BL3406B
1.5 MHz, 800mA Synchronous Buck Converter
frequency. Ceramic capacitors with X5R or
X7R dielectrics are recommended due to
their low ESR and high ripple current. The
output ripple ∆V
OUT
is determined by:
1. The power traces, consisting of the GND
trace, the SW trace and the V
IN
trace
should be kept short, direct and wide.
2. Does the V
FB
pin connect directly to the
feedback resistors? The resistive divider
R1/R2 must be connected between the (+)
plate of Cout and ground.
3. Does the (+) plate of C
IN
connect to V
IN
as
closely as possible? This capacitor
provides the AC current to the internal
power MOSFETS.
4. Keep the switching node, SW, away from
the sensitive V
FB
node.
5. Keep the (-) plates of C
IN
and C
OUT
as
close as possible.
∆
V
OUT
≤
V
OUT
×
(
V
IN
−
V
OUT
)
1
×
ESR
+
V
IN
×
f
OSC
×
L
8
×
f
OSC
×
C
2
Layout Considerations
When laying out the printed circuit board, the
following checklist should be used to ensure
proper operation of the BL3406B. These
items are also illustrated graphically in
Figures 5 and 6. Check the following in your
layout:
2.7V - 4.2V
V
IN
C1
4.7uF
4
V
IN
SW
3
L1
2.2 H
V
OUT
1.8V
C2
10uF
2.7V - 4.2V
V
IN
C1
4.7uF
4
V
IN
SW
3
L1
2.2 H
V
OUT
1.8V
BL3406B-ADJ
1
C3
22pF
BL3406B-18
1
C2
10uF
Run
GND
2
V
FB
5
Run
GND
2
R2
200k
R1
100k
V
OUT
5
Figure 3. BL3406B-ADJ Layout Circuit
Figure 4. BL3406B-1.8 Layout Circuit
Figure 5. BL3406B-ADJ Suggested Layout
Figure 6. BL3406B-1.8 Suggested Layout
PPMIC BU
BL3406B Rev 1.5
10/2009
www.belling.com.cn
Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited
©2009 Belling All Rights Reserved
9
BELLING [ SHANGHAI BELLING CO., LTD. ]
