LM2596S-12 National Semiconductor, LM2596S-12 Datasheet - Page 12

• Manufacturer Part Number: LM2596S-12
• Description: DC/DC Converter IC
• Manufacturer: National Semiconductor

Specifications of LM2596S-12

• Input Voltage: 40V
• Output Current: 3A
• Output Voltage: 12V
• No. Of Pins: 5
• Termination Type: SMD
• Mounting Type: Through Hole
• Voltage Regulator Type: Buck Switching
• Output Current Max: 3A
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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LM2596 Series Buck Regulator Design Procedure (Adjustable Output)
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 • µs), from the following formula:
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
identified by an inductance value and an inductor code
(LXX).
E. Select an appropriate inductor from the four manufactur-
er’s part numbers listed in Figure 8 .
LOAD
OUT
IN
PROCEDURE (Adjustable Output Voltage Version)
(max) = Maximum Input Voltage
(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
12
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) horizon-
tal 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
and R
2
, as