LM2599SX-12/NOPB National Semiconductor, LM2599SX-12/NOPB Datasheet - Page 13

• Manufacturer Part Number: LM2599SX-12/NOPB
• Description: IC REG SW 12V 3A STP DN TO-263-7
• Manufacturer: National Semiconductor
• Series: SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM2599SX-12/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 12V
• Current - Output: 3A
• Frequency - Switching: 150kHz
• Voltage - Input: 4.5 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: D²Pak, TO-263 (7 leads + tab)
• For Use With: 551011367-021 - BOARD WEBENCH BUILD IT LM2599
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: *LM2599SX-12; *LM2599SX-12/NOPB; LM2599SX-12

LM2599 Series Buck Regulator Design Procedure (Adjustable Output)
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 manufactur-
er’s part numbers listed in Figure 8 .
3. Output Capacitor Selection (C
A. In the majority of applications, low ESR electrolytic or solid
tantalum capacitors between 82 µF and 820 µF provide the
best results. This capacitor should be located close to the IC
using short capacitor leads and short copper traces. Do not
use capacitors larger than 820 µF. For additional informa-
tion, see section on output capacitors in application
information section.
B. To simplify the capacitor selection procedure, refer to the
quick design table shown in Figure 3 . This table contains
different output voltages, and lists various output capacitors
that will provide the best design solutions.
C. The capacitor voltage rating should be at least 1.5 times
greater than the output voltage, and often much higher volt-
age ratings are needed to satisfy the low ESR requirements
needed for low output ripple voltage.
4. Feedforward Capacitor (C
For output voltages greater than approximately 10V, an ad-
ditional capacitor is required. The compensation capacitor is
typically between 100 pF and 33 nF, and is wired in parallel
with the output voltage setting resistor, R
tional stability for high output voltages, low input-output volt-
ages, and/or very low ESR output capacitors, such as solid
tantalum capacitors.
This capacitor type can be ceramic, plastic, silver mica, etc.
(Because of the unstable characteristics of ceramic capaci-
tors made with Z5U material, they are not recommended.)
(Continued)
D
PROCEDURE (Adjustable Output Voltage Version)
= diode forward voltage drop = 0.5V
SAT
= internal switch saturation voltage = 1.16V and
FF
) (See Figure 1 )
OUT
)
2
. It provides addi-
13
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
numbers.
3. Output Capacitor SeIection (C
A. See section on C
B. From the quick design table shown in Figure 3 , locate the
output voltage column. From that column, locate the output
voltage closest to the output voltage in your application. In
this example, select the 24V line. Under the output capacitor
section, select a capacitor from the list of through hole elec-
trolytic or surface mount tantalum types from four different
capacitor manufacturers. It is recommended that both the
manufacturers and the manufacturers series that are listed in
the table be used.
In this example, through hole aluminum electrolytic capaci-
tors from several different manufacturers are available.
C. For a 20V output, a capacitor rating of at least 30V or
more is needed. In this example, either a 35V or 50V capaci-
tor would work. A 50V rating was chosen because it has a
lower ESR which provides a lower output ripple voltage.
Other manufacturers or other types of capacitors may also
be used, provided the capacitor specifications (especially the
100 kHz ESR) closely match the types listed in the table.
Refer to the capacitor manufacturers data sheet for this
information.
4. Feedforward Capacitor (C
The table shown in Figure 3 contains feed forward capacitor
values for various output voltages. In this example, a 560 pF
capacitor is needed.
LOAD
220/35 Panasonic HFQ Series
150/35 Nichicon PL Series
EXAMPLE (Adjustable Output Voltage Version)
(max) = 3A
OUT
in Application Information section.
FF
)
OUT
)
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