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參數(shù)資料
| 型號： | LM2715MT-ADJ |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 顯示驅(qū)動器 |
| 英文描述： | TFT Panel Module |
| 中文描述： | LIQUID CRYSTAL DISPLAY DRIVER, PDSO16 |
| 封裝： | TSSOP-16 |
| 文件頁數(shù)： | 16/20頁 |
| 文件大?。?/td> | 746K |
| 代理商： | LM2715MT-ADJ |
Operation
(Continued)
exceed the switch current limit. Using Schottky diodes with
lower forward voltage drop will decrease power dissipation
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 LM2715, choosing a crossover point well be-
low where the right half plane zero is located will ensure
sufficient phase margin. A discussion of the right half plane
zero and checking the crossover using the DC gain will
follow.
INPUT AND OUTPUT CAPACITOR SELECTION
The switching action of a boost regulator causes a triangular
voltage waveform at the input. A capacitor is required to
reduce the input ripple and noise for proper operation of the
regulator. The size used depends on the application and
board layout. If the regulator will be loaded uniformly, with
very little load changes, and at lower current outputs, the
input capacitor size can often be reduced. The size can also
be reduced if the input of the regulator is very close to the
source output. The size will generally need to be larger for
applications where the regulator is supplying nearly the
maximum rated output or if large load steps are expected. A
minimum value of 10μF should be used for the less stressful
conditions while a 22μF to 47μF capacitor may be required
for higher power and dynamic loads. Larger values and/or
lower ESR may be needed if the application requires very
low ripple on the input source voltage.
The choice of output capacitors is also somewhat arbitrary
and depends on the design requirements for output voltage
ripple. It is recommended that low ESR (Equivalent Series
Resistance, denoted R
) capacitors be used such as
ceramic, polymer electrolytic, or low ESR tantalum. Higher
ESR capacitors may be used but will require more compen-
sation which will be explained later on in the section. The
ESR is also important because it determines the peak to
peak output voltage ripple according to the approximate
equation:
V
OUT
)
2
i
L
R
ESR
(in Volts)
A minimum value of 10μF is recommended and may be
increased to a larger value.After choosing the output capaci-
tor you can determine a pole-zero pair introduced into the
control loop by the following equations:
Where R
L
is the minimum load resistance corresponding to
the maximum load current. The zero created by the ESR of
the output capacitor is generally very high frequency if the
ESR is small. If low ESR capacitors are used it can be
neglected. If higher ESR capacitors are used see the
High
Output Capacitor ESR Compensation
section.
RIGHT HALF PLANE ZERO
A current mode control boost regulator has an inherent right
half plane zero (RHP zero). This zero has the effect of a zero
in the gain plot, causing an imposed +20dB/decade on the
rolloff, but has the effect of a pole in the phase, subtracting
another 90 in the phase plot. This can cause undesirable
effects if the control loop is influenced by this zero. To ensure
the RHP zero does not cause instability issues, the control
loop should be designed to have a bandwidth of less than
1/6 the frequency of the RHP zero. This zero occurs at a
frequency of:
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 500Hz. The frequency of the pole
created is determined by the equation:
where R
is the output impedance of the error amplifier,
approximately 1M
. Since R
C
is generally much less than
R
O
, it does not have much effect on the above equation and
can be neglected until a value is chosen to set the zero f
ZC
.
f
ZC
is created to cancel out the pole created by the output
capacitor, f
P1
. The output capacitor pole will shift with differ-
ent load currents as shown by the equation, so setting the
zero is not exact. Determine the range of f
P1
over the ex-
pected loads and then set the zero f
ZC
to a point approxi-
mately in the middle. The frequency of this zero is deter-
mined by:
Now R
can be chosen with the selected value for C
.
Check to make sure that the pole f
is still in the 10Hz to
500Hz 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
should be chosen. This will improve the overall bandwidth
which makes the regulator respond more quickly to tran-
sients. If more detail is required, or the most optimal perfor-
mance is desired, refer to a more in depth discussion of
compensating current mode DC/DC switching regulators.
L
www.national.com
16
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
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| LM2715MT-ADJ/NOPB | 功能描述:IC MODULE PANEL TFT DISP 16TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 電源管理 - 專用 系列:- 應(yīng)用說明:Ultrasound Imaging Systems Application Note 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:37 系列:- 應(yīng)用:醫(yī)療用超聲波成像，聲納 電流 - 電源:- 電源電壓:2.37 V ~ 6 V 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:56-WFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:56-TQFN-EP（8x8） 包裝:管件 |
| LM2715MTX-ADJ | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:TFT Panel Module |
| LM2715MTX-ADJ/NOPB | 功能描述:IC MODULE PANEL TFT DISP 16TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 電源管理 - 專用 系列:- 應(yīng)用說明:Ultrasound Imaging Systems Application Note 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:37 系列:- 應(yīng)用:醫(yī)療用超聲波成像，聲納 電流 - 電源:- 電源電壓:2.37 V ~ 6 V 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:56-WFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:56-TQFN-EP（8x8） 包裝:管件 |
| LM2715SQ-ADJ | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:TFT Panel Module |
| LM2715SQ-ADJ/NOPB | 功能描述:IC TFT PANEL MODULE 24-LLP RoHS:是 類別:集成電路 (IC) >> PMIC - 電源管理 - 專用 系列:- 應(yīng)用說明:Ultrasound Imaging Systems Application Note 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:37 系列:- 應(yīng)用:醫(yī)療用超聲波成像，聲納 電流 - 電源:- 電源電壓:2.37 V ~ 6 V 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:56-WFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:56-TQFN-EP（8x8） 包裝:管件 |
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