RT8005 RICHTEK [Richtek Technology Corporation], RT8005 Datasheet - Page 10

• Manufacturer Part Number: RT8005
• Description: 1A, 2MHz, High-Efficiency Synchronous Buck PWM Converter
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT8005
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
2.2 F/4.7 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 RT8005.
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 (PVDD and PGND).
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 RT8005.
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
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
C2
R5
C3
R3
2, 3
Figure 3. Bottom Layer
4
5
8
Figure 2. Top Layer
PVDD
VDD
EN
GND
RT8005
Figure 1
COMP
PGND
V
IN
FB
LX
DS8005-08 August 2007
1
6
7
9, 10
L1
R4
C4
R2
R1
C1
V
OUT