LM2574HVMX-3.3 National Semiconductor, LM2574HVMX-3.3 Datasheet - Page 14

• Manufacturer Part Number: LM2574HVMX-3.3
• Description: Conv DC-DC Single Inv/Step Down 4V to 60V 14-Pin SOIC W T/R
• Manufacturer: National Semiconductor
• Type: Inverting|Step Downr

Specifications of LM2574HVMX-3.3

• Package: 14SOIC W
• Number Of Outputs: 1
• Minimum Input Voltage: 4 V
• Maximum Input Voltage: 60 V
• Switching Frequency: 58 KHz
• Operating Supply Voltage: 60(Max) V
• Maximum Output Current: 0.5 A
• Output Type: Fixed
• Output Voltage: 3.3 V
• Switching Regulator: Yes
• Efficiency: 72(Typ) %
• Operating Temperature: -40 to 125 °C

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