485 F10

D1

320V

C

OUT

PHOTOFLASH
CAPACITOR

Figure 10. LT3485-2 Photoflash Charger Uses High Efficiency 4mm Tall Transformer

T1

D1

TO MICRO

TO GATE OF IGBT

320V

C

OUT

PHOTOFLASH
CAPACITOR

V

2.5V TO 8V

V

1:10.2

SW

GND

MONT

3485 F11

V

BAT

1.8V TO 8V

DONE

CHARGE

IN

C2

0.22µF

C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-041, L
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

C1

4.7µF

R1
100k

V

BAT

DONE

CHARGE

LT3485-3

V

IN

IGBTPWR

IGBTIN

= 4.7µH, N = 10.4

PRI

IGBTOUT

Figure 11. LT3485-3 Photoflash Charger Uses High Efficiency 3mm Tall Transformer

16

34850123f

TYPICAL APPLICATIO S

V

IN

2.5V TO 8V

U

T1

D1

TO MICRO

TO GATE OF IGBT

V

MONT

1:10.2

SW

GND

3485 F12

V

BAT

1.8V TO 8V

DONE

CHARGE

C2

0.22µF

C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-001, L
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

C1

4.7µF

V

BAT

DONE

CHARGE

LT3485-0

V

IN

IGBTPWR

IGBTIN

= 6µH, N = 10.4

PRI

IGBTOUT

LT3485-0/LT3485-1/

LT3485-2/LT3485-3

320V

C

OUT

PHOTOFLASH
CAPACITOR

Figure 12. LT3485-0 Photoflash Circuit Uses Tiny 3mm Tall Transformer

6

5

4

3

2

CHARGE TIME (SECONDS)

1

0

2

LT3485-1

LT3485-0

3

456

LT3485-2

LT3485-3

VIN (V)

C

= 50µF

OUT

78

3485 F13

Figure 13. Charge Time with TDK Transformers (Figures 11, 12, 13, 14 and 15)

34850123f

17

LT3485-0/LT3485-1/
LT3485-2/LT3485-3

U

TYPICAL APPLICATIO S

V

IN

2.5V TO 8V

T1

V

BAT

1.8V TO 8V

DONE

CHARGE

C2

0.22µF

C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-002, L
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

C1

4.7µF

V

BAT

DONE

CHARGE

LT3485-1

V

IN

IGBTPWR

IGBTOUT

IGBTIN

= 14.5µH, N = 10.2

PRI

1:10.2

SW

GND

VMONT

D1

TO MICRO

TO GATE OF IGBT

3485 F14

320V

C

OUT

PHOTOFLASH
CAPACITOR

Figure 14. LT3485-1 Photoflash Circuit Uses Tiny 3mm Tall Transformer

T1

D1

TO MICRO

TO GATE OF IGBT

3485 F15

320V

C

OUT

PHOTOFLASH
CAPACITOR

V

2.5V TO 8V

V

BAT

1.8V TO 8V

DONE

CHARGE

IN

C2

0.22µF

C1: 4.7µF, X5R OR X7R, 10V
C2: 0.22µF, X5R or X7R, 10V
T1: TDK LDT565630T-003, L
D1: DIODES INC MMBD3004S DUAL DIODE CONNECTED IN SERIES
R1: PULL UP RESISTOR NEEDED IF DONE PIN USED

C1

4.7µF

V

BAT

DONE

CHARGE

LT3485-2

V

IN

IGBTPWR

IGBTIN

= 10µH, N = 10.2

PRI

IGBTOUT

1:10.2

SW

GND

VMONT

Figure 15. LT3485-2 Photoflash Circuit Uses Tiny 3mm Tall Transformer

18

34850123f

PACKAGE DESCRIPTIO

LT3485-0/LT3485-1/

LT3485-2/LT3485-3

U

DD Package

10-Lead Plastic DFN (3mm × 3mm)

(Reference LTC DWG # 05-08-1699)

0.675 ±0.05

3.50 ±0.05

1.65 ±0.05
(2 SIDES)2.15 ±0.05

PACKAGE
OUTLINE

0.25 ± 0.05

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

PIN 1

TOP MARK

(SEE NOTE 6)

0.200 REF

NOTE:

1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE

0.50
BSC

2.38 ±0.05
(2 SIDES)

3.00 ±0.10
(4 SIDES)

0.75 ±0.05

1.65 ± 0.10
(2 SIDES)

0.00 – 0.05

R = 0.115

TYP

2.38 ±0.10
(2 SIDES)

BOTTOM VIEW—EXPOSED PAD

106

15

0.50 BSC

0.38 ± 0.10

0.25 ± 0.05

(DD10) DFN 1103

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.

34850123f

19

LT3485-0/LT3485-1/
LT3485-2/LT3485-3

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LTC3407 Dual 600mA (I

Converter I

LT3420/LT3420-1 1.4A/1A, Photoflash Capacitor Chargers with Charges 220µF to 320V in 3.7 seconds from 5V,

Automatic Top-Off V

LTC3425 5A ISW, 8MHz, Multi-Phase Synchronous Step-Up DC/DC 95% Efficiency, VIN: 0.5V to 4.5V, V

Converter I

LTC3440 600mA/1A (I

Converter I

LT3468/LT3468-1/ Photoflash Capacitors in ThinSOT™ Charges 110µF to 320V in 4.6 Seconds from 3.6V,
LT3468-2 V

LT3472 Dual ±34V, 1.2MHz Boost (350mA)/Inverting (400mA) Integrated Schottkys, VIN: 2.2V to 16V, V

DC/DC Converter for CCD Bias I

LT3463/LT3463A Dual Boost (250mA)/Inverting (250mA/400mA) Integrated Schottkys, VIN: 2.3V to 15V, V

DC/DC Converter for CCD Bias I

LT3484-0/LT3484-1/ Photoflash Capacitor Chargers Charges 110µF to 320V in 4.6 Seconds from 3.6V,
LT3484-2 V

ThinSOT is a trademark of Linear Technology Corporation.

), 1.5MHz, Synchronous Step-Down DC/DC 96% Efficiency, VIN: 2.5V to 5.5V, V

OUT

), Synchronous Buck-Boost DC/DC 95% Efficiency, VIN: 2.5V to 5.5V, V

OUT

<1µA, MS10E

SD

: 2.2V to 16V, IQ = 90µA, ISD < 1µA, MS10

IN

< 1µA, QFN-32

SD

= 25µA, ISD < 1µA, MS-10 DFN-12

Q

: 2.5V to 16V, IQ = 5mA, ISD < 1µA, ThinSOT

IN

= 2.5mA, ISD < 1µA, DFN

Q

= 40µA, ISD < 1µA, DFN

Q

: 2.5V to 16V, V

IN

2mm × 3mm DFN

: 1.8V to 16V, IQ = 5mA, ISD < 1µA,

BAT

= 0.6V, IQ = 40µA,

OUT(MIN)

= 5.25V, IQ = 12µA,

OUT(MIN)

= 2.5V to 5.5V,

OUT(MIN)

OUT(MAX)

OUT(MAX)

= ±34V,

= ±40V,

20

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone] ● www.linear.com

34850123f

LT/LWI/TP 0805 500 • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 2005