RT9202_07 Datasheet, PDF (13/14 Pages) Richtek Technology Corporation – Single Synchronous Buck PWM DC-DC Controller

There are two sets of critical components in a DC-DC
converter using the RT9202. The switching power
components are most critical because they switch large
amounts of energy, and as such, they tend to generate
5V
equally large amounts of noise. The critical small signal
components are those connected to sensitive nodes or
those supplying critical bypass current.
GND
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 10 shows the connections of the critical
components in the converter. Note that the capacitors
CIN and COUT each of them represents 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 island 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.
RT9202
IQ1
IL
Q1
IQ2
Q2
V_OUT
LOAD
LGATE VCC GND
UGATE
RT9202
FB
Figure 10
DS9202-09 March 2007
www.richtek.com
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