LM2576TV-012G ON Semiconductor, LM2576TV-012G Datasheet - Page 17

IC REG SW 3A 12V STEPDWN TO220-5

LM2576TV-012G

Manufacturer Part Number
LM2576TV-012G
Description
IC REG SW 3A 12V STEPDWN TO220-5
Manufacturer
ON Semiconductor
Type
Step-Down (Buck)r
Datasheet

Specifications of LM2576TV-012G

Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
12V
Current - Output
3A
Frequency - Switching
52kHz
Voltage - Input
7 ~ 40 V
Operating Temperature
-40°C ~ 125°C
Mounting Type
Through Hole
Package / Case
TO-220-5 (Bent and Staggered Leads)
Output Voltage
12 V
Output Current
3 A
Input Voltage
4.75 V to 40 V
Switching Frequency
52 KHz
Operating Temperature Range
- 40 C to + 125 C
Mounting Style
Through Hole
Duty Cycle (max)
98 %
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Power - Output
-
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
same printed circuit board, open core magnetics can cause
interference between two or more of the regulator circuits,
especially at high currents due to mutual coupling. A toroid,
pot core or E−core (closed magnetic structure) should be
used in such applications.
Do Not Operate an Inductor Beyond its
Maximum Rated Current
cause the inductor to overheat because of the copper wire
losses, or the core may saturate. Core saturation occurs when
the flux density is too high and consequently the cross
sectional area of the core can no longer support additional
lines of magnetic flux.
inductance value decreases rapidly and the inductor begins
to look mainly resistive. It has only the DC resistance of the
winding. This can cause the switch current to rise very
rapidly and force the LM2576 internal switch into
cycle−by−cycle current limit, thus reducing the DC output
load current. This can also result in overheating of the
Output Voltage Ripple and Transients
Source of the Output Ripple
regulator, its output voltage, if left unfiltered, will contain a
sawtooth ripple voltage at the switching frequency. The
output ripple voltage value ranges from 0.5% to 3% of the
output voltage. It is caused mainly by the inductor sawtooth
ripple current multiplied by the ESR of the output capacitor.
Short Voltage Spikes and How to Reduce Them
voltage spikes at the peaks of the sawtooth waveform (see
Figure 25). These voltage spikes are present because of the
fast switching action of the output switch, and the parasitic
inductance of the output filter capacitor. There are some
other important factors such as wiring inductance, stray
capacitance, as well as the scope probe used to evaluate these
transients, all these contribute to the amplitude of these
spikes. To minimize these voltage spikes, low inductance
capacitors should be used, and their lead lengths must be
kept short. The importance of quality printed circuit board
layout design should also be highlighted.
Unfiltered
When multiple switching regulators are located on the
Exceeding an inductor’s maximum current rating may
This causes the permeability of the core to drop, the
Since the LM2576 is a switch mode power supply
The regulator output voltage may also contain short
Filtered
Voltage
Voltage
Output
Output
Figure 25. Output Ripple Voltage Waveforms
HORIZONTAL TIME BASE: 5.0 ms/DIV
GENERAL RECOMMENDATIONS
Voltage spikes
caused by
switching action
of the output
switch and the
parasitic
inductance of the
output capacitor
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LM2576
17
inductor and/or the LM2576. Different inductor types have
different saturation characteristics, and this should be kept
in mind when selecting an inductor.
Minimizing the Output Ripple
to enlarge the inductance value of the inductor L1 and/or to
use a larger value output capacitor. There is also another way
to smooth the output by means of an additional LC filter (20
mH, 100 mF), that can be added to the output (see Figure 34)
to further reduce the amount of output ripple and transients.
With such a filter it is possible to reduce the output ripple
voltage transients 10 times or more. Figure 25 shows the
difference between filtered and unfiltered output waveforms
of the regulator shown in Figure 34.
of the converter, while the upper waveform shows the output
ripple voltage filtered by an additional LC filter.
Heatsinking and Thermal Considerations
The Through−Hole Package TO−220
TO−220(T, TV) and a 5−pin surface mount D
Although the TO−220(T) package needs a heatsink under
most conditions, there are some applications that require no
heatsink to keep the LM2576 junction temperature within
the allowed operating range. Higher ambient temperatures
require some heat sinking, either to the printed circuit (PC)
board or an external heatsink.
The Surface Mount Package D
Heatsinking
designed to be soldered to the copper on the PC board. The
copper and the board are the heatsink for this package and
the other heat producing components, such as the catch
diode and inductor. The PC board copper area that the
package is soldered to should be at least 0.4 in
and ideally should have 2 or more square inches (1300 mm
of 0.0028 inch copper. Additional increases of copper area
Waveform
Waveform
Inductor
In order to minimize the output ripple voltage it is possible
The lower waveform is from the normal unfiltered output
The LM2576 is available in two packages, a 5−pin
The other type of package, the surface mount D
Current
Current
Figure 24. Discontinuous Mode Switching Current
Switch
Power
0.4 A
0.4 A
0 A
0 A
HORIZONTAL TIME BASE: 5.0 ms/DIV
Waveforms
2
PAK and its
2
(or 260 mm
2
PAK(D2T).
2
PAK, is
2
2
)
)

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