LM2575T-12 National Semiconductor, LM2575T-12 Datasheet - Page 15

• Manufacturer Part Number: LM2575T-12
• Description: Voltage Regulator IC
• Manufacturer: National Semiconductor

Specifications of LM2575T-12

• No. Of Pins: 5
• Output Current: 1A
• Peak Reflow Compatible (260 C): No
• Output Voltage: 12V
• Termination Type: Through Hole
• Supply Voltage Max: 40V
• Leaded Process Compatible: No
• Mounting Type: Through Hole
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Inductor Value Selection Guides
Given: V
Maximum Input Voltage I
Current F = Switching Frequency (Fixed at 52 kHz)
ficient and stability with time, use 1% metal film resistors)
it with the E • T number on the vertical axis of the Inductor
Value Selection Guide shown in Figure 7. C. On the hori-
zontal 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 code for
that region. E. Identify the inductor value from the inductor
code, and select an appropriate inductor from the table shown
in Figure 9. Part numbers are listed for three inductor manu-
facturers. The inductor chosen must be rated for operation at
the LM2575 switching frequency (52 kHz) and for a current
rating of 1.15 x I
the inductor section in the application hints section of this data
sheet.
and 2000 µF that will satisfy the loop requirements for stable
operation. But to achieve an acceptable output ripple voltage,
(approximately 1% of the output voltage) and transient re-
sponse, the output capacitor may need to be several times
larger than the above formula yields. B. The capacitor’s volt-
age rating should be at last 1.5 times greater than the output
voltage. For a 10V regulator, a rating of at least 15V or more
is recommended. Higher voltage electrolytic capacitors gen-
erally have lower ESR numbers, and for this reason it may be
necessary to select a capacitor rate for a higher voltage than
would normally be needed.
1. Programming Output Voltage (Selecting R1 and R2, as
rating must be at least 1.2 times greater than the maximum
3. Output Capacitor Selection (C
withstand a continuous output short, the diode should have
2. Inductor Selection (L1) A. Calculate the inductor Volt •
4. Catch Diode Selection (D1) A. The catch-diode current
Figure 8. B. The reverse voltage rating of the diode should
shown in Figure 2 ) Use the following formula to select the
R
B. Use the E • T value from the previous formula and match
The above formula yields capacitor values between 10 µF
a current rating equal to the maximum current limit of the
LM2575. The most stressful condition for this diode is an
microsecond constant, E • T (V • µs), from the following
stable operation, the capacitor must satisfy the following
overload or shorted output. See diode selection guide in
PROCEDURE (Adjustable Output Voltage Versions)
1
dominate pole-pair of the switching regulator loop. For
output capacitor together with the inductor defines the
can be between 1k and 5k. (For best temperature coef-
load current. Also, if the power supply design must
be at least 1.25 times the maximum input voltage.
OUT
= Regulated Output Voltage V
LOAD
appropriate resistor values.
. For additional inductor information, see
requirement:
LOAD
formula:
(Max) = Maximum Load
OUT
) A. The value of the
IN
(Max) =
(For Continuous Mode Operation) (Continued)
15
Given: V
52 kHz
1.Programming Output Voltage (Selecting R1 and R2)
2. Inductor Selection (L1) A. Calculate E • T (V • µs)
Region = H470 E. Inductor Value = 470 µH Choose from AIE
part #430-0634, Pulse Engineering part #PE-53118, or
Renco part #RL-1961.
3. Output Capacitor Selection (C
220 µF C
4. Catch Diode Selection (D1) A. For this example, a 3A
current rating is adequate. B. Use a 40V MBR340 or
31DQ04 Schottky diode, or any of the suggested
fast-recovery diodes in Figure 8.
However, for acceptable output ripple voltage select C
R2 = 1k (8.13 − 1) = 7.13k, closest 1% value is 7.15k
B. E • T = 115 V • µs C. I
EXAMPLE (Adjustable Output Voltage Versions)
OUT
OUT
= 10V V
= 220 µF electrolytic capacitor
IN
(Max) = 25V I
LOAD
(Max) = 1A D. Inductance
OUT
LOAD
) A.
(Max) = 1A F =
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OUT
≥