lnk623 Power Integrations, Inc., lnk623 Datasheet - Page 5

• Manufacturer Part Number: lnk623
• Description: Energy-efficient, Off-line Switcher With Accurate Primary-side Constant-voltage Cv Control
• Manufacturer: Power Integrations, Inc.

Output Regulation
The LNK626 regulates the output using ON/OFF control,
enabling or disabling switching cycles based on the sampled
voltage on the FEEDBACK pin. The output voltage is sensed
using a primary referenced winding on transformer T1 eliminating
the need for an optocoupler and a secondary sense circuit. The
resistor divider formed by R3 and R6 feeds the winding voltage
into U1. Standard 1% resistor values were used to center the
nominal output voltages. Resistor R5 and C5 reduce pulse
grouping by creating an offset voltage that is proportional to the
number of consecutive enabled switching cycles.
Output Power Table
The data sheet maximum output power table (Table 1)
represents the maximum practical continuous output power
level that can be obtained in a Flyback converter under the
following assumed conditions:
1.
2.
3.
4.
5.
6.
7.
Note: Higher output power are achievable if the effi ciency is
higher than 80%, typically for high output voltage designs.
Bypass Pin Capacitor
A 1 μF Bypass pin capacitor (C4) is recommended. The
capacitor voltage rating should be equal to or greater than
6.8 V. The capacitor’s dielectric material is not important. The
capacitor must be physically located close to the
LinkSwitch-CV BYPASS pin.
Circuit board layout
LinkSwitch-CV 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.
www.powerint.com
Key Application Considerations
The minimum DC input voltage is 100 V or higher at 90 VAC
input. The value of the input capacitance should be large
enough to meet these criteria for AC input designs.
Secondary output of 5 V with a Schottky rectifi er diode.
Assumed effi ciency of 80%.
Continuous conduction mode operation (K
Refl ected Output Voltage (V
The part is board mounted with SOURCE pins soldered to a
suffi cient area of copper to keep the SOURCE pin tempera-
ture at or below 110 °C.
Ambient temperature of 50 °C for open frame designs and
an internal enclosure temperature of 60 °C for adapter
designs.
OR
) of 110 V.
P
= 0.4).
When designing a board for the LinkSwitch-CV 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 fi lter capacitor for the LinkSwitch-CV SOURCE pin and
bias winding return. This improves surge capabilities by
returning surge currents from the bias winding directly to the
input fi lter capacitor.
Bypass Capacitor
The BYPASS pin capacitor should be located as close as
possible to the SOURCE and BYPASS pins.
Feedback Resistors
Place the feedback resistors directly at the FEEDBACK pin of
the LinkSwitch-CV device. This minimizes noise coupling.
Thermal Considerations
The copper area connected to the source pins provide the
LinkSwitch-CV heat sink. A rule of thumb estimate is that the
LinkSwitch-CV will dissipate 10% of the output power. Provide
enough copper area to keep the source pin temperature below
110° C to provide margin for part to part R
Secondary Loop Area
To minimize leakage inductance and EMI, the area of the loop
connecting the secondary winding, the output diode and the
output fi lter capacitor should be minimized. In addition,
suffi cient copper area should be provided at the anode and
cathode terminal of the diode for heatsinking. A larger area is
preferred at the quiet cathode terminal. A large anode area can
increase high frequency radiated EMI.
Electrostatic Discharge Spark Gap
In chargers and adapters ESD discharges may be applied to
the output of the supply. In these applications the addition of a
spark gap is recommended. A trace is placed along the
isolation barrier to form one electrode of a spark gap. The other
electrode, on the secondary side, is formed by the output return
node. The arrangement directs ESD energy from the secondary
to the primary side AC input. A 10 mil gap is placed near the
AC input. The gap decouples any noise picked up on the spark
gap trace to the AC input. The trace from the AC input to the
spark gap electrode should be spaced away from other traces
to prevent unwanted arcing occurring and possible circuit
damage.
LNK623-626
DS(ON)
variation.
Rev. C 12/08
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