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参数资料
| 型号： | LM2595J-3.3-QML |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 2.6 A SWITCHING REGULATOR, 173 kHz SWITCHING FREQ-MAX, CDIP16 |
| 封装： | CERAMIC, DIP-16 |
| 文件页数： | 14/33页 |
| 文件大小： | 1016K |
| 代理商： | LM2595J-3.3-QML |
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Application Information (Continued)
eters such as, peak inductor or peak switch current, mini-
mum load current before the circuit becomes discontinuous,
output ripple voltage and output capacitor ESR can all be
calculated from the peak-to-peak
I
IND. When the inductor
nomographs shown in
Figure 4 through Figure 7 are used to
select an inductor value, the peak-to-peak inductor ripple
current can immediately be determined. The curve shown in
Figure 18 shows the range of (
I
IND) that can be expected
for different load currents. The curve also shows how the
peak-to-peak inductor ripple current (
I
IND) changes as you
go from the lower border to the upper border (for a given load
current) within an inductance region. The upper border rep-
resents a higher input voltage, while the lower border repre-
sents a lower input voltage (see Inductor Selection Guides).
These curves are only correct for continuous mode opera-
tion, and only if the inductor selection guides are used to se-
lect the inductor value
Consider the following example:
V
OUT = 5V, maximum load current of 800 mA
V
IN = 12V, nominal, varying between 10V and 14V.
The selection guide in
Figure 5 shows that the vertical line
for a 0.8A load current, and the horizontal line for the 12V in-
put voltage intersect approximately midway between the up-
per and lower borders of the 68 H inductance region. A 68
H inductor will allow a peak-to-peak inductor current (
I
IND)
to flow that will be a percentage of the maximum load cur-
rent. Referring to
Figure 18, follow the 0.8A line approxi-
mately midway into the inductance region, and read the
peak-to-peak inductor ripple current (
I
IND) on the left hand
axis (approximately 300 mA p-p).
As the input voltage increases to 14V, it approaches the up-
per border of the inductance region, and the inductor ripple
current increases. Referring to the curve in
Figure 18,itcan
be seen that for a load current of 0.8A, the peak-to-peak in-
ductor ripple current (
I
IND) is 300 mA with 12V in, and can
range from 340 mA at the upper border (14V in) to 225 mA at
the lower border (10V in).
Once the
I
IND value is known, the following formulas can be
used to calculate additional information about the switching
regulator circuit.
1.
Peak Inductor or peak switch current
2.
Minimum load current before the circuit becomes dis-
continuous
3.
Output Ripple Voltage = (
I
IND)x(ESR of COUT)
= 0.30Ax0.16
=48 mV p-p
4.
ESR of C
OUT
OPEN CORE INDUCTORS
Another possible source of increased output ripple voltage or
unstable operation is from an open core inductor. Ferrite
bobbin or stick inductors have magnetic lines of flux flowing
through the air from one end of the bobbin to the other end.
These magnetic lines of flux will induce a voltage into any
wire or PC board copper trace that comes within the induc-
tor’s magnetic field. The strength of the magnetic field, the
orientation and location of the PC copper trace to the mag-
netic field, and the distance between the copper trace and
the inductor, determine the amount of voltage generated in
the copper trace. Another way of looking at this inductive
coupling is to consider the PC board copper trace as one
turn of a transformer (secondary) with the inductor winding
as the primary. Many millivolts can be generated in a copper
trace located near an open core inductor which can cause
stability problems or high output ripple voltage problems.
If unstable operation is seen, and an open core inductor is
used, it’s possible that the location of the inductor with re-
spect to other PC traces may be the problem. To determine
if this is the problem, temporarily raise the inductor away
from the board by several inches and then check circuit op-
eration. If the circuit now operates correctly, then the mag-
netic flux from the open core inductor is causing the problem.
Substituting a closed core inductor such as a torroid or
E-core will correct the problem, or re-arranging the PC layout
may be necessary. Magnetic flux cutting the IC device
ground trace, feedback trace, or the positive or negative
traces of the output capacitor should be minimized.
Sometimes, locating a trace directly beneath a bobbin induc-
tor will provide good results, provided it is exactly in the cen-
ter of the inductor (because the induced voltages cancel
themselves out), but if it is off center one direction or the
other, then problems could arise. If flux problems are
present, even the direction of the inductor winding can make
a difference in some circuits.
This discussion on open core inductors is not to frighten the
user, but to alert the user on what kind of problems to watch
out for when using them. Open core bobbin or “stick” induc-
tors are an inexpensive, simple way of making a compact ef-
ficient inductor, and they are used by the millions in many dif-
ferent applications.
THERMAL CONSIDERATIONS
The LM2595 is available in two packages, a 5-pin TO-220
(T) and a 5-pin surface mount TO-263 (S).
The TO-220 package can be used without a heat sink for
ambient temperatures up to approximately 50C (depending
on the output voltage and load current). The curves in
Figure
19 show the LM2595T junction temperature rises above am-
bient temperature for different input and output voltages. The
data tor these curves was taken with the LM2595T (TO-220
package) operating as a switching regutator in an ambient
temperature of 25C (still air). These temperature rise num-
bers are all approximate and there are many factors that can
affect these temperatures. Higher ambient temperatures re-
quire some heat sinking, either to the PC board or a small
external heat sink.
The TO-263 surface mount package tab is designed to be
soldered to the copper on a printed circuit board. The copper
and the board are the heat sink 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, and ideally should
have 2 or more square inches of 2 oz. (0.0028 in) copper.
Additional copper area improves the thermal characteristics,
www.national.com
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相关PDF资料 |
PDF描述 |
|---|---|
| LM2595-5.0MDC | 2.6 A SWITCHING REGULATOR, 173 kHz SWITCHING FREQ-MAX, UUC |
| LM2595-5.0MWC | 2.6 A SWITCHING REGULATOR, 173 kHz SWITCHING FREQ-MAX, UUC |
| LM2595-3.3MDC | 2.6 A SWITCHING REGULATOR, 173 kHz SWITCHING FREQ-MAX, UUC |
| LM2595J-5.0-QML | 2.6 A SWITCHING REGULATOR, 173 kHz SWITCHING FREQ-MAX, CDIP16 |
| LM2599-5.0MWC | 7.5 A SWITCHING REGULATOR, 173 kHz SWITCHING FREQ-MAX, UUC |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LM2595S12 | 制造商:Texas Instruments 功能描述:SWITCHING REG, 1A 12V, SMD, 2595 制造商:Texas Instruments 功能描述:SWITCHING REG, 1A 12V, SMD, 2595; Primary Input Voltage:24V; No. of Outputs:1; Output Voltage:12V; Output Current:1A; Voltage Regulator Case Style:TO-263; No. of Pins:5; Operating Temperature Min:-25C; Operating Temperature ;RoHS Compliant: Yes |
| LM2595S-12 | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM2595S12 | 制造商:Texas Instruments 功能描述:IC SWITCHING REG 1A 12V SMD 2595 |
| LM2595S-12/NOPB | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| LM2595S-3.3 | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
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