LM3671MFX-1.375 National Semiconductor, LM3671MFX-1.375 Datasheet - Page 14

• Manufacturer Part Number: LM3671MFX-1.375
• Description: 2MHz / 600mA Step-Down DC-DC Converter in SOT23-5
• Manufacturer: National Semiconductor

www.national.com
22 µF for C
10 µF for C
Application Information
OUTPUT CAPACITOR SELECTION
Use a 22 µF, 6.3V ceramic capacitor. Use X7R or X5R types,
do not use Y5V. DC bias characteristics of ceramic capaci-
tors must be considered when selecting case sizes like 0805
and 0603. DC bias characteristics vary from manufacturer to
manufacturer and dc bias curves should be requested from
them as part of the capacitor selection process. The LM3671
has been evaluated with 22 µF, 6.3V, 0805 with worst case
tolerances including dc bias effects. The use of two 10 µF,
6.3V, 0805 caps will give an overall higher capacitance value
when dc bias is considered.
The output filter capacitor 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 capacitors must be selected with sufficient
capacitance and sufficiently low ESR to perform these func-
tions.
The output voltage ripple is caused by the charging and
discharging of the output capacitor and also due to its R
and can be calculated as:
Voltage peak-to-peak ripple due to capacitance can be ex-
pressed as follows
Voltage peak-to-peak ripple due to ESR can be expressed
as follows
V
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
PP-ESR
GRM21BR60J226K
GRM21BR60J106K
C2012X5R0J226K
C2012X5R0J106K
JMK212BJ226K
JMK212BJ106K
LPO3310-222MX
CDRH2D14-2R2
DO3314-222MX
ELL5GM2R2N
= (2 * I
Model
OUT
IN
Model
RIPPLE
)
*
R
ESR
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
Ceramic, X5R
TABLE 2. Suggested Capacitors and Their Suppliers
TABLE 1. Suggested Inductors and Their Suppliers
Type
Panasonic
Coilcraft
Coilcraft
Vendor
Sumida
(Continued)
ESR
Taiyo-Yuden
Taiyo-Yuden
Vendor
Murata
Murata
TDK
TDK
14
Dimensions LxWxH(mm)
Because these two components are out of phase the rms
value can be used to get an approximate value of peak-to-
peak ripple.
Voltage peak-to-peak ripple, root mean squared can be ex-
pressed as follows
Note that the output voltage ripple is dependent on the
inductor 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.
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.
3.2 x 3.2 x 1.55
3.3 x 3.3 x 1.4
3.3 x 3.3 x 1.0
5.2 x 5.2 x 1.5
ESR
is frequency dependent (as well as temperature
Voltage Rating
6.3V
6.3V
6.3V
6.3V
6.3V
6.3V
ESR
).
D.C.R (max)
0805 (2012)
0805 (2012)
0805 (2012)
0805 (2012)
0805 (2012)
0805 (2012)
Inch (mm)
Case Size
200 mΩ
150 mΩ
53 mΩ
94 mΩ