LM2678S-ADJ/NOPB National Semiconductor, LM2678S-ADJ/NOPB Datasheet - Page 14
LM2678S-ADJ/NOPB
Manufacturer Part Number
LM2678S-ADJ/NOPB
Description
IC REG SIMPLE SWITCHER TO-263-7
Manufacturer
National Semiconductor
Series
SIMPLE SWITCHER®r
Type
Step-Down (Buck)r
Datasheet
1.LM2678SD-3.3NOPB.pdf
(26 pages)
Specifications of LM2678S-ADJ/NOPB
Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
1.2 ~ 37 V
Current - Output
5A
Frequency - Switching
260kHz
Voltage - Input
8 ~ 40 V
Operating Temperature
-40°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
D²Pak, TO-263 (7 leads + tab)
Primary Input Voltage
40V
No. Of Outputs
1
Output Voltage
37V
Output Current
5A
No. Of Pins
7
Operating Temperature Range
-40°C To +125°C
Msl
MSL 3 - 168 Hours
Supply Voltage Range
8V To 40V
Rohs Compliant
Yes
Filter Terminals
SMD
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Power - Output
-
Other names
*LM2678S-ADJ
*LM2678S-ADJ/NOPB
LM2678S-ADJ
*LM2678S-ADJ/NOPB
LM2678S-ADJ
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
www.national.com
use to estimate the ON time of the switch during which energy
is stored in the inductor.
For this example E•T is found to be:
Using Figure 6, the intersection of 27V•μS horizontally and
the 3.5A vertical line (I
inductor, or L49, a 33μH inductor could be used. Either in-
ductor will be suitable, but for this example selecting the larger
inductance will result in lower ripple current.
From Table 1, L48 in a surface mount component is available
from Pulse Engineering with part number P0848.
Step 4: Use Table 6 to determine an output capacitor. With a
14.8V output the 12.5 to 15V row is used and with a 47μH
inductor there are three surface mount output capacitor solu-
tions. Table 2 provides the actual capacitor characteristics
based on the C Code number. Any of the following choices
can be used:
1 x 33μF/20V AVX TPS (code C6)
1 x 47μF/20V Sprague 594 (code C8)
1 x 47μF/20V Kemet T495 (code C8)
Important Note: When using the adjustable device in low
voltage applications (less than 3V output), if the nomograph,
load
max) indicates that L48 , a 47μH
14
Figure 6, selects an inductance of 22μH or less, Table 6 does
not provide an output capacitor solution. With these condi-
tions the number of output capacitors required for stable
operation becomes impractical. It is recommended to use ei-
ther a 33μH or 47μH inductor and the output capacitors from
Table 6.
Step 5: An input capacitor for this example will require at least
a 35V WV rating with an rms current rating of 1.75A (1/2 Iout
max). From Table 2 it can be seen that C12, a 33μF/35V ca-
pacitor from Sprague, has the highest voltage/current rating
of the surface mount components and that two of these ca-
pacitor in parallel will be adquate.
Step 6: From Table 5 a 5A or more Schottky diode must be
selected. For surface mount diodes with a margin of safety on
the voltage rating one of two diodes can be used:
MBRD1545CT
6TQ045S
Step 7: A 0.01μF capacitor will be used for Cboost.
LLP PACKAGE DEVICES
The LM2678 is offered in the 14 lead LLP surface mount
package to allow for a significantly decreased footprint with
equivalent power dissipation compared to the TO-263. For
details on mounting and soldering specifications, refer to Ap-
plication Note AN-1187.