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LM2596TVADJG

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P25
LM2596
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13
Table 3. INDUCTOR MANUFACTURERS PART NUMBERS
Inductance
(mH)
Current
(A)
Schott Renco Pulse Engineering Coilcraft
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount
Through
Hole
Surface
Mount
Surface Mount
L15 22 0.99 67148350 67148460 RL−1284−22−43 RL1500−2
2
PE−53815 PE−53815−S DO3308−223
L21 68 0.99 67144070 67144450 RL−5471−5 RL1500−6
8
PE−53821 PE−53821−S DO3316−683
L22 47 1.17 67144080 67144460 RL−5471−6 − PE−53822 PE−53822−S DO3316−473
L23 33 1.40 67144090 67144470 RL−5471−7 − PE−53823 PE−53823−S DO3316−333
L24 22 1.70 67148370 67148480 RL−1283−22−43 − PE−53824 PE−53825−S DO3316−223
L25 15 2.10 67148380 67148490 RL−1283−15−43 − PE−53825 PE−53824−S DO3316−153
L26 330 0.80 67144100 67144480 RL−5471−1 − PE−53826 PE−53826−S DO5022P−334
L27 220 1.00 67144110 67144490 RL−5471−2 − PE−53827 PE−53827−S DO5022P−224
L28 150 1.20 67144120 67144500 RL−5471−3 − PE−53828 PE−53828−S DO5022P−154
L29 100 1.47 67144130 67144510 RL−5471−4 − PE−53829 PE−53829−S DO5022P−104
L30 68 1.78 67144140 67144520 RL−5471−5 − PE−53830 PE−53830−S DO5022P−683
L31 47 2.20 67144150 67144530 RL−5471−6 − PE−53831 PE−53831−S DO5022P−473
L32 33 2.50 67144160 67144540 RL−5471−7 − PE−53932 PE−53932−S DO5022P−333
L33 22 3.10 67148390 67148500 RL−1283−22−43 − PE−53933 PE−53933−S DO5022P−223
L34 15 3.40 67148400 67148790 RL−1283−15−43 − PE−53934 PE−53934−S DO5022P−153
L35 220 1.70 67144170 − RL−5473−1 − PE−53935 PE−53935−S −
L36 150 2.10 67144180 − RL−5473−4 − PE−54036 PE−54036−S −
L37 100 2.50 67144190 − RL−5472−1 − PE−54037 PE−54037−S −
L38 68 3.10 67144200 − RL−5472−2 − PE−54038 PE−54038−S DO5040H−683ML
L39 47 3.50 67144210 − RL−5472−3 − PE−54039 PE−54039−S DO5040H−473ML
L40 33 3.50 67144220 67148290 RL−5472−4 − PE−54040 PE−54040−S DO5040H−333ML
L41 22 3.50 67144230 67148300 RL−5472−5 − PE−54041 PE−54041−S DO5040H−223ML
L42 150 2.70 67148410 − RL−5473−4 − PE−54042 PE−54042−S −
L43 100 3.40 67144240 − RL−5473−2 − PE−54043
-
L44 68 3.40 67144250 − RL−5473−3 − PE−54044 DO5040H−683ML
LM2596
http://onsemi.com
14
APPLICATION INFORMATION
EXTERNAL COMPONENTS
Input Capacitor (C
in
)
The Input Capacitor Should Have a Low ESR
For stable operation of the switch mode converter a low
ESR (Equivalent Series Resistance) aluminium or solid
tantalum bypass capacitor is needed between the input pin
and the ground pin, to prevent large voltage transients from
appearing at the input. It must be located near the regulator
and use short leads. With most electrolytic capacitors, the
capacitance value decreases and the ESR increases with
lower temperatures. For reliable operation in temperatures
below −25°C larger values of the input capacitor may be
needed. Also paralleling a ceramic or solid tantalum
capacitor will increase the regulator stability at cold
temperatures.
RMS Current Rating of C
in
The important parameter of the input capacitor is the RMS
current rating. Capacitors that are physically large and have
large surface area will typically have higher RMS current
ratings. For a given capacitor value, a higher voltage
electrolytic capacitor will be physically larger than a lower
voltage capacitor, and thus be able to dissipate more heat to
the surrounding air, and therefore will have a higher RMS
current rating. The consequence of operating an electrolytic
capacitor beyond the RMS current rating is a shortened
operating life. In order to assure maximum capacitor
operating lifetime, the capacitor’s RMS ripple current rating
should be:
I
rms
> 1.2 x d x I
Load
where d is the duty cycle, for a buck regulator
d +
t
on
T
+
V
out
V
in
and d +
t
on
T
+
|V
out
|
|V
out
| ) V
in
for a buck*boost regulator.
Output Capacitor (C
out
)
For low output ripple voltage and good stability, low ESR
output capacitors are recommended. An output capacitor
has two main functions: it filters the output and provides
regulator loop stability. The ESR of the output capacitor and
the peak−to−peak value of the inductor ripple current are the
main factors contributing to the output ripple voltage value.
Standard aluminium electrolytics could be adequate for
some applications but for quality design, low ESR types are
recommended.
An aluminium electrolytic capacitor’s ESR value is
related to many factors such as the capacitance value, the
voltage rating, the physical size and the type of construction.
In most cases, the higher voltage electrolytic capacitors have
lower ESR value. Often capacitors with much higher
voltage ratings may be needed to provide low ESR values
that, are required for low output ripple voltage.
Feedfoward Capacitor
(Adjustable Output Voltage Version)
This capacitor adds lead compensation to the feedback
loop and increases the phase margin for better loop stability.
For C
FF selection, see the design procedure section.
