LNK603-606/613-616
istic and frequency control for constant current (CC) regulation.
The feedback resistors (R5 and R6) were selected using
standard 1% resistor values to center both the nominal output
voltage and constant current regulation thresholds.
LinkSwitch-II Output Cable Voltage Drop Compensation
BYPASS Pin
Output Voltage
Change Factor
Device
LNK613
Capacitor Value
1.035
1.055
1.045
1.065
1.050
1.070
1.060
1.090
1 mF
10 mF
1 mF
Key Application Considerations
LNK614
LNK615
LNK616
Output Power Table
10 mF
1 mF
The data sheet maximum output power table (Table 1) repre-
sents the maximum practical continuous output power level
that can be obtained under the following assumed conditions:
10 mF
1 mF
10 mF
1. The minimum DC input voltage is 90 V or higher at 85 VAC
input. The value of the input capacitance should be large
enough to meet these criteria for AC input designs.
2. Secondary output of 5 V with a Schottky rectifier diode.
3. Assumed efficiency of 70%.
4. Discontinuous mode operation (KP >1.3).
5. The part is board mounted with SOURCE pins soldered to a
sufficient area of copper to keep the SOURCE pin tempera-
ture at or below 90 °C.
Table 2. Cable Compensation Change Factor vs Device and BYPASS Pin
Capacitor Value.
The output voltage that is entered into PIXls design spreadsheet
is the voltage at the end of the output cable when the power
supply is delivering maximum power. The output voltage at the
terminals of the supply is the value measured at the end of the
cable multiplied by the output voltage change factor.
LinkSwitch-II Layout Considerations
6. Ambient temperature of 50 °C for open frame designs and
an internal enclosure temperature of 60 °C for adapter
designs.
Circuit Board Layout
LinkSwitch-II is a highly integrated power supply solution that
integrates on a single die, both, the controller and the high
voltage MOSFET. The presence of high switching currents and
voltages together with analog signals makes it especially
important to follow good PCB design practice to ensure stable
and trouble free operation of the power supply. See Figure 5 for
a recommended circuit board layout for LinkSwitch-II.
Note: Higher output power are achievable if an output CC
tolerance > 10% is acceptable, allowing the device to be
operated at a higher SOURCE pin temperature.
Output Tolerance
LinkSwitch-II provides an overall output tolerance (including line,
component variation and temperature) of 5% for the output
voltage in CV operation and 10% for the output current during
CC operation over a junction temperature range of 0 °C to 100 °C
for the P/G package. For the D package (SO8) additional CC
variance may occur due to stress caused by the manufacturing
flow (i.e. solder-wave immersion or IR reflow). A sample power
supply build is recommended to verify production tolerances for
each design.
When designing a printed circuit board for the LinkSwitch-II
based power supply, it is important to follow the following
guidelines:
Single Point Grounding
Use a single point (Kelvin) connection at the negative terminal of
the input filter capacitor for the LinkSwitch-II SOURCE pin and
bias winding return. This improves surge capabilities by
returning surge currents from the bias winding directly to the
input filter capacitor.
BYPASS Pin Capacitor Selection
For LinkSwitch-II 60x Family of Devices (without output
cable voltage drop compensation)
Bypass Capacitor
The BYPASS pin capacitor should be located as close as
possible to the SOURCE and BYPASS pins.
A 1 mF BYPASS pin capacitor is recommended. The capacitor
voltage rating should be greater than 7 V. The capacitor’s
dielectric material is not important but tolerance of capacitor
should be ≤ 50%. The capacitor must be physically located
close to the LinkSwitch-II BYPASS pin.
Feedback Resistors
Place the feedback resistors directly at the FEEDBACK pin of
the LinkSwitch-II device. This minimizes noise coupling.
Thermal Considerations
For LinkSwitch-II 61x Family of Devices (with output cable
voltage drop compensation)
The copper area connected to the SOURCE pins provides the
LinkSwitch-II heat sink. A good estimate is that the LinkSwitch-II
will dissipate 10% of the output power. Provide enough copper
area to keep the SOURCE pin temperature below 90 °C. Higher
temperatures are allowable only if an output current (CC)
tolerance above 10% is acceptable. In this case a maximum
SOURCE pin temperature below 110 °C is recommended to
provide margin for part to part RDS(ON) variation.
The amount of output cable compensation can be selected with
the value of the BYPASS pin capacitor. A value of 1 mF selects
the standard cable compensation. A 10 mF capacitor selects
the enhanced cable compensation. Table 2 shows the amount
of compensation for each LinkSwitch-II device and capacitor
value. The capacitor can be either ceramic or electrolytic but
tolerance and temperature variation should be ≤ 50%.
5
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