LM3670MFX-2.5 National Semiconductor, LM3670MFX-2.5 Datasheet - Page 14

• Manufacturer Part Number: LM3670MFX-2.5
• Description: Miniature Step-Down DC-DC Converter for Ultra Low Voltage Circuits
• Manufacturer: National Semiconductor

www.national.com
Application Information
OUTPUT CAPACITOR SELECTION
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 ripple current can be calculated as:
Voltage peak-to-peak ripple due to capacitance =
Voltage peak-to-peak ripple due to ESR =
VOUT (V)
1.875
10 µF for C
VJ1812V106MXJAT
4.7 µF for C
VJ1812V475MXJAT
1.24
1.24
C3216X5R0J475M
LMK432BJ106MM
EMK325BJ475MN
JMK325BJ106MM
0.7
0.8
0.9
1.0
1.1
1.2
1.5
1.6
1.7
2.5
IDC2512NB100M
CDRH5D18-100
DO1608C-103
ELL6RH100M
Model
Model
OUT
IN
R1 (KΩ)
80.6
120
160
200
240
280
300
221
402
442
487
549
806
TABLE 3. Adjustable LM3670 Configurations for Various V
R2 (KΩ)
TABLE 2. Suggested Capacitors and Their Suppliers
TABLE 1. Suggested Inductors and Their Suppliers
Ceramic
Ceramic
Ceramic
Ceramic
Ceramic
Ceramic
200
200
200
200
200
200
200
150
200
200
200
200
200
Type
(Continued)
Panasonic
Coilcraft
Vendor
Sumida
Vishay
C1 (pF)
200
130
100
82
68
56
56
75
39
39
33
30
22
Taiyo-Yuden
Taiyo-Yuden
Taiyo-Yuden
Vendor
Vishay
Vishay
TDK
14
C2 (pF)
Voltage peak-to-peak ripple, root mean squared =
Note that the output ripple is dependent on the current ripple
and the equivalent series resistance of the output capacitor
(R
Because these two components are out of phase the rms
value is used. The R
temperature dependent); make sure the frequency of the
R
frequency.
none
none
none
none
none
none
none
none
none
none
150
120
ESR
82
ESR
408-727-2500
847-639-6400
714-373-7366
847-956-0666
).
given is the same order of magnitude as the switching
Phone
L (µH)
408-727-2500
847-925-0888
847-925-0888
408-727-2500
847-925-0888
847-803-6100
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
10
10
10
10
10
Phone
ESR
is frequency dependent (as well as
OUT
CIN (µF)
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
408-330-4098
847-639-1469
714-373-7323
847-956-0702
408-330-4098
847-925-0899
847-925-0899
408-330-4098
847-925-0899
847-803-6296
FAX
Note: (10 || 4.7)
COUT (µF)
FAX
14.7
10
10
10
10
10
10
10
10
10
10
10
22