Datasheet

EN
G
ND
S
W
GND
EN
POST
PIN
The light shaded area is the top surface ground. C , C , Feedback R
and C grounds all come to this area which is as far away from the SW pin
as possible to avoid the noise created at the SW pin.
Note that the top and bottom GND sides are kept away from the SW pin to
avoid picking up noise from the SW pin which swings from GND to V .
OUT IN
IN
EN post pin is connected to EN with a bottom side trace to
maintain unbroken ground plane on top of board
C
OUT
C
IN
R1_fb
C1_fb
R2_fb
C2_fb
L1
EN,GND,V ,FB,SW are
the pads for the SOT-23-5
package
IN
FB
As many through holes
as possible here to
connect the top and
bottom ground planes
V
IN
S
W
V
OUT
The V , SW, V traces,
C , C traces & pads
should be thick - they are
high current paths
IN OUT
IN OUT
Bottom surface - the darker
shaded area is all GND EXCEPT
for area around SW to avoid
picking up switch noise.
If possible put the feedback Rs and Cs on the back side so the C
GND can move closer to the IC GND
OUT
SW node is switching
between V and GND at
1 MHz - VERY NOISY! -
keep all GNDs and GND
planes away!
IN
LM3670
SNVS250E –NOVEMBER 2004–REVISED FEBRUARY 2013 www.ti.com
Table 3. Adjustable LM3670 Configurations for Various V
OUT
VOUT (V) R1 (KΩ) R2 (KΩ) C1 (pF) C2 (pF) L (µH) CIN (µF) COUT (µF)
0.7 80.6 200 200 150 4.7 4.7 10
0.8 120 200 130 none 4.7 4.7 10
0.9 160 200 100 none 4.7 4.7 10
1.0 200 200 82 none 4.7 4.7 10
1.1 240 200 68 none 4.7 4.7 10
1.2 280 200 56 none 4.7 4.7 10
1.24 300 200 56 none 4.7 4.7 10
1.24 221 150 75 120 4.7 4.7 10
1.5 402 200 39 none 10 4.7 10
1.6 442 200 39 none 10 4.7 10
1.7 487 200 33 none 10 4.7 10
1.875 549 200 30 none 10 4.7 14.7
(1)
2.5 806 200 22 82 10 4.7 22
(1) (10 || 4.7)
Board Layout Considerations
PC board layout is an important part of DC-DC converter design. Poor board layout can disrupt the performance
of a DC-DC converter and surrounding circuitry by contributing to EMI, ground bounce, and resistive voltage loss
in the traces. These can send erroneous signals to the DC-DC converter IC, resulting in poor regulation or
instability.
Figure 25. Board Layout Design Rules for the LM3670
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