2-5

LNK302/304-306

5

Rev. I 11/08

Figure 6a. Recommended Printed Circuit Layout for LinkSwitch-TN in a Buck Converter Configuration using P or G Package.

cycles are skipped. To provide overload protection if no cycles

are skipped during a 50 ms period, LinkSwitch-TN will enter

auto-restart (LNK304-306), limiting the average output power

to approximately 6% of the maximum overload power. Due to

tracking errors between the output voltage and the voltage across

C3 at light load or no load, a small pre-load may be required

(R4). For the design in Figure 5, if regulation to zero load is

required, then this value should be reduced to 2.4 k

Ω.

Key Application Considerations

LinkSwitch-TN Design Considerations

Output Current Table

Data sheet maximum output current table (Table 1) represents

the maximum practical continuous output current for both

mostlydiscontinuousconductionmode(MDCM)andcontinuous

conduction mode (CCM) of operation that can be delivered from

a given LinkSwitch-TN device under the following assumed

conditions:

1) Buck converter topology.

2) The minimum DC input voltage is ≥70 V. The value of

input capacitance should be large enough to meet this

criterion.

3) For CCM operation a KRP* of 0.4.

4) Output voltage of 12 VDC.

5) Efficiency of 75%.

6) A catch/freewheeling diode with t

MDCM operation and for CCM operation, a diode with

t

7) The part is board mounted with SOURCE pins soldered

to a sufficient area of copper to keep the SOURCE pin

temperature at or below 100

°C.

*KRP is the ratio of ripple to peak inductor current.

LinkSwitch-TN Selection and Selection Between

MDCM and CCM Operation

Select the LinkSwitch-TN device, freewheeling diode and output

inductor that gives the lowest overall cost. In general, MDCM

+

PI-3750-121106

C2

L1

L2

R1

R3

RF1

D3

D4

D2

D1

C1

C3

C5

C4

Optimize hatched copper areas (

) for heatsinking and EMI.

D

S

S

FB

BP

S

S

LinkSwitch-TN

AC

INPUT

DC

OUTPUT

Figure 6b. Recommended Printed Circuit Layout for LinkSwitch-TN in a Buck Converter Configuration using D Package

to Bottom Side of the Board.

AC

INPUT

+

DC

OUTPUT

PI-4546-011807

Optimize hatched copper areas (

) for heatsinking and EMI.

S

S

S

S

BP

FB

D1

C2

R3

RF1

D3

D4

D2

R1

C1

C4

C5

C3

L2

L1

D