LTC3586_15 Datasheet, PDF (33/36 Pages) Linear Technology – High Efficiency USB Power Manager with Boost, Buck-Boost and Dual Bucks

LTC3586/LTC3586-1
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/LTC3586-1
as possible and that there be an unbroken ground plane
under the LTC3586/LTC3586-1 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/LTC3586-1, 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 package 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.
3586 F11
Figure 11. Higher Frequency Ground Currents Follow Their
Incident Path. Slices in the Ground Plane Cause High Voltage
and Increased Emmisions
3586fb
33