LCS700-708
Figure 7 shows a an example of preferred routing for the
optocoupler and traces connected to the FEEDBACK pin. The
optocoupler is spaced away from the transformer, reducing
noise pickup. The optocoupler output trace (from pin 3) is also
routed to increase the distance between it and “active”
components and traces, such as T1 and the hot side of
capacitor C12. Resistor R20 is located close to U1 rather than
optocoupler U2, so that any noise picked up on the optocoupler
trace is filtered by the combination of R20 and C4 before it gets
to the FEEDBACK pin on U1. C4 is placed directly adjacent to
the FEEDBACK pin of U1 (pin 4).
VCCH is connected to the standby supply through a high-
voltage ultrafast diode and a 2.2
W
resistor connected in series.
This diode resistor network charges the VCCH bypass/storage
capacitor whenever the internal LLC low-side MOSFET is on.
The resistor limits the peak instantaneous charging current.
See R6 and D1 in Figure 8.
G Pin
Figure 5.
Placement of Bypass Capacitors on Signal Pins of IC.
Figure 6.
Alternate Layout for LCS Footprint using Round Pads with Jumper Connecting
Two Grounds Highlighted.
7
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Rev. B 062011
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