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參數(shù)資料
| 型號(hào)： | LM8207 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | TFT 18 Gamma Buffer + VCOM Driver + Voltage Reference |
| 中文描述： | 液晶18伽瑪緩沖器的VCOM驅(qū)動(dòng)電壓基準(zhǔn) |
| 文件頁數(shù)： | 16/22頁 |
| 文件大?。?/td> | 1393K |
| 代理商： | LM8207 |
Application Section
(Continued)
TABLE 1. Resistor Values for Defining the Gamma
Correction Curve
Gamma Curve Definition
VGMA Voltage
VGMA
Node
Calculated Resistance (
)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
11.59
11.38
9.18
8.51
7.84
7.41
7.13
6.15
6.07
5.90
5.82
4.84
4.56
4.13
3.46
2.73
0.54
0.33
210
2200
670
670
430
280
980
80
170
80
980
280
430
670
730
2190
210
330
Changing the gamma correction curve, in combination with
the load of the column drivers can impact the behavior of the
gamma buffers. Gamma buffers 1 and 2 are designed for
operating voltages near V
, and will source the current into
the column drivers. Gamma buffers 17 and 18 are designed
for operating voltages near V
SS
and will sink this current.
Buffers 3 to 16 are designed to operate in the mid-voltage
range and can sink or source current. Under special circum-
stances, by increasing the voltage gap between gamma
buffer 1 and gamma buffer 2, in combination with a low
impedance load of the column driver between these outputs,
the output of buffer 2 has to sink more current than possible,
and can saturate. This will result in a setting error of the
inputs of the column driver.
For buffer 17 and 18 an identical situation can occur, by
increasing the operating voltage range of buffer 17 with
respect to buffer 18.
Asimple and cost effective solution is to lower the resistance
between buffer 2 and 3 or buffer 16 and 17, using an
additional by-pass resistor R
. This method is presented in
Figure 10
. This will not affect the desired voltage levels, and
buffer 3 which has a larger linear output current spec will sink
the current instead of buffer 2. The resistor value R
can be
calculated by the voltage drop divided by the current. The
resistor value should be low enough to sink this current,
otherwise buffer 2 and/or buffer 17 will still saturate.
GAMMA VOLTAGE ACCURACY
Adding buffers to the tabs of the gamma correction resistor
chain will make the values more independent of the load
variations. Unfortunately, there are some other effects that
will influence the gamma values. The following effects deter-
mine the accuracy of each gamma voltage.
Major effects are:
Variation of the internal voltage reference. This can be
found in the Electrical Characteristics Table. This is the
maximum variation between parts.
Variation of the feedback resistors used for setting the
output voltage of the voltage reference (OUT_V
REF
). Us-
ing high accuracy resistors will result in a small variation
of the output voltage between different boards
The accuracy of the resistors obtained from the gamma
correction voltage curve. The gamma correction curve
will be affected by the accuracy of the resistors. This will
vary over different boards. Temperature variations will not
affect this curve.
Output offset voltage (V
) of the buffers. Variations of
V
(output offset voltage) of the buffers, will affect the
gamma correction curve. The contribution of V
is
higher for the buffers driving the lower gamma voltages.
Minor effects are:
Input current (I
) of the gamma buffers. Variations of
the input current (I
) of the gamma buffers caused by
temperature changes, will affect the gamma correction
voltages.
20137946
FIGURE 10. Using additional by-pass resistor to
increase current sinking capability
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 |
|---|---|
| LM8207MT | 功能描述:LCD 驅(qū)動(dòng)器 RoHS:否 制造商:Maxim Integrated 數(shù)位數(shù)量:4.5 片段數(shù)量:30 最大時(shí)鐘頻率:19 KHz 工作電源電壓:3 V to 3.6 V 最大工作溫度:+ 85 C 最小工作溫度:- 20 C 封裝 / 箱體:PDIP-40 封裝:Tube |
| LM8207MT/NOPB | 功能描述:LCD Gamma緩沖器 RoHS:否 制造商:Maxim Integrated 輸入補(bǔ)償電壓: 轉(zhuǎn)換速度: 電源電壓-最大:20 V 電源電壓-最小:9 V 電源電流: 最大功率耗散: 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFN-38 封裝:Tube |
| LM8207MTX | 功能描述:LCD 驅(qū)動(dòng)器 RoHS:否 制造商:Maxim Integrated 數(shù)位數(shù)量:4.5 片段數(shù)量:30 最大時(shí)鐘頻率:19 KHz 工作電源電壓:3 V to 3.6 V 最大工作溫度:+ 85 C 最小工作溫度:- 20 C 封裝 / 箱體:PDIP-40 封裝:Tube |
| LM8207MTX/NOPB | 功能描述:LCD 驅(qū)動(dòng)器 RoHS:否 制造商:Maxim Integrated 數(shù)位數(shù)量:4.5 片段數(shù)量:30 最大時(shí)鐘頻率:19 KHz 工作電源電壓:3 V to 3.6 V 最大工作溫度:+ 85 C 最小工作溫度:- 20 C 封裝 / 箱體:PDIP-40 封裝:Tube |
| LM825 | 制造商:Pulse Electronics Corporation 功能描述: |
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