LCS700-708
Figure 7 shows a an example of preferred routing for the optocou-
pler 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
Rev. G 05/15
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