LT3468/LT3468-1

8

34681i

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

SIZE

LPRI-LEAKAGE

FOR USE WITH

TRANSFORMER NAME

(W

× L × H) mm

(

µH)

(nH)

N

(m

Ω)(Ω)

VENDOR

LT3468

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

(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

0426-56-6336 (ph)

www.tokyo-coil.co.jp

All other parameters need to meet or exceed the recom-

mended limits as shown in Table 1. A particularly impor-

power switch of the LT3468/LT3468-1 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 speci-

fication, which assumes that the current in the power NPN

is zero. Figure 4 shows the SW voltage waveform for the

circuit of Figure 1(LT3468). Note that the absolute maxi-

mum rating of the SW pin is not exceeded. Figure 5 shows

the SW voltage waveform for the circuit of Figure 2(LT3468-

1). Again, the absolute maximum rating of the SW pin is

not compromised. Make sure to check the SW voltage

is the worst case condition for SW voltage.

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.

Table 2 shows the details of several of these transformers.

Figure 4. LT3468 SW Voltage Waveform

Figure 5. LT3468-1 SW Voltage Waveform

APPLICATIO S I FOR ATIO

3468 G18

100ns/DIV

10V/DIV

3468 G19

100ns/DIV

10V/DIV