LM2672M-ADJ/NOPB National Semiconductor, LM2672M-ADJ/NOPB Datasheet - Page 17

• Manufacturer Part Number: LM2672M-ADJ/NOPB
• Description: IC REG SIMPLE SWITCHER 8-SOIC
• Manufacturer: National Semiconductor
• Series: SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM2672M-ADJ/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.21 ~ 37 V
• Current - Output: 1A
• Frequency - Switching: 260kHz
• Voltage - Input: 6.5 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Primary Input Voltage: 40V
• No. Of Outputs: 1
• Output Voltage: 37V
• Output Current: 1.55A
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +125°C
• Msl: MSL 1 - Unlimited
• Filter Terminals: SMD
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: *LM2672M-ADJ; *LM2672M-ADJ/NOPB; LM2672M-ADJ

To simplify the buck regulator design procedure, National
Semiconductor is making available computer design software to be
used with the SIMPLE SWITCHER line of switching regulators.
LM267X Made Simple version 6.0 is available on Windows 3.1,
NT, or 95 operating systems.
Given:
1. Programming Output Voltage (Selecting R
in Figure 3)
Use the following formula to select the appropriate resistor values.
Select a value for R
values minimize noise pickup in the sensitive feedback pin. (For the
lowest temperature coefficient and the best stability with time, use
1% metal film resistors.)
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant E • T
(V • μs), from the following formula:
where V
V
B. Use the E • T value from the previous formula and match it with
the E • T number on the vertical axis of the Inductor Value Selection
Guide shown in Figure 7.
C. On the horizontal axis, select the maximum load current.
D. Identify the inductance region intersected by the E • T value and
the Maximum Load Current value. Each region is identified by an
inductance value and an inductor code (LXX).
E. Select an appropriate inductor from the four manufacturer's part
numbers listed in Figure 8. For information on the different types of
inductors, see the inductor selection in the fixed output voltage
design procedure.
3. Output Capacitor SeIection (C
A. Select an output capacitor from the capacitor code selection
guide in Figure 16. Using the inductance value found in the inductor
selection guide, step 1, locate the appropriate capacitor code
corresponding to the desired output voltage.
D
LM2672 Series Buck Regulator Design Procedure (Adjustable Output)
V
V
I
F = Switching Frequency (Fixed at a nominal 260 kHz).
LOAD
= diode forward voltage drop = 0.5V
OUT
IN
(max) = Maximum Input Voltage
PROCEDURE (Adjustable Output Voltage Version)
(max) = Maximum Load Current
= Regulated Output Voltage
SAT
=internal switch saturation voltage=0.25V and
1
between 240Ω and 1.5 kΩ. The lower resistor
where V
REF
OUT
= 1.21V
)
1
and R
2
, as shown
17
Given:
1. Programming Output Voltage (Selecting R
in Figure 3)
Select R
R
R
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant (E • T),
B. E • T = 21.6 (V • μs)
C. I
D. From the inductor value selection guide shown in Figure 7, the
inductance region intersected by the 21.6 (V • μs) horizontal line
and the 1A vertical line is 68 μH, and the inductor code is L30.
E. From the table in Figure 8, locate line L30, and select an inductor
part number from the list of manufacturers' part numbers.
3. Output Capacitor SeIection (C
A. Use the appropriate row of the capacitor code selection guide,
in Figure 16. For this example, use the 15–20V row. The capacitor
code corresponding to an inductance of 68 μH is C20.
2
2
V
V
I
F = Switching Frequency (Fixed at a nominal 260 kHz).
LOAD
= 1 kΩ (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.
= 15.4 kΩ.
OUT
IN
LOAD
(max) = 28V
(max) = 1A
EXAMPLE (Adjustable Output Voltage Version)
= 20V
1
(max) = 1A
to be 1 kΩ, 1%. Solve for R
OUT
2
)
.
1
and R
www.national.com
2
, as shown