LTC3586-2 Datasheet, PDF (34/36 Pages) –

LTC3586-2/LTC3586-3
APPLICATIONS INFORMATION
Furthermore, due to its high frequency switching circuitry,
it is imperative that the input capacitors, inductors and
output capacitors be as close to the LTC3586-2/LTC3586-3
as possible and that there be an unbroken ground plane
under the LTC3586-2/LTC3586-3 and all of its external
high frequency components. High frequency currents,
such as the V_BUS, V_IN1, V_IN2, V_IN3, V_OUT3, and V_OUT4
currents on the LTC3586-2/LTC3586-3, tend to find their
way along the ground plane in a myriad of paths ranging
from directly back to a mirror path beneath the incident
path on the top of the board. If there are slits or cuts
in the ground plane due to other traces on that layer,
the current will be forced to go around the slits. If high
frequency currents are not allowed to flow back through
their natural least-area path, excessive voltage will build
up and radiated emissions will occur. There should be a
group of vias under the grounded backside of the pack-
age leading directly down to an internal ground plane. To
minimize parasitic inductance, the ground plane should
be on the second layer of the PC board.
The GATE pin for the external ideal diode controller has
extremely limited drive current. Care must be taken to
minimize leakage to adjacent PC board traces. 100nA of
leakage from this pin will introduce an offset to the 15mV
ideal diode of approximately 10mV. To minimize leakage,
the trace can be guarded on the PC board by surrounding
it with V_OUT connected metal, which should generally be
less that one volt higher than GATE.
358623 F11
Figure 11. Higher Frequency Ground Currents Follow Their
Incident Path. Slices in the Ground Plane Cause High Voltage
and Increased Emmisions
358623f
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