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參數(shù)資料
| 型號(hào)： | LM5000SD-6 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 16 Characters x 2 Lines, 5x7 Dot Matrix Character and Cursor |
| 中文描述： | 2.7 A SWITCHING REGULATOR, 1545 kHz SWITCHING FREQ-MAX, DSO16 |
| 封裝： | LLP-16 |
| 文件頁(yè)數(shù)： | 13/18頁(yè) |
| 文件大小： | 438K |
| 代理商： | LM5000SD-6 |
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Operation
(Continued)
where I
LOAD
is the maximum load current.
SELECTING THE COMPENSATION COMPONENTS
The first step in selecting the compensation components R
C
and C
C
is to set a dominant low frequency pole in the control
loop. Simply choose values for R
C
and C
C
within the ranges
given in the
Introduction to Compensation
section to set this
pole in the area of 10Hz to 100Hz. The frequency of the pole
created is determined by the equation:
where R
is the output impedance of the error amplifier,
850k
. Since R
is generally much less than R
, it does not
have much effect on the above equation and can be ne-
glected until a value is chosen to set the zero f
. f
is
created to cancel out the pole created by the output capaci-
tor, f
. The output capacitor pole will shift with different load
currents as shown by the equation, so setting the zero is not
exact. Determine the range of f
P1
over the expected loads
and then set the zero f
ZC
to a point approximately in the
middle. The frequency of this zero is determined by:
Now R
can be chosen with the selected value for C
C
.
Check to make sure that the pole f
is still in the 10Hz to
100Hz range, change each value slightly if needed to ensure
both component values are in the recommended range.After
checking the design at the end of this section, these values
can be changed a little more to optimize performance if
desired. This is best done in the lab on a bench, checking the
load step response with different values until the ringing and
overshoot on the output voltage at the edge of the load steps
is minimal. This should produce a stable, high performance
circuit. For improved transient response, higher values of R
C
(within the range of values) should be chosen. This will
improve the overall bandwidth which makes the regulator
respond more quickly to transients. If more detail is required,
or the most optimal performance is desired, refer to a more
in depth discussion of compensating current mode DC/DC
switching regulators.
HIGH OUTPUT CAPACITOR ESR COMPENSATION
When using an output capacitor with a high ESR value, or
just to improve the overall phase margin of the control loop,
another pole may be introduced to cancel the zero created
by the ESR. This is accomplished by adding another capaci-
tor, C
, directly from the compensation pin V
to ground, in
parallel with the series combination of R
and C
C
. The pole
should be placed at the same frequency as f
Z1
, the ESR
zero. The equation for this pole follows:
To ensure this equation is valid, and that C
C2
can be used
without negatively impacting the effects of R
C
and C
C
, f
PC2
must be greater than 10f
PC
.
CHECKING THE DESIGN
The final step is to check the design. This is to ensure a
bandwidth of
1
2
or less of the frequency of the RHP zero.
This is done by calculating the open-loop DC gain,A
DC
.After
this value is known, you can calculate the crossover visually
by placing a 20dB/decade slope at each pole, and a +20dB/
decade slope for each zero. The point at which the gain plot
crosses unity gain, or 0dB, is the crossover frequency. If the
crossover frequency is at less than
1
2
the RHP zero, the
phase margin should be high enough for stability. The phase
margin can also be improved some by adding C
C2
as dis-
cussed earlier in the section. The equation for A
is given
below with additional equations required for the calculation:
mc
)
0.072fs (in A/s)
where R
L
is the minimum load resistance, V
IN
is the maxi-
mum input voltage, and R
DSON
is the value chosen from the
graph "R
DSON
vs. V
IN
" in the
Typical Performance Charac-
teristics
section.
SWITCH VOLTAGE LIMITS
In a flyback regulator, the maximum steady-state voltage
appearing at the switch, when it is off, is set by the trans-
former turns ratio, N, the output voltage, V
OUT
, and the
maximum input voltage, V
IN
(Max):
V
SW(OFF)
= V
IN
(Max) + (V
OUT
+V
F
)/N
where V
is the forward biased voltage of the output diode,
and is typically 0.5V for Schottky diodes and 0.8V for ultra-
fast recovery diodes. In certain circuits, there exists a volt-
age spike, V
, superimposed on top of the steady-state
voltage . Usually, this voltage spike is caused by the trans-
former leakage inductance and/or the output rectifier recov-
ery time. To “clamp” the voltage at the switch from exceeding
its maximum value, a transient suppressor in series with a
diode is inserted across the transformer primary.
If poor circuit layout techniques are used, negative voltage
transients may appear on the Switch pin. Applying a nega-
tive voltage (with respect to the IC’s ground) to any mono-
lithic IC pin causes erratic and unpredictable operation of
that IC. This holds true for the LM5000EP IC as well. When
used in a flyback regulator, the voltage at the Switch pin can
go negative when the switch turns on. The “ringing” voltage
L
www.national.com
13
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| LM5000SDX-6EP | High Voltage Switch Mode Regulator |
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| LM5000-3MTC | High Voltage Switch Mode Regulator |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM5000SD-6/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM5000SD-6EP | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Voltage Switch Mode Regulator |
| LM5000SDX-3 | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM5000SDX-3/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM5000SDX-3EP | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:High Voltage Switch Mode Regulator |
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