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參數(shù)資料
| 型號： | LM3310 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Step-up PWM DC/DC Converter with Integrated Op-Amp and Gate Pulse Modulation Switch |
| 中文描述： | 升壓PWM直流/直流轉(zhuǎn)換器集成的運算放大器和脈沖調(diào)制開關(guān)門 |
| 文件頁數(shù)： | 17/25頁 |
| 文件大小： | 1668K |
| 代理商： | LM3310 |
Operation
(Continued)
The LM3310 is a current mode PWM boost converter. The
signal flow of this control scheme has two feedback loops,
one that senses switch current and one that senses output
voltage.
To keep a current programmed control converter stable
above duty cycles of 50%, the inductor must meet certain
criteria. The inductor, along with input and output voltage,
will determine the slope of the current through the inductor
(see
Figure 5
(a)). If the slope of the inductor current is too
great, the circuit will be unstable above duty cycles of 50%.
A 10μH inductor is recommended for most 660 kHz applica-
tions, while a 4.7μH inductor may be used for most 1.28 MHz
applications. If the duty cycle is approaching the maximum of
85%, it may be necessary to increase the inductance by as
much as 2X. See
Inductor and Diode Selection
for more
detailed inductor sizing.
The LM3310 provides a compensation pin (V
) to customize
the voltage loop feedback. It is recommended that a series
combination of R
and C
be used for the compensation
network, as shown in the typical application circuit. For any
given application, there exists a unique combination of R
C
and C
that will optimize the performance of the LM3310
circuit in terms of its transient response. The series combi-
nation of R
C
and C
C
introduces a pole-zero pair according to
the following equations:
where R
O
is the output impedance of the error amplifier,
approximately 900k
. For most applications, performance
can be optimized by choosing values within the range 5k
≤
R
C
≤
100k
(R
C
can be up to 200k
if C
C2
is used, see
High
Output Capacitor ESR Compensation
) and 68pF
≤
C
C
≤
4.7nF. Refer to the
Applications Information
section for rec-
ommended values for specific circuits and conditions. Refer
to the
Compensation
section for other design requirement.
COMPENSATION
This section will present a general design procedure to help
insure a stable and operational circuit. The designs in this
datasheet are optimized for particular requirements. If differ-
ent conversions are required, some of the components may
need to be changed to ensure stability. Below is a set of
general guidelines in designing a stable circuit for continu-
ous conduction operation, in most all cases this will provide
for stability during discontinuous operation as well. The
power components and their effects will be determined first,
then the compensation components will be chosen to pro-
duce stability.
INDUCTOR AND DIODE SELECTION
Although the inductor sizes mentioned earlier are fine for
most applications, a more exact value can be calculated. To
ensure stability at duty cycles above 50%, the inductor must
have some minimum value determined by the minimum
input voltage and the maximum output voltage. This equa-
tion is:
where fs is the switching frequency, D is the duty cycle, and
R
is the ON resistance of the internal switch taken from
the graph "R
vs. V
" in the
Typical Performance Char-
acteristics
section. This equation is only good for duty cycles
greater than 50% (D
>
0.5), for duty cycles less than 50% the
recommended values may be used. The value given by this
equation is the inductance necessary to supress sub-
harmonic oscillations. In some cases the value given by this
equation may be too small for a given application. In this
case the average inductor current and the inductor current
ripple must be considered.
The corresponding inductor current ripple, average inductor
current, and peak inductor current as shown in
Figure 5
(a) is
given by:
Continuous conduction mode occurs when
i
is less than
the average inductor current and discontinuous conduction
mode occurs when
i
is greater than the average inductor
current. Care must be taken to make sure that the switch will
not reach its current limit during normal operation. The in-
ductor must also be sized accordingly. It should have a
saturation current rating higher than the peak inductor cur-
rent expected. The output voltage ripple is also affected by
the total ripple current.
The output diode for a boost regulator must be chosen
correctly depending on the output voltage and the output
current. The typical current waveform for the diode in con-
tinuous conduction mode is shown in
Figure 5
(b). The diode
must be rated for a reverse voltage equal to or greater than
the output voltage used. The average current rating must be
greater than the maximum load current expected, and the
peak current rating must be greater than the peak inductor
current. During short circuit testing, or if short circuit condi-
tions are possible in the application, the diode current rating
must exceed the switch current limit. Using Schottky diodes
with lower forward voltage drop will decrease power dissipa-
tion and increase efficiency.
DC GAIN AND OPEN-LOOP GAIN
Since the control stage of the converter forms a complete
feedback loop with the power components, it forms a closed-
loop system that must be stabilized to avoid positive feed-
back and instability. A value for open-loop DC gain will be
required, from which you can calculate, or place, poles and
zeros to determine the crossover frequency and the phase
margin. A high phase margin (greater than 45) is desired for
the best stability and transient response. For the purpose of
stabilizing the LM3310, choosing a crossover point well be-
low where the right half plane zero is located will ensure
sufficient phase margin.
L
www.national.com
17
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| LM3310SQ | Step-up PWM DC/DC Converter with Integrated Op-Amp and Gate Pulse Modulation Switch |
| LM3310SQX | Step-up PWM DC/DC Converter with Integrated Op-Amp and Gate Pulse Modulation Switch |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3310_07 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Step-Up PWM DC/DC Converter with Integrated Op-Amp and Gate Pulse Modulation Switch |
| LM3310SQ | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM3310SQ/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM3310SQX | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| LM3310SQX/NOPB | 功能描述:DC/DC 開關(guān)控制器 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
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