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參數(shù)資料
| 型號(hào)： | LM2715 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | TFT Panel Module |
| 中文描述： | 液晶面板模塊 |
| 文件頁(yè)數(shù)： | 15/20頁(yè) |
| 文件大?。?/td> | 746K |
| 代理商： | LM2715 |
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Operation
(Continued)
INTRODUCTION TO COMPENSATION
The LM2715 contains 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 2
(a)). If the slope of the inductor current is too
great, the circuit will be unstable above duty cycles of 50%.
A 4.7μH inductor is recommended for most 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 LM2715 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 LM2715
circuit in terms of its transient response. The series combi-
nation of R
and C
introduces a pole-zero pair according to
the following equations:
where R
is the output impedance of the error amplifier,
approximately 1M
. For most applications, performance can
be optimized by choosing values within the range 5k
≤
R
C
≤
40k
(R
can be up to 200k
if C
is used, see
High
Output Capacitor ESR Compensation
) and 680pF
≤
C
C
≤
4.7nF. Refer to the Typical Application Circuit and the
Appli-
cations Information
section for recommended values for spe-
cific circuits and conditions. Refer to the
Compensation
sec-
tion for other design requirement.
COMPENSATION FOR BOOST DC/DC
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 (Inductor current never reaches
zero), 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 produce stability.
INDUCTOR AND DIODE SELECTION
Although the inductor size mentioned earlier is fine for most
applications, a more exact value can be calculated. To en-
sure 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
DSON
is the ON resistance of the internal switch taken from
the graph "R
DSON
vs. V
IN
" 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 corresponding in-
ductor current ripple as shown in
Figure 2
(a) is given by:
The inductor ripple current is important for a few reasons.
One reason is because the peak switch current will be the
average inductor current (input current or I
/D’) plus
i
L
.
As a side note, discontinuous operation occurs when the
inductor current falls to zero during a switching cycle, or
i
L
is greater than the average inductor current. Therefore, con-
tinuous conduction mode occurs when
i
is less 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 inductor must also be sized accordingly. It
should have a saturation current rating higher than the peak
inductor current expected. The output and input voltage
ripples are 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 2
(b). The diode
must be rated for a reverse voltage 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 cur-
rent. During short circuit testing, or if short circuit conditions
are possible in the application, the diode current rating must
20058405
FIGURE 2. (a) Inductor current. (b) Diode current.
L
www.national.com
15
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2715_06 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:TFT Panel Module |
| LM27150 | 制造商:HTC 制造商全稱:HTC Korea TAEJIN Technology Co. 功能描述:1.5A Very L.D.O Voltage Regulator |
| LM27150R-1.5 | 制造商:HTC 制造商全稱:HTC Korea TAEJIN Technology Co. 功能描述:1.5A Very L.D.O Voltage Regulator |
| LM27150R-1.8 | 制造商:HTC 制造商全稱:HTC Korea TAEJIN Technology Co. 功能描述:1.5A Very L.D.O Voltage Regulator |
| LM27150R-12 | 制造商:HTC 制造商全稱:HTC Korea TAEJIN Technology Co. 功能描述:1.5A Very L.D.O Voltage Regulator |
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