RT8120 查看數據表（PDF） - Richtek Technology
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RT8120 Datasheet PDF : 17 Pages
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RT8120
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance, θJA. The derating curves in Figure 7 allow the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
3.6
Four-Layer PCB
3.2
SOP-8 (Exposed Pad)
2.8
2.4
2.0
1.6
1.2
0.8 SOP-8
0.4
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 7. Derating Curve of Maximum Power Dissipation
Layout Considerations
Layout planning plays a critical role in modern high-
frequency switching converter design. Circuit boards with
good layout can help the IC function properly and achieve
low losses, low switching noise, and stable operation with
improved performance. Without a good layout, the PCB
could radiate excessive noise, causing noise-induced IC
problems and converter instability. The following guidelines
is suggested have better IC performance.
` The power components should be placed first. Keep the
connection between power components as short as
possible.
` Input bulk capacitors should be placed close to the drain
of the high side MOSFET and the source of the low
side MOSFET.
` Place the VCC bypass capacitor as close as possible to
the RT8120.
` Minimize the trace length between the power MOSFETs
and its drivers.
Since the drivers use short, high current pulses to drive
the power MOSFETs, the driving traces should be as
short and wide as possible to reduce the trace
inductance. This is especially true for the low side
MOSFET, since this can reduce the possibility of the
shoot through.
` Provide enough copper area around the power MOSFETs
and the inductors to aid in heat sinking. Using thick
copper PCB can also reduce the resistance and
inductance to improve efficiency.
` The bank of the output capacitor should be placed
physically close to the load. This can minimize the
impedance seen by the load and then improve the
transient response.
` Placing all the high frequency decoupling ceramic
capacitors close to their decoupling targets.
` Small-signal components should be located as close
as possible to the IC. The small signal components
include the feedback components, current sensing
components, compensation components, function
setting components and any bypass capacitors.
These components belong to the high impedance circuit
loop and are inherently sensitive to noise pick-up.
Therefore, they must be located close to their respective
controller pins and away from the noisy switching nodes.
` A multi-layer PCB design is recommended. Make use
of one single layer as the power ground and have a
separate control signal ground as the reference of all
signals.
Copyright ©2013 Richtek Technology Corporation. All rights reserved.
DS8120-08 September 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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