OMO ElectronicOMO Electronic
Expand menu
Hello, Sign inMy Account
0 Cart

LM2596DSADJG

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P25
LM2596
http://onsemi.com
16
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
Exceeding an inductor’s maximum current rating may
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.
This causes the permeability of the core to drop, the
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 LM2596 internal switch into
cycle−by−cycle current limit, thus reducing the DC output
load current. This can also result in overheating of the
inductor and/or the LM2596. Different inductor types have
different saturation characteristics, and this should be kept
in mind when selecting an inductor.
0.4 A
0 A
0.4 A
0 A
Inductor
Current
Waveform
Power
Switch
Current
Waveform
Figure 20. Discontinuous Mode Switching Current
Waveforms
VERTICAL RESOLUTION 200 mA/DIV
HORIZONTAL TIME BASE: 2.0 ms/DIV
GENERAL RECOMMENDATIONS
Output Voltage Ripple and Transients
Source of the Output Ripple
Since the LM2596 is a switch mode power supply
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
The regulator output voltage may also contain short
voltage spikes at the peaks of the sawtooth waveform (see
Figure 21). 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
Output
Voltage
Filtered
Output
Voltage
HORIZONTAL TIME BASE: 5.0 ms/DIV
Figure 21. Output Ripple Voltage Waveforms
VERTRICAL
Voltage spikes
caused by
switching action
of the output
switch and the
parasitic
inductance of the
output capacitor
RESOLUTION
20 mV/DIV
Minimizing the Output Ripple
In order to minimize the output ripple voltage it is possible
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 30)
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 21 shows the
difference between filtered and unfiltered output waveforms
of the regulator shown in Figure 30.
The lower waveform is from the normal unfiltered output
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
The LM2596 is available in two packages, a 5−pin
TO−220(T, TV) and a 5−pin surface mount D
2
PAK(D2T).
Although the TO−220(T) package needs a heatsink under
most conditions, there are some applications that require no
heatsink to keep the LM2596 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
2
PAK and its
Heatsinking
The other type of package, the surface mount D
2
PAK, is
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
2
(or 260 mm
2
)
and ideally should have 2 or more square inches (1300 mm
2
)
of 0.0028 inch copper. Additional increases of copper area
beyond approximately 6.0 in
2
(4000 mm
2
) will not improve
LM2596
http://onsemi.com
17
heat dissipation significantly. If further thermal
improvements are needed, double sided or multilayer PC
boards with large copper areas should be considered. In
order to achieve the best thermal performance, it is highly
recommended to use wide copper traces as well as large
areas of copper in the printed circuit board layout. The only
exception to this is the OUTPUT (switch) pin, which should
not have large areas of copper (see page 8 ‘PCB Layout
Guideline’).
Thermal Analysis and Design
The following procedure must be performed to determine
whether or not a heatsink will be required. First determine:
1. P
D(max)
maximum regulator power dissipation in the
application.
2. T
A(max
) maximum ambient temperature in the
application.
3. T
J(max)
maximum allowed junction temperature
(125°C for the LM2596). For a conservative
design, the maximum junction temperature
should not exceed 110°C to assure safe
operation. For every additional +10°C
temperature rise that the junction must
withstand, the estimated operating lifetime
of the component is halved.
4. R
q
JC
package thermal resistance junction−case.
5. R
q
JA
package thermal resistance junction−ambient.
(Refer to Maximum Ratings on page 2 of this data sheet or
R
q
JC
and R
q
JA
values).
The following formula is to calculate the approximate
total power dissipated by the LM2596:
P
D
= (V
in
x I
Q
) + d x I
Load
x V
sat
where d is the duty cycle and for buck converter
d +
t
on
T
+
V
O
V
in
,
I
Q
(quiescent current) and V
sat
can be found in the
LM2596 data sheet,
V
in
is minimum input voltage applied,
V
O
is the regulator output voltage,
I
Load
is the load current.
The dynamic switching losses during turn−on and
turn−off can be neglected if proper type catch diode is used.
Packages Not on a Heatsink (Free−Standing)
For a free−standing application when no heatsink is used,
the junction temperature can be determined by the following
expression:
T
J
= (R
q
JA
) (P
D
) + T
A
where (R
q
JA
)(P
D
) represents the junction temperature rise
caused by the dissipated power and T
A
is the maximum
ambient temperature.
Packages on a Heatsink
If the actual operating junction temperature is greater than
the selected safe operating junction temperature determined
in step 3, than a heatsink is required. The junction
temperature will be calculated as follows:
T
J
= P
D
(R
q
JA
+ R
q
CS
+ R
q
SA
) + T
