LM3674MFX-1.2 National Semiconductor, LM3674MFX-1.2 Datasheet - Page 12

• Manufacturer Part Number: LM3674MFX-1.2
• Description: IC,SMPS CONTROLLER,VOLTAGE-MODE,TSOP,5PIN,PLASTIC
• Manufacturer: National Semiconductor

www.national.com
Application Information
Method 2:
A more conservative and recommended approach is to
choose an inductor that has saturation current rating greater
than the max current limit of 1200 mA.
A 2.2 µH inductor with a saturation current rating of at least
1200 mA is recommended for most applications. The induc-
tor’s resistance should be less than around 0.3Ω for good
efficiency. Table 2 lists suggested inductors and suppliers.
For low-cost applications, an unshielded bobbin inductor is
suggested. For noise critical applications, a toroidal or
shielded-bobbin inductor should be used. A good practice is
to lay out the board with overlapping footprints of both types
• I
• I
• V
• L: min inductor value including worst case tolerances
• f: minimum switching frequency (1.6 MHz)
• V
(30% drop can be considered for method 1)
Ripple
outmax
CDRH2D14NP-2R2NC
IN
OUT
: maximum input voltage in application
LPO3310-222MX
DO3314-222MX
: output voltage
ELL5GM2R2N
: average to peak inductor current
: maximum load current (600mA)
Model
TABLE 2. Suggested Inductors and Their Suppliers
(Continued)
Panasonic
Coilcraft
Coilcraft
Vendor
Sumida
12
for design flexibility. This allows substitution of a low-noise
toroidal inductor, in the event that noise from low-cost bobbin
models is unacceptable.
INPUT CAPACITOR SELECTION
A ceramic input capacitor of 4.7 µF, 6.3V is sufficient for most
applications. Place the input capacitor as close as possible
to the V
improved input voltage filtering. 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. The minimum input capacitance to guarantee
good performance is 2.2µF at 3V dc bias; 1.5µF at 5V dc
bias including tolerances and over ambient temperature
range. The input filter capacitor supplies current to the PFET
switch of the LM3674 in the first half of each cycle and
reduces voltage ripple imposed on the input power source. A
ceramic capacitor’s low ESR provides the best noise filtering
of the input voltage spikes due to this rapidly changing
current. Select a capacitor with sufficient ripple current rat-
ing. The input current ripple can be calculated as:
Dimensions LxWxH(mm)
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
IN
pin of the device. A larger value may be used for
D.C.R (max)
200 mΩ
150 mΩ
53 mΩ
94 mΩ