RT8105 datasheet(11/12 Pages) RICHTEK

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RT8105

DS8105-03 April 2011

www.richtek.com

Placing the ceramic capacitors physically close to the

drain of the high side MOSFET. This can reduce the

input voltage drop when high side MOSFET is turned

on.

Keep the high-current loops as short as possible. The

current transition between MOSFETs usually causes

di/dt voltage spike due to the parasitic components on

PCB trace and component lead. Therefore, making the

trace length between power MOSFETs and inductors

wide and short can reduce the voltage spike and also

reduce EMI.

Make MOSFET gate driver path as short as possible.

Since the gate driver uses high-current pulses to switch

on/off power MOSFET, the driver path must be short to

reduce the trace inductance. This is especially important

for low side MOSFET because this can reduce the

possibility of shoot-through. Besides, also make the

width of gate driving path as wide as possible to reduce

the trace resistance.

Provide enough copper area around power MOSFETs

to help heat dissipation. Using thick copper also

reduces the trace resistance and inductance to have

better performance.

The output capacitors should be placed physically close

to the load. This can minimize the trace parasitic

components and improve transient response.

The feedback voltage divider resistor must be placed

close to FB pin because it is noise-sensitive.

ROCSET should be placed close to IC.

The small signal MOSFET/BJT used to shutdown the

controller should be placed close to IC to minimize the

trace parasitic components.

Voltage feedback path must away from switching

nodes. The switching nodes, such as the

interconnection between high side MOSFET, low side

MOSFET and inductor, is extremely noisy. Feedback

path must away from this kind of noisy node to avoid

noise pick-up.

A multi-layer PCB design is recommended. Use one

single layer as the ground and have separate layers for

power rail or signal.

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