A
where R
q
JC
is the thermal resistance junction−case,
R
q
CS
is the thermal resistance case−heatsink,
R
q
SA
is the thermal resistance heatsink−ambient.
If the actual operating temperature is greater than the
selected safe operating junction temperature, then a larger
heatsink is required.
Some Aspects That can Influence Thermal Design
It should be noted that the package thermal resistance and
the junction temperature rise numbers are all approximate,
and there are many factors that will affect these numbers,
such as PC board size, shape, thickness, physical position,
location, board temperature, as well as whether the
surrounding air is moving or still.
Other factors are trace width, total printed circuit copper
area, copper thickness, single− or double−sided, multilayer
board, the amount of solder on the board or even color of the
traces.
The size, quantity and spacing of other components on the
board can also influence its effectiveness to dissipate the heat.
Figure 22. Inverting Buck−Boost Develops −12 V
D1
1N5822
L1
33 mH
Feedback
12 to 40 V
Unregulated
DC Input
C
in
100 mF/50 V
GND
ON/OFF
+V
in
−12 V @ 0.7 A
Regulated
Output
C
out
220 mF
LM2596−ADJ
R3
R4
LM2596
http://onsemi.com
18
ADDITIONAL APPLICATIONS
Inverting Regulator
An inverting buck−boost regulator using the
LM2596−ADJ is shown in Figure 22. This circuit converts
a positive input voltage to a negative output voltage with a
common ground by bootstrapping the regulators ground to
the negative output voltage. By grounding the feedback pin,
the regulator senses the inverted output voltage and
regulates it.
In this example the LM2596−12 is used to generate a
−12 V output. The maximum input voltage in this case
cannot exceed +28 V because the maximum voltage
appearing across the regulator is the absolute sum of the
input and output voltages and this must be limited to a
maximum of 40 V.
This circuit configuration is able to deliver approximately
0.7 A to the output when the input voltage is 12 V or higher.
At lighter loads the minimum input voltage required drops
to approximately 4.7 V, because the buck−boost regulator
topology can produce an output voltage that, in its absolute
value, is either greater or less than the input voltage.
Since the switch currents in this buck−boost configuration
are higher than in the standard buck converter topology, the
available output current is lower.
This type of buck−boost inverting regulator can also
require a larger amount of startup input current, even for
light loads. This may overload an input power source with
a current limit less than 5.0 A.
Such an amount of input startup current is needed for at
least 2.0 ms or more. The actual time depends on the output
voltage and size of the output capacitor.
Because of the relatively high startup currents required by
this inverting regulator topology, the use of a delayed startup
or an undervoltage lockout circuit is recommended.
Using a delayed startup arrangement, the input capacitor
can charge up to a higher voltage before the switch−mode
regulator begins to operate.
The high input current needed for startup is now partially
supplied by the input capacitor C
in
.
It has been already mentioned above, that in some
situations, the delayed startup or the undervoltage lockout
features could be very useful. A delayed startup circuit
applied to a buck−boost converter is shown in Figure 27.
Figure 29 in the “Undervoltage Lockout” section describes
an undervoltage lockout feature for the same converter
topology.
Design Recommendations:
The inverting regulator operates in a different manner
than the buck converter and so a different design procedure
has to be used to select the inductor L1 or the output
capacitor C
out
.
The output capacitor values must be larger than what is
normally required for buck converter designs. Low input
voltages or high output currents require a large value output
capacitor (in the range of thousands of mF).
The recommended range of inductor values for the
inverting converter design is between 68 mH and 220 mH. To
select an inductor with an appropriate current rating, the
inductor peak current has to be calculated.
The following formula is used to obtain the peak inductor
current:
where t
on
+
|V
O
|
V
in
) |V
O
|
x
1.0
f
osc
, and f
osc
+ 52 kHz.
I
peak
[
I
Load
(V
in
) |V
O
|)
V
in
)
V
in
xt
on
2L
1
Under normal continuous inductor current operating
conditions, the worst case occurs when V
in
is minimal.
Figure 23. Inverting Buck−Boost Develops −12 V
D1
1N5822
L1
33 mH
Feedback
12 to 40 V
Unregulated
DC Input
C
in
100 mF/50 V
GND
ON/OFF
+V
in
−12 V @ 0.7 A
Regulated
Output
C
out
220 mF
LM2596−ADJ
R3
R4
C1
0.1 mF
R2
47k
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P25

LM2596DSADJG

Mfr. #:
Buy LM2596DSADJG
Manufacturer:
ON Semiconductor
Description:
Switching Voltage Regulators 3A BUCK SWCH 150KHZ
Lifecycle:
New from this manufacturer.
Delivery:
DHL FedEx Ups TNT EMS
Payment:
T/T Paypal Visa MoneyGram Western Union

Products related to this Datasheet