rt9201 Richtek Technology Corporation, rt9201 Datasheet - Page 12

• Manufacturer Part Number: rt9201
• Description: High Efficiency Step-down Dc-dc Converter
• Manufacturer: Richtek Technology Corporation

Output Capacitor Selection
The capacitor's ESR determines the output ripple voltage
and the initial voltage drop following a high slew-rate
transient's edge. Typically, if the ESR requirement is
satisfied, the capacitance is adequate to filtering. The
output ripple voltage can be calculated as:
The ceramic capacitor with low ESR value provides the
low output ripple and low size profile. Connect a 22 F
ceramic capacitor at output terminal for good performance
and place the input and output capacitors as close as
possible to the device.
Layout Considerations
Follow the PCB layout guidelines for optimal performance
of RT9201.
1. For the main current paths as indicated in bold lines in
2. Put the input capacitor as close as possible to the
3. LX node is with high frequency voltage swing and
4. Connect feedback network behind the output
5. Connect all analog grounds to a command node and
6. An example of 2-layer PCB layout is shown in
www.richtek.com
12
RT9201
Figure 3, keep their traces short and wide.
device pins (PVDD and PGND).
should be kept small area. Keep analog components
away from LX node to prevent stray capacitive noise
pick-up.
capacitors. Keep the loop area small. Place the
feedback components near the RT9201.
then connect the command node to the power ground
behind the output capacitors.
Figure 4 to Figure 6 for reference.
ΔV
OUT
R3
Figure 3. RT9201 Layout Diagram
ΔI
10
1
9
4
5
C
EN
VDD
NC
NC
GND
C1
R2
(ESR
RT9201
FB
3
PGND
PVDD
8
SS
LX
R1
C2
C
8
7
6
2
OUT
C4
1
L1
f
OSC
C9
C7
)
C6
V
V
DD
OUT
Preliminary
Figure 6. Silkscreen Layer
Figure 5. Bottom Layer
Figure 4. Top Layer
DS9201-04 August 2004