lm2577sx-adj National Semiconductor Corporation, lm2577sx-adj Datasheet - Page 16

• Manufacturer Part Number: lm2577sx-adj
• Description: Simple Switcher Step-up Voltage Regulator
• Manufacturer: National Semiconductor Corporation

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Application Hints
where V
recovery diodes (typically);
E • T, the product of volts x time that charges the inductor:
I
B. Identify Inductor Value:
If L
on to step C. Otherwise, the inductor value found in step B1
is too low; an appropriate inductor code should be obtained
from the graph as follows:
IND,DC
ditions for which the LM1577/LM2577 output switch
would be operating beyond its switch current rating. The
minimum operating voltage for the LM1577/LM2577 is
3.5V.
From here, proceed to step C.
2. For Adjustable version
Preliminary calculations:
The inductor selection is based on the calculation of the
following three parameters:
D
MIN
1. From Figure 9, identify the inductor code for the
region indicated by the intersection of E • T and I
This code gives the inductor value in microhenries. The
L or H prefix signifies whether the inductor is rated for a
maximum E • T of 90 V • µs (L) or 250 V • µs (H).
2. If D
the minimum inductance needed to ensure the switching
regulator’s stability:
(max)
, the average inductor current under full load;
is smaller than the inductor value found in step B1, go
F
, the maximum switch duty cycle (0 ≤ D ≤ 0.9):
<
= 0.5V for Schottky diodes and 0.8V for fast
0.85, go on to step C. If D ≥ 0.85, then calculate
(Continued)
IND,DC
.
16
1. Find the lowest value inductor that is greater than L
2. Find where E • T intersects this inductor value to determine
if it has an L or H prefix. If E • T intersects both the L and H
regions, select the inductor with an H prefix.
FIGURE 7. LM2577-12 Inductor Selection Guide
FIGURE 8. LM2577-15 Inductor Selection Guide
01146828
01146827
MIN
.