LNK302P POWERINT [Power Integrations, Inc.], LNK302P Datasheet - Page 5

• Manufacturer Part Number: LNK302P
• Description: Lowest Component Count, Energy Efficient Off-Line Switcher IC
• Manufacturer: POWERINT [Power Integrations, Inc.]

Figure 6. Recommended Printed Circuit Layout for LinkSwitch-TN in a Buck Converter Configuration.
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 kΩ.
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
mostly discontinuous conduction mode (MDCM) and continuous
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
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
7) The part is board mounted with SOURCE pins soldered
*KRP is the ratio of ripple to peak inductor current.
INPUT
Optimize hatched copper areas (
input capacitance should be large enough to meet this
criterion.
MDCM operation and for CCM operation, a diode with
t
to a sufficient area of copper to keep the SOURCE pin
temperature at or below 100 °C.
AC
rr
≤35 ns is used.
RF1
D4
D1
C4
) for heatsinking and EMI.
rr
≤75 ns is used for
L2
C5
D
S
S
LinkSwitch-TN
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
provides the lowest cost and highest efficiency converter. CCM
designs require a larger inductor and ultra-fast (t
freewheeling diode in all cases. It is lower cost to use a larger
LinkSwitch-TN in MDCM than a smaller LinkSwitch-TN in CCM
because of the additional external component costs of a CCM
design. However, if the highest output current is required, CCM
should be employed following the guidelines below.
Topology Options
LinkSwitch-TN can be used in all common topologies, with or
without an optocoupler and reference to improve output voltage
tolerance and regulation. Table 2 provide a summary of these
configurations. For more information see the Application
Note – LinkSwitch-TN Design Guide.
Component Selection
Referring to Figure 5, the following considerations may be
helpful in selecting components for a LinkSwitch-TN design.
Freewheeling Diode D1
Diode D1 should be an ultra-fast type. For MDCM, reverse
recovery time t
70 °C or below. Slower diodes are not acceptable, as continuous
mode operation will always occur during startup, causing high
leading edge current spikes, terminating the switching cycle
prematurely, and preventing the output from reaching regulation.
If the ambient temperature is above 70 °C then a diode with
t
For CCM an ultra-fast diode with reverse recovery time
t
rr
rr
≤35 ns should be used.
≤35 ns should be used. A slower diode may cause excessive
FB
BP
S
S
rr
C1
≤75 ns should be used at a temperature of
R3
R1
C3
D1
LNK302/304-306
L1
D2
C2
PI-3750-083004
3/05
rr
OUTPUT
G
≤35 ns)
DC
+
5