rt8003 Richtek Technology Corporation, rt8003 Datasheet - Page 10

• Manufacturer Part Number: rt8003
• Description: 600ma, 2mhz, High-efficiency Synchronous Buck 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:
Where f
capacitance and I
The ceramic capacitor with low ESR value provides the
low output ripple and low size profile. Connect a 1 F/2.2 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 RT8003.
1. For the main current paths as indicated in bold lines in
Figure 1, keep their traces short and wide.
2. Put the input capacitor as close as possible to the device
pins (VDD and GND).
3. LX node is with high frequency voltage swing and should
be kept small area. Keep analog components away from
LX node to prevent stray capacitive noise pick-up.
4. Connect feedback network behind the output capacitors.
Keep the loop area small. Place the feedback components
near the RT8003.
5.Connect all analog grounds to a command node and
then connect the command node to the power ground
behind the output capacitors.
6. An example of 2-layer PCB layout is shown in Figure 2
to Figure 3 for reference.
www.richtek.com
10
RT8003
V
OUT
OSC
I
C
(ESR
= operating frequency, C
C
=
8
x
I
C
L
OUT
= ripple current in the inductor.
1
x
f
OSC
)
OUT
= output
V
IN
C1
R4
Figure 3. Bottom Layer
VDD
EN
Figure 2. Top Layer
RT8003
GND
Figure 1
COMP
DS8003-03 November 2005
LX
FB
L1
C2
R1
R2
C3
V
OUT