LM2574M-12 National Semiconductor, LM2574M-12 Datasheet - Page 16

• Manufacturer Part Number: LM2574M-12
• Description: IC,SMPS CONTROLLER,VOLTAGE-MODE,BIPOLAR,SOP,14PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LM2574M-12

• Rohs Compliant: NO

Given: V
Maximum Input Voltage I
F = Switching Frequency (Fixed at 52 kHz)
1. Programming Output Voltage (Selecting R1 and R2, as
shown in Figure 2) Use the following formula to select the
appropriate resistor values.
cient and 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:
it with the E • T number on the vertical axis of the Inductor
Value Selection Guide shown in Figure 8.
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, and note the inductor
value for that region.
E. Select an appropriate inductor from the table shown in
Figure 3. Part numbers are listed for three inductor manufac-
turers. The inductor chosen must be rated for operation at the
LM2574 switching frequency (52 kHz) and for a current rating
of 1.5 x I
inductor section in the application hints section of this data
sheet.
LM2574 Series Buck Regulator Design Procedure
R
B. Use the E • T value from the previous formula and match
1
PROCEDURE (Adjustable Output Voltage Versions)
can be between 1k and 5k. (For best temperature coeffi-
OUT
LOAD
= Regulated Output Voltage V
. For additional inductor information, see the
LOAD
(Max) = Maximum Load Current
FIGURE 8. LM2574HV-ADJ Inductor Selection Guide
IN
(Max) =
15
Given: V
52 kHz
1. Programming Output Voltage (Selecting R1 and R2)
2. Inductor Selection (L1)
A. Calculate E • T (V • µs)
C. I
D. Inductance Region = 1000
E. Inductor Value = 1000 µH Choose fromPulse Engineering
Part #PE-52631, or Renco Part #RL-1283-1000.
R
B. E • T = 185 V • µs
2
LOAD
= 1k (19.51−1) = 18.51k, closest 1% value is 18.7k
EXAMPLE (Adjustable Output Voltage Versions)
(Max) = 0.4A
OUT
= 24V V
01139416
(Continued)
IN
(Max) = 40V I
LOAD
(Max) = 0.4A F =
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