The Output Capacitor Requires an ESR Value
That Has an Upper and Lower Limit
As mentioned above, a low ESR value is needed for low
output ripple voltage, typically 1% to 2% of the output
voltage. But if the selected capacitor’s ESR is extremely low
(below 0.05 W), there is a possibility of an unstable feedback
loop, resulting in oscillation at the output. This situation can
occur when a tantalum capacitor, that can have a very low
ESR, is used as the only output capacitor.
At Low Temperatures, Put in Parallel Aluminium
Electrolytic Capacitors with Tantalum Capacitors
Electrolytic capacitors are not recommended for
temperatures below −25°C. The ESR rises dramatically at
cold temperatures and typically rises 3 times at −25°C and
as much as 10 times at −40°C. Solid tantalum capacitors
have much better ESR spec at cold temperatures and are
recommended for temperatures below −25°C. They can be
also used in parallel with aluminium electrolytics. The value
of the tantalum capacitor should be about 10% or 20% of the
total capacitance. The output capacitor should have at least
50% higher RMS ripple current rating at 150 kHz than the
peak−to−peak inductor ripple current.
LM2596
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15
Catch Diode
Locate the Catch Diode Close to the LM2596
The LM2596 is a step−down buck converter; it requires a
fast diode to provide a return path for the inductor current
when the switch turns off. This diode must be located close
to the LM2596 using short leads and short printed circuit
traces to avoid EMI problems.
Use a Schottky or a Soft Switching
Ultra−Fast Recovery Diode
Since the rectifier diodes are very significant sources of
losses within switching power supplies, choosing the
rectifier that best fits into the converter design is an
important process. Schottky diodes provide the best
performance because of their fast switching speed and low
forward voltage drop.
They provide the best efficiency especially in low output
voltage applications (5.0 V and lower). Another choice
could be Fast−Recovery, or Ultra−Fast Recovery diodes. It
has to be noted, that some types of these diodes with an
abrupt turnoff characteristic may cause instability or
EMI troubles.
A fast−recovery diode with soft recovery characteristics
can better fulfill some quality, low noise design requirements.
Table 2 provides a list of suitable diodes for the LM2596
regulator. Standard 50/60 Hz rectifier diodes, such as the
1N4001 series or 1N5400 series are NOT suitable.
Inductor
The magnetic components are the cornerstone of all
switching power supply designs. The style of the core and
the winding technique used in the magnetic component’s
design has a great influence on the reliability of the overall
power supply.
Using an improper or poorly designed inductor can cause
high voltage spikes generated by the rate of transitions in
current within the switching power supply, and the
possibility of core saturation can arise during an abnormal
operational mode. Voltage spikes can cause the
semiconductors to enter avalanche breakdown and the part
can instantly fail if enough energy is applied. It can also
cause significant RFI (Radio Frequency Interference) and
EMI (Electro−Magnetic Interference) problems.
Continuous and Discontinuous Mode of Operation
The LM2596 step−down converter can operate in both the
continuous and the discontinuous modes of operation. The
regulator works in the continuous mode when loads are
relatively heavy, the current flows through the inductor
continuously and never falls to zero. Under light load
conditions, the circuit will be forced to the discontinuous
mode when inductor current falls to zero for certain period
of time (see Figure 19 and Figure 20). Each mode has
distinctively different operating characteristics, which can
affect the regulator performance and requirements. In many
cases the preferred mode of operation is the continuous
mode. It offers greater output power, lower peak currents in
the switch, inductor and diode, and can have a lower output
ripple voltage. On the other hand it does require larger
inductor values to keep the inductor current flowing
continuously, especially at low output load currents and/or
high input voltages.
To simplify the inductor selection process, an inductor
selection guide for the LM2596 regulator was added to this
data sheet (Figure 18). This guide assumes that the regulator
is operating in the continuous mode, and selects an inductor
that will allow a peak−to−peak inductor ripple current to be
a certain percentage of the maximum design load current.
This percentage is allowed to change as different design load
currents are selected. For light loads (less than
approximately 300 mA) it may be desirable to operate the
regulator in the discontinuous mode, because the inductor
value and size can be kept relatively low. Consequently, the
percentage of inductor peak−to−peak current increases. This
discontinuous mode of operation is perfectly acceptable for
this type of switching converter. Any buck regulator will be
forced to enter discontinuous mode if the load current is light
enough.
HORIZONTAL TIME BASE: 2.0 ms/DIV
Figure 19. Continuous Mode Switching Current
Waveforms
VERTRICAL RESOLUTION 1.0 A/DIV
2.0 A
0 A
2.0 A
0 A
Inductor
Current
Waveform
Power
Switch
Current
Waveform
Selecting the Right Inductor Style
Some important considerations when selecting a core type
are core material, cost, the output power of the power supply,
the physical volume the inductor must fit within, and the
amount of EMI (Electro−Magnetic Interference) shielding
that the core must provide. The inductor selection guide
covers different styles of inductors, such as pot core, E−core,
toroid and bobbin core, as well as different core materials
such as ferrites and powdered iron from different
manufacturers.
For high quality design regulators the toroid core seems to
be the best choice. Since the magnetic flux is contained
within the core, it generates less EMI, reducing noise
problems in sensitive circuits. The least expensive is the
bobbin core type, which consists of wire wound on a ferrite
rod core. This type of inductor generates more EMI due to
the fact that its core is open, and the magnetic flux is not
contained within the core.
When multiple switching regulators are located on the
same printed circuit board, open core magnetics can cause
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LM2596TVADJG

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Manufacturer:
ON Semiconductor
Description:
Switching Voltage Regulators 3A BUCK SWCH 150KHZ
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