LM3151_14 Datasheet, PDF (12/27 Pages) Texas Instruments – SIMPLE SWITCHER® CONTROLLER, High Input Voltage Synchronous Step-Down

LM3151, LM3152, LM3153
SNVS562G – SEPTEMBER 2008 – REVISED MARCH 2011
www.ti.com
Design Guide
The design guide provides the equations required to design with the LM3151/2/3 SIMPLE SWITCHER Controller.
WEBENCH design tool can be used with or in place of this section for a more complete and simplified design
process.
1. Define Power Supply Operating Conditions
a. Maximum and Minimum DC Input voltage
b. Maximum Expected Load Current during normal operation
c. Target Switching Frequency
2. Determine which IC Controller to Use
The desired input voltage range will determine which version of the LM3151/2/3 controller will be chosen. The
higher switching frequency options allow for physically smaller inductors but efficiency may decrease.
3. Determine Inductor Required Using Figure 13
To use the nomograph below calculate the inductor volt-microsecond constant ET from the following formula:
ET
=
(Vinmax
±
V_OUT)
x
V_OUT
Vinmax
x
1000
f_S
(V
x
Ps)
where
• f_S is in kHz units
The intersection of the Load Current and the Volt-microseconds lines on the chart below will determine which
inductors are capable for use in the design. The chart shows a sample of parts that can be used. The offline
calculator tools and WEBENCH will fully calculate the requirements for the components needed for the design.
100
90
80
70
60
50
40
30
20
10
9
8
7
6
5
4
3
2
1
4
L01
L02
L03
L04
L05
L06
L07
L08
L09
L10
L11
L12
5
47 ^PH
33 ^PH
L13
L25
L14
L26
L15
L27
L16
L28
L17
L29
L18
L30
L19
L31
L20
L32
L21
L33
L22
L34
L23
L35
L24
L36
6
7
8
9
10
MAXIMUM LOAD CURRENT (A)
L37 ^{22 PH}
L38 ^{15 PH}
L39 ^{10 PH}
L40 ^{6.8 PH}
L41 ^{4.7 PH}
L42 ^{3.3 PH}
L43 ^{2.2 PH}
L44 ^{1.5 PH}
L45 ^{1.0 PH}
L46 ^{0.68 PH}
L47 ^{0.47 PH}
L48 _0.33 PH
12
Figure 13. Inductor Nomograph
12
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