LT3485-0/LT3485-1/

LT3485-2/LT3485-3

11

34850123fb

Note that the absolute maximum rating of the SW pin is

not exceeded. Make sure to check the SW voltage wave-

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 mag-

netic component manufacturers to produce pre-designed

flyback transformers for use with the LT3485-0/LT3485-

1/LT3485-2/LT3485-3. Table 2 shows the details of sev-

eral of these transformers.

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 rat-

ings. The peak reverse voltage that the diode(s) will see is

approximately:

VV

N V

PK R

OUT

IN

)

APPLICATIO S I FOR ATIO

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

TRANSFORMER

SIZE

LPRI-LEAKAGE

FOR USE WITH

NAME

(W

× L × H) mm

(

µH)

(nH)

N

(m

Ω)(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

852-2489-8266 (ph)

kijimahk@netvigator.com (email)

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

(847) 803-6100 (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)

www.tokyo-coil.co.jp

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

Figure 3. LT3485 SW Voltage Waveform

1A/DIV

10A/DIV

100ns/DIV

3485 F03

2

3485 F04

0V

“A”

“B”

MUST BE

LESS THAN 40V

MUST BE

LESS THAN 50V