LM2574N-015G ON Semiconductor, LM2574N-015G Datasheet - Page 17

• Manufacturer Part Number: LM2574N-015G
• Description: IC REG SW 0.5A 15V OUTPUT 8-DIP
• Manufacturer: ON Semiconductor
• Type: Step-Down (Buck)r

Specifications of LM2574N-015G

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 15V
• Current - Output: 500mA
• Frequency - Switching: 52kHz
• Voltage - Input: 4.75 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Output Voltage: 15 V
• Output Current: 0.5 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

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 26). 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.
Waveform
Waveform
Inductor
Since the LM2574 is a switch mode power supply
The regulator output voltage may also contain short
Unfiltered
Current
Current
Switch
Power
Voltage
Filtered
Voltage
Output
Output
0.5 A
0.5 A
0 A
0 A
Figure 26. Output Ripple Voltage Waveforms
Voltage spikes caused by switching action of the output
switch and the parasitic inductance of the output capacitor
Figure 24. Continuous Mode Switching
HORIZONTAL TIME BASE: 5.0 ms/DIV
HORIZONTAL TIME BASE: 5.0 ms/DIV
Current Waveforms
GENERAL RECOMMENDATIONS
LM2574, NCV2574
http://onsemi.com
17
Waveform
Waveform
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 35) 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 26
shows the difference between filtered and unfiltered output
waveforms of the regulator shown in Figure 34.
of the converter, while the lower waveform shows the output
ripple voltage filtered by an additional LC filter.
Heatsinking and Thermal Considerations
packages. When used in the typical application the copper lead
frame conducts the majority of the heat from the die, through
the leads, to the printed circuit copper. The copper and the
board are the heatsink for this package and the other heat
producing components, such as the catch diode and inductor.
should be used and all ground and unused pins should be
soldered to generous amounts of printed circuit board
copper, such as a ground plane. Large areas of copper
provide the best transfer of heat to the surrounding air. One
exception to this is the output (switch) pin, which should not
have large areas of copper in order to minimize coupling to
sensitive circuitry.
achieved even by using of double sided or multilayer boards
which can provide even better heat path to the ambient.
Using a socket for the 8−pin DIP package is not
recommended because socket represents an additional
thermal resistance, and as a result the junction temperature
will be higher.
Inductor
Current
Current
Switch
In order to minimize the output ripple voltage it is possible
The upper waveform is from the normal unfiltered output
The LM2574 is available in both 8−pin DIP and SO−16L
For the best thermal performance, wide copper traces
Power
Additional improvement in heat dissipation can be
0.1 A
0.1 A
0 A
0 A
Figure 25. Discontinuous Mode Switching
HORIZONTAL TIME BASE: 5.0 ms/DIV
Current Waveforms