rt9205 Richtek Technology Corporation, rt9205 Datasheet - Page 14

• Manufacturer Part Number: rt9205
• Description: Dual Regulators - Synchronous Buck Pwm Dc-dc And Linear Controller
• Manufacturer: Richtek Technology Corporation

RT9205/A
The power components and the PWM controller should
be placed firstly. Place the input capacitors, especially the
high-frequency ceramic decoupling capacitors, close to
the power switches. Place the output inductor and output
capacitors between the MOSFETs and the load. Also
locate the PWM controller near by MOSFETs.
A multi-layer printed circuit board is recommended. Figure
13 shows the connections of the critical components in
the converter. Note that the capacitors CIN and COUT
represent numerous physical capacitors. Use a dedicated
grounding plane and use vias to ground all critical
components to this layer. Apply another solid layer as a
power plane and cut this plane into smaller islands of
common voltage levels. The power plane should support
the input power and output power nodes. Use copper filled
polygons on the top and bottom circuit layers for the
PHASE node, but it is not necessary to oversize this
particular island. Since the PHASE node is subjected to
very high dV/dt voltages, the stray capacitance formed
between these islands and the surrounding circuitry will
tend to couple switching noise. Use the remaining printed
circuit layers for small signal routing. The PCB traces
between the PWM controller and the gate of MOSFET
and also the traces connecting source of MOSFETs
should be sized to carry 2A peak currents.
IQ1
IL
V
5V
OUT
Q1
LOAD
IQ2
Q2
GND
VCC
GND
LGATE
RT9205/A
UGATE
FB
Figure 13
www.richtek.com
DS9205/A-09 October 2008
14