LM3677TLX-ADJ National Semiconductor Corporation, LM3677TLX-ADJ Datasheet - Page 16

• Manufacturer Part Number: LM3677TLX-ADJ
• Description: 3mhz, 600ma Miniature Step-down Dc-dc Converter For Ultra Low Voltage Circuits
• Manufacturer: National Semiconductor Corporation

www.national.com
4.7 µF for C
10 µF for C
OUTPUT CAPACITOR SELECTION
A ceramic output capacitor of 10 µF, 6.3V is sufficient for most
applications. Use X7R or X5R types; do not use Y5V. DC bias
characteristics of ceramic capacitors must be considered
when selecting case sizes like 0603 and 0805. DC bias char-
acteristics vary from manufacturer to manufacturer and dc
bias curves should be requested from them as part of the ca-
pacitor selection process.
The minimum output capacitance to guarantee good per-
formance is 5.75µF at 2.5V dc bias including tolerances
and over ambient temperature range. The output filter ca-
pacitor smoothes out current flow from the inductor to the
load, helps maintain a steady output voltage during transient
load changes and reduces output voltage ripple. These ca-
pacitors must be selected with sufficient capacitance and
sufficiently low ESR to perform these functions.
The output voltage ripple is caused by the charging and dis-
charging of the output capacitor and by the R
calculated as:
Voltage peak-to-peak ripple due to capacitance can be ex-
pressed as follows
Micro SMD PACKAGE ASSEMBLY AND USE
Use of the Micro SMD package requires specialized board
layout, precision mounting and careful re-flow techniques, as
detailed in National Semiconductor Application Note 1112.
Refer to the section "Surface Mount Technology (SMD) As-
sembly Considerations". For best results in assembly, align-
ment ordinals on the PC board should be used to facilitate
placement of the device. The pad style used with Micro SMD
package must be the NSMD (non-solder mask defined) typ.
This means that the solder-mask opening is larger than the
pad size. This prevents a lip that otherwise forms if the solder-
mask and pad overlap, from holding the device off the surface
of the board and interfering with mounting. See Application
Note 1112 for specific instructions how to do this. The 5-Bump
GRM21BR60J475
GRM21BR60J106
C1608X5R0J475
C2012X5R0J475
C1608X5R0J106
C2012X5R0J106
JMK212BJ475
JMK212BJ106
MIPSA2520D 1R0
BRL2518T1R0M
LQM2HP 1R0
Model
OUT
IN
Model
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
TABLE 2. Suggested Capacitors and Their Suppliers
Type
TABLE 1. Suggested Inductors and Their Suppliers
Taiyo Yuden
Vendor
Murata
FDK
ESR
and can be
Taiyo-Yuden
Taiyo-Yuden
Vendor
muRata
muRata
TDK
TDK
TDK
TDK
16
Voltage peak-to-peak ripple due to ESR can be expressed as
follows
V
Because these two components are out of phase the rms (root
mean squared) value can be used to get an approximate val-
ue of peak-to-peak ripple.
Voltage peak-to-peak ripple,rms can be expressed as follow:
Note that the output voltage ripple is dependent on the induc-
tor current ripple and the equivalent series resistance of the
output capacitor (R
The R
dependent); make sure the value used for calculations is at
the switching frequency of the part.
package used for LM3677 has 300 micron solder balls and
requires 10.82 mils pads for mounting on the circuit board.
The trace to each pad should enter the pad with a 90° entry
angle to prevent debris from being caught in deep corners.
Initially, the trace to each pad should be 7 mil wide, for a sec-
tion approximately 7 mil long or longer, as a thermal relief.
Then each trace should neck up or down to its optimal width.
The important criteria is symmetry. This ensures the solder
bumps on the LM3677 re-flow evenly and that the device sol-
ders level to the board. In particular, special attention must be
paid to the pads for bumps A1 and A3, because GND and
V
quate thermal relief can result in late or inadequate re-flow of
these bumps.
Dimensions LxWxH(mm)
PP-ESR
IN
are typically connected to large copper planes, inade-
2.5 x 2.0 x 0.95
2.5 x 2.0 x 1.2
ESR
2.5x 1.8 x 1.2
= (2 * I
is frequency dependent (as well as temperature
Voltage Rating
RIPPLE
ESR
6.3V
6.3V
6.3V
6.3V
6.3V
6.3V
6.3V
6.3V
) * R
).
ESR
0603 (1608)
0805 (2012)
0805 (2012)
0805 (2012)
0603 (1608)
0805 (2012)
0805 (2012)
0805 (2012)
Case Size
Inch (mm)
D.C.R (max)
100 mΩ
100 mΩ
80 mΩ