LM2574HVN15

Manufacturer Part NumberLM2574HVN15
DescriptionDIP8
ManufacturerNational Semiconductor
LM2574HVN15 datasheet
 


Specifications of LM2574HVN15

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LM2574 Series Buck Regulator Design Procedure
FIGURE 8. LM2574HV-ADJ Inductor Selection Guide
PROCEDURE (Adjustable Output Voltage Versions)
Given:
= Regulated Output Voltage
V
OUT
(Max) = Maximum Input Voltage
V
IN
(Max) = Maximum Load Current
I
LOAD
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.
R
can be between 1k and 5k. (For best temperature coeffi-
1
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:
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 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 in-
ductor value for that region.
E. Select an appropriate inductor from the table shown in Fig-
ure 3 . Part numbers are listed for three inductor manufactur-
ers. 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
. For additional inductor information, see the in-
LOAD
ductor section in the application hints section of this data
sheet.
www.national.com
(Continued)
DS011394-16
EXAMPLE (Adjustable Output Voltage Versions)
Given:
= 24V
V
OUT
(Max) = 40V
V
IN
(Max) = 0.4A
I
LOAD
F = 52 kHz
1. Programming Output Voltage (Selecting R1 and R2)
= 1k (19.51−1) = 18.51k, closest 1% value is 18.7k
R
2
2. Inductor Selection (L1)
A. Calculate E • T (V • µs)
B. E • T = 185 V • µs
(Max) = 0.4A
C. I
LOAD
D. Inductance Region = 1000
E. Inductor Value = 1000 µH Choose from Pulse Engineer-
ing Part # PE-52631, or Renco Part # RL-1283-1000.
14