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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)： | 17/20頁(yè) |
| 文件大?。?/td> | 746K |
| 代理商： | LM2715 |
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Operation
(Continued)
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
ZC
.
CHECKING THE DESIGN
The final step is to check the design. This is to ensure a
bandwidth of 1/6 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 less than 1/6 the RHP zero, the
phase margin should be high enough for stability. The phase
margin can also be improved by adding C
C2
as discussed
earlier in the section. The equation for A
is given below
with additional equations required for the calculation:
mc
)
0.181fs (in V/s)
where R
is the minimum load resistance, V
is the mini-
mum input voltage, g
m
is the error amplifier transconduc-
tance found in the
Electrical Characteristics
table, and R
D-
SON
is the value chosen from the graph "R
vs. V
IN
" in
the
Typical Performance Characteristics
section.
LAYOUT CONSIDERATIONS
Vcom AND Gamma
If the supply input, AV
IN
, of the Vcom amplifier and Gamma
buffer is tied directly to the output of the boost DC/DC
converter, a 100nF bypass capacitor should be connected
close to the device between AV
IN
and PGND. If the AV
IN
supply is connected to an external source, a larger bypass
capacitor may be required for desired performance depend-
ing on the external supply voltage ripple and noise.
The Gamma buffer and Vcom amplifier input signal traces
should be routed away from the SW pin. Routing these
traces near the SW pin may inject noise into the device and
affect the performance of the amplifier and/or buffer. If resis-
tor dividers are used to drive the inputs of either the Vcom
amplifier or Gamma buffer the ground connections for them
should be made to AGND to minimize noise.
BOOST SWITCHING REGULATOR
The LM2715 uses two ground connections, PGND and
AGND. The feedback, delay, and compensation networks
should be connected directly to their own dedicated analog
ground plane and this ground plane must connect to the
AGND pin, as shown in
Figure 3
. No other circuits should
connect to this AGND plane. If no analog ground plane is
available then the ground connections of the feedback, de-
lay, and compensation networks must tie directly to the
AGND pin, as show in
Figure 4
. Connecting these networks
to the PGND plane can inject noise into the system and
effect performance.
The input bypass capacitor C
IN
must be placed close to the
device and should connect between V
IN
and PGND. This will
reduce copper trace resistance which effects input voltage
ripple of the IC. For additional input voltage filtering, a 100nF
bypass capacitor can be placed in parallel with C
IN
, close to
the V
IN
pin, to shunt any high frequency noise to ground. The
output capacitor, C
OUT
, should also be placed close to the
device and should connect between V
OUT
and PGND. Any
copper trace connections for the C
capacitor can in-
crease the series resistance, which directly effects output
voltage ripple and efficiency. The feedback network, resis-
tors R1 and R2, should be kept close to the FB pin, and
away from the inductor, to minimize copper trace connec-
tions that can inject noise into the system. Trace connections
made to the inductor and schottky diode should be mini-
mized to reduce power dissipation and increase overall effi-
ciency.
The AGND and PGND pins must connect directly to each
other at the device as shown in
Figure 3
and
Figure 4
.
Failure to do so may affect the performance of the LM2715
and limit its output current capability.
L
www.national.com
17
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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 |
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| 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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