NN31001A Datasheet, PDF (30/36 Pages) Panasonic Semiconductor – 7 A Synchronous DC-DC Step down Regulator,

Doc No. TA4-EA-06262
Revision. 2
Product Standards
NN31001A
APPLICATIONS INFORMATION (Continued)
2. Layout Recommendations
Board layout considerations are needed for stable
operation of the DC-DC regulator. It is recommended to
follow the below notes of caution when designing the
board layout.
(a) The Input capacitor C_IN is recommended to be
placed in such a way that the loop (1) in the right
figure becomes minimum in order to suppress the
switching noise.
(b) A single point ground connection (2) is recommended
for the connection of PGND and AGND to improve
operation stability.
(c) Output current line I_OUT and the output sense line
VOUTM is recommended to have small common
impedance to reduce output load variations.
Output sense line VOUTM must be close to the
output capacitor C_O as indicated by (3) in the right
figure.
(d) Power Loss and output ripple voltage can be reduced
by placing the output capacitor C_O so that the
parasitic inductance and the impedance of loop (4)
in the right figure becomes minimum.
This is achieved by reducing the distance between
output capacitor C_O and (2) / (3).
(e) Thick lines in the right figure represent lines with
large current flow. These lines should be designed
as thick as possible.
(f) VFB / SS / VREG lines should be placed far away
from LX, BST pins to reduce the influence of
switching noise. These lines should be designed as
short as possible. This is especially true for the VFB
line, which is a high impedance line.
(g) R_FB1 / R_FB2 should also be placed as far away as
possible from LX, BST pins to minimize the influence
of switching noise. R_FB1 / R_FB2 should be placed close
to the VFB pin.
AVIN
VOUTM
R_FB1
R_FB2
VFB
AGND
PVIN
VOUT
PGND
(1)
(3)
I_OUT
C_IN
C_O
(4)
(2)
Figure : Application circuit diagram
Note : The application circuit diagram and layout diagram
explained in this section, should be used as reference
examples. The operation of the mass production set is
not guaranteed. Sufficient evaluation and verification is
required in the design of the mass production set. The
Customer is fully responsible for the incorporation of
the above illustrated application circuit and the
information attached with it, in the design of the
equipment.
Established : 2014-07-03
Revised : 2014-07-08
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