551011367-041 National Semiconductor, 551011367-041 Datasheet - Page 13

• Manufacturer Part Number: 551011367-041
• Description: BOARD WEBENCH BUILD IT
• Manufacturer: National Semiconductor
• Series: WEBENCH® Buildit Boardr

Specifications of 551011367-041

• Main Purpose: DC/DC, Step Down
• Regulator Topology: Buck
• Board Type: Bare (Unpopulated)
• Utilized Ic / Part: LM2596
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Current - Output: -
• Voltage - Output: -
• Voltage - Input: -
• Power - Output: -
• Frequency - Switching: -
• Outputs And Type: -
• Other names: *551011367-041

Given:
V
V
I
F = Switching Frequency (Fixed at a nominal 150 kHz).
1. Programming Output Voltage (Selecting R
shown in Figure 1 )
Use the following formula to select the appropriate resistor
values.
Select a value for R
resistor values minimize noise pickup in the sensitive feed-
back 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
where V
and 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 identi-
fied 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 .
• µs), from the following formula:
LM2596 Series Buck Regulator Design Procedure (Adjustable Output)
LOAD
OUT
IN
(max) = Maximum Input Voltage
PROCEDURE (Adjustable Output Voltage Version)
(max) = Maximum Load Current
D
= Regulated Output Voltage
= diode forward voltage drop = 0.5V
SAT
= internal switch saturation voltage = 1.16V
1
between 240
and 1.5 k . The lower
1
and R
2
, as
13
Given:
V
V
I
F = Switching Frequency (Fixed at a nominal 150 kHz).
1. Programming Output Voltage (Selecting R
shown in Figure 1 )
Select R
R
R
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant
(E • T),
B. E • T = 34.2 (V • µs)
C. I
D. From the inductor value selection guide shown in Figure 7 ,
the inductance region intersected by the 34 (V • µs) horizontal
line and the 3A vertical line is 47 µH, and the inductor code is
L39.
E. From the table in Figure 8 , locate line L39, and select an
inductor part number from the list of manufacturers part num-
bers.
LOAD
OUT
IN
2
2
(max) = 28V
= 1k (16.26 − 1) = 15.26k, closest 1% value is 15.4 k .
= 15.4 k .
LOAD
EXAMPLE (Adjustable Output Voltage Version)
(max) = 3A
= 20V
(max) = 3A
1
to be 1 k , 1%. Solve for R
2
.
1
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and R
2
, as