Datasheet

V
PP-RMS
= V
PP-C
2
+ V
PP-ESR
2
V
PP-C
=
4*f*C
I
RIPPLE
LM3671
LM3671Q
www.ti.com SNVS294Q –NOVEMBER 2004–REVISED NOVEMBER 2013
Table 2. Suggested Inductors and Their Suppliers
Model Vendor Dimensions LxWxH(mm) D.C.R (max)
DO3314-222MX Coilcraft 3.3 x 3.3 x 1.4 200 mΩ
LPO3310-222MX Coilcraft 3.3 x 3.3 x 1.0 150 mΩ
ELL5GM2R2N Panasonic 5.2 x 5.2 x 1.5 53 mΩ
CDRH2D14NP-2R2NC Sumida 3.2 x 3.2 x 1.55 94 mΩ
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 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 minimum output capacitance to specify good performance is 5.75 µF at 1.8V dc bias including
tolerances and over ambient temperature range. 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 functions.
The output voltage ripple is caused by the charging and discharging of the output capacitor and by the R
ESR
and
can be calculated as:
Voltage peak-to-peak ripple due to capacitance can be expressed as follow:
(9)
Voltage peak-to-peak ripple due to ESR can be expressed as follow:
V
PP-ESR
= (2 * I
RIPPLE
) * R
ESR
Because these two components are out of phase the rms (root mean squared) value can be used to get an
approximate value of peak-to-peak ripple.
The peak-to-peak ripple voltage, rms value can be expressed as follow:
(10)
Note that the output voltage ripple is dependent on the inductor current ripple and the equivalent series
resistance of the output capacitor (R
ESR
).
The R
ESR
is frequency dependent (as well as temperature dependent); make sure the value used for calculations
is at the switching frequency of the part.
Table 3. Suggested Capacitors and Their Suppliers
Case Size
Model Type Vendor Voltage Rating
Inch (mm)
4.7 µF for C
IN
C2012X5R0J475K Ceramic, X5R TDK 6.3V 0805 (2012)
JMK212BJ475K Ceramic, X5R Taiyo-Yuden 6.3V 0805 (2012)
GRM21BR60J475K Ceramic, X5R Murata 6.3V 0805 (2012)
C1608X5R0J475K Ceramic, X5R TDK 6.3V 0603 (1608)
10 µF for C
OUT
GRM21BR60J106K Ceramic, X5R Murata 6.3V 0805 (2012)
JMK212BJ106K Ceramic, X5R Taiyo-Yuden 6.3V 0805 (2012)
C2012X5R0J106K Ceramic, X5R TDK 6.3V 0805 (2012)
C1608X5R0J106K Ceramic, X5R TDK 6.3V 0603 (1608)
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