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參數(shù)資料
| 型號(hào)： | ICM7232BFIPL |
| 廠商： | HARRIS SEMICONDUCTOR |
| 元件分類： | 顯示驅(qū)動(dòng)器 |
| 英文描述： | LED AMBER DIFF 2MM RND TOP VIEW |
| 中文描述： | LIQUID CRYSTAL DISPLAY DRIVER, PDIP40 |
| 文件頁數(shù)： | 10/16頁 |
| 文件大?。?/td> | 103K |
| 代理商： | ICM7232BFIPL |
9-28
Figure 8 shows the curve of contrast versus applied RMS volt-
age for a liquid crystal material tailored for V
PEAK
= 3.1V, a
typical value for
1
/
3
multiplexed displays in calculators. Note
that the RMS OFF voltage V
PEAK
/3
≈
1V is just below the
“threshold” voltage where contrast begins to increase. This
places the RMS ON voltage at 2.1V, which provides about
85% contrast when viewed straight on.
All members of the ICM7231 and ICM7232 family use an internal
resistor string of three equal value resistors to generate the volt-
ages used to drive the display. One end of the string is connected
on the chip to V
DD
and the other end (user input) is available at
pin 2 (V
DISP
) on each chip. This allows the display voltage input
(V
DISP
) to be optimized for the particular liquid crystal material
used. Remember that V
PEAK
= V
DD
- V
DISP
and should be
three times the threshold voltage of the liquid crystal material
used. Also it is very important that pin 2 never be driven below
V
SS
. This can cause device latchup and destruction of the chip.
Temperature Effects and Temperature Compensation
The performance of the LCD material is affected by tempera-
ture in two ways. The response time of the display to changes
of applied RMS voltage gets longer as the display tempera-
ture drops. At very low temperatures (-20
o
C) some displays
may take several seconds to change a new character after the
new information appears at the outputs. However, for most
applications above 0
o
C this will not be a problem with avail-
able multiplexed LCD materials, and for low-temperature
applications, high-speed liquid crystal materials are available.
At high temperature, the effect to consider deals with plastic
materials used to make the polarizer.
Some polarizers become soft at high temperatures and per-
manently lose their polarizing ability, thereby seriously
degrading display contrast. Some displays also use sealing
materials unsuitable for high temperature use. Thus, when
specifying displays the following must be kept in mind: liquid
crystal material, polarizer, and seal materials.
A more important effect of temperature is the variation of
threshold voltage. For typical liquid crystal materials suitable for
multiplexing, the peak voltage has a temperature coefficient of -7
to -14mV/
o
C. This means that as temperature rises, the thresh-
old voltage goes down. Assuming a fixed value for V
P
, when the
threshold voltage drops below V
PEAK
/3 OFF segments begin to
be visible. Figure 9 shows the temperature dependence of peak
voltage for the same liquid crystal material of Figure 8.
For applications where the display temperature does not
vary widely, V
PEAK
may be set at a fixed voltage chosen to
make the RMS OFF voltage, V
PEAK
/3, just below the thresh-
old voltage at the highest temperature expected. This will
prevent OFF segments turning ON at high temperature (this
at the cost of reduced contrast for ON segments at low
temperatures).
For applications where the display temperature may vary to
wider extremes, the display voltage V
DISP
(and thus V
PEAK
)
may require temperature compensation to maintain sufficient
contrast without OFF segments becoming visible.
Display Voltage and Temperature Compensation
These circuits allow control of the display peak voltage by
bringing the bottom of the voltage divider resistor string out at
pin 2. The simplest means for generating a display voltage
suitable to a particular display is to connect a potentiometer
from pin 2 to V
SS
as shown in Figure 10. A potentiometer with
a maximum value of 200k
should give sufficient range of
adjustment to suit most displays. This method for generating
display voltage should be used only in applications where the
temperature of the chip and display won’t vary more than
±
5
o
C (
±
9
o
F), as the resistors on the chip have a positive tem-
perature coefficient, which will tend to increase the display
peak voltage with an increase in temperature. The display
voltage also depends on the power supply voltage, leading to
tighter tolerances for wider temperature ranges.
APPLIED VOLTAGE (V
RMS
)
C
100
90
80
70
60
50
40
30
20
10
0
T
A
= 25
o
C
θ
= -10
o
θ
= -30
o
θ
= 0
V
ON
= 2.1V
0
1
2
3
4
θ
= +10
o
V
OFF
=
1.1V
RMS
0-
0+
FIGURE 8. CONTRAST vs APPLIED RMS VOLTAGE
AMBIENT TEMPERATURE (
o
C)
6
5
4
3
2
1
0
-10
0
10
20
30
40
50
PEAK VOLTAGE FOR
90% CONTRAST (ON)
PEAK VOLTAGE FOR
10% CONTRAST (OFF)
P
FIGURE 9. TEMPERATURE DEPENDENCE OF LC THRESHOLD
ICM7231, ICM7232
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相關(guān)代理商/技術(shù)參數(shù) |
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| ICM7232CFIPL | 制造商:INTERSIL 制造商全稱:Intersil Corporation 功能描述:TIMERS COUNTERS AND DISPLAY DRIVERS |
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| ICM7232D WAF | 制造商:Harris Corporation 功能描述: |
| ICM7232FIPL | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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