LNK3202/3204-6
4. Thermal check – At maximum output power, minimum input
voltage and maximum ambient temperature, verify that the
LinkSwitch-TN2 SOURCE pin temperature is 100 °C or below.
This ensures adequate margin due to variations in RDS(ON) from
part to part. If the device temperature of the IC exceeds 85 °C
with ambient temperature of 25 °C, it is recommended the next
bigger device in the family should be selected for the application.
A battery powered thermocouple meter is recommended to make
measurements when the SOURCE pins are a switching node.
Alternatively, the ambient temperature may be raised to indicate
margin to thermal shutdown.
Quick Design Checklist
As with any power supply design, all LinkSwitch-TN2 designs should
be verified for proper functionality on the bench. The following
minimum tests are recommended:
1. Adequate DC rail voltage – Check that the minimum DC input
voltage does not fall below 70 VDC at maximum load, minimum
input voltage.
2. Correct Diode Selection – UF400x series diodes with reverse
recovery time of 75 ns or better are recommended only for
designs that operate in MDCM at an ambient of 70 °C or below.
For designs operating in continuous conduction mode (CCM) and/
or higher ambients, then a diode with a reverse recovery time of
35 ns or better, such as the BYV26C, is recommended.
3. Maximum drain current – Verify that the peak drain current is
below the data sheet peak drain specification under worst-case
conditions of highest line voltage, maximum overload (just prior
to auto-restart) and highest ambient temperature.
In a LinkSwitch-TN2 design using a buck or buck-boost converter
topology, the SOURCE pin is a switching node. Oscilloscope measure-
ments should therefore be made with probe grounded to a DC voltage,
such as primary return or DC input rail, and not to the SOURCE pins.
The power supply input must always be supplied from an isolated
source when doing measurements (e.g. via an isolation transformer).
10
Rev. F 01/17
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