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參數(shù)資料
| 型號： | TC815 |
| 廠商： | Microchip Technology Inc. |
| 英文描述： | 3-1/2 Digit Auto-Ranging A/D Converter with Triplex LCD Drive and Display Hold Function |
| 中文描述： | 3-1/2數(shù)字自動測距的A / D三層液晶顯示驅(qū)動器和轉(zhuǎn)換器保持功能 |
| 文件頁數(shù)： | 17/26頁 |
| 文件大?。?/td> | 595K |
| 代理商： | TC815 |
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2002 Microchip Technology Inc.
DS21474B-page 17
TC815
8.0
LOW BATTERY DETECTION
CIRCUIT
The TC815 contains a low battery detector. When the
9V battery supply has been depleted to a 7V nominal
value, the LCD display low battery annunciator is
activated.
The low battery detector is shown in Figure 8-1. The
low battery annunciator remains OFF with the battery
supply greater than 0.7V. The annunciator is ON before
the supply battery has reached 6.3V.
FIGURE 8-1:
LOW BATTERY
DETECTOR
9.0
TRIPLEX LIQUID CRYSTAL
DRIVE
The TC815 directly drives a triplexed liquid crystal dis-
play (LCD) using 1/3 bias drive (see Figure 9-1). All
data, decimal point, polarity and function annunciator
drive signals are developed by the TC815. A direct
connection to a triplex LCD display is possible without
external drive electronics. Standard and custom LCD
displays are readily available from LCD manufacturers.
The LCDs must be driven with an AC signal having
zero DC component for long display life. The liquid
crystal polarization is a function of the RMS voltage
appearing across the backplane and segment driver.
The peak drive signal applied to the LCD is: V
CC
-
V
DISP
.
If V
DISP
, for example, is set at a potential 3V below V
CC
,
the peak drive signal is:
V
P
= V
CC –
V
DISP
= 3V
An “OFF” LCD segment has an RMS voltage of Vp/3
across it or 1 volt. An “ON” segment has a 0.63Vp sig-
nal across it or 1.92V for V
CC –
V
DISP
= 3V.
Since the V
DISP
pin is available, the user may adjust
the “ON” and “OFF” LCD levels for various manufac-
turer’s displays by changing Vp. The liquid crystal
threshold voltage moves down with temperature.
“OFF” segments may become visible at high LCD oper-
ating temperatures. A voltage with a -5 to -20mV/°C
temperature coefficient can be applied to V
DISP
to
accommodate the liquid crystal temperature operating
characteristics, if necessary.
The TC815 internally generates two intermediate LCD
drive potentials (V
H
and V
L
) from a resistive divider
(Figure 9-1), between V
CC
(Pin 28) and V
DISP
(Pin 7).
The ladder impedance is approximately 150k
. This
drive method is commonly known as 1/3 bias. With
V
DISP
connected to digital ground V
P
≈
5.0V.
The intermediate levels are needed so that drive sig-
nals giving RMS “ON” and “OFF” levels can be gener-
ated. Figure 9-2 shows a typical drive signal and the
resulting wave forms for “ON” and “OFF.” RMS voltage
levels across a selected LCD element. Also, see
Figure 9-3 and Table 9-1.
FIGURE 9-1:
1/3 BIAS LCD DRIVE
9.1
LCD Displays
Although most users will design their own custom LCD
display, several manufacturers offer standard displays
for the TC815. Figure 9-3 shows a typical display avail-
able from Varitronix.
1. Varitronix Ltd.
4/F Liven House, 61-63, King Yip Street
Kwun Tong, Hong Kong
Tel: (852)2389-4317
Part No.: VIM 310-1 Pin Connector
VIM 310-2 Elastomer Connector
USA OFFICE:
VL Electronics/Varitronix
3250 Wilshire Blvd. Suite 1901
Los Angeles, CA 90010
Tel: (213) 738-8700
2. Adamant Kogyo Co., LTD
16-7, Shinden, 1-Chome, Adachi-Ku,
Tokyo, 123, Japan
Tel: Tokyo 919-1171
TC815
Comparator
+
–
V
CC
V
SSA
Low Battery Detector
R
2
R
3
To LCD
Annunciator
Selection
Logic
R
1
V
T
V
T
≈
7 X R
1
+ R
2
V
Z
6.2V
R
2
TC815
V
SSA
To Triplex
Segment Drive
Logic
Set V
For Proper V