LTC3558_15 Datasheet, PDF (29/32 Pages) Linear Technology – Linear USB Battery Charger with Buck and Buck-Boost Regulators

LTC3558
APPLICATIONS INFORMATION
Buck-Boost Switching Regulator Input/Output
Capacitor Selection
Low ESR (equivalent series resistance) ceramic capacitors
should be used at both the buck-boost regulator input
(PV_IN2) and the output (V_OUT2). It is recommended that the
input be bypassed with a 10μF capacitor. The output should
be bypassed with at least a 10μF capacitor if using Type I
compensation and 22μF if using Type III compensation.
The same selection criteria apply for the buck-boost
regulator input and output capacitors as described in the
Buck Switching Regulator Input/Output Capacitor Selec-
tion section.
PCB Layout Considerations
In order to deliver maximum charge current under all
conditions, it is critical that the backside of the LTC3558
be soldered to the PC board ground.
The LTC3558 has dual switching regulators. As with all
switching regulators, care must be taken while laying out
a PC board and placing components. The input decoupling
capacitors, the output capacitor and the inductors must all
be placed as close to the pins as possible and on the same
side of the board as the LTC3558. All connections must
also be made on the same layer. Place a local unbroken
ground plane below these components. Avoid routing
noisy high frequency lines such as those that connect to
switch pins over or parallel to lines that drive high imped-
ance inputs.
3558f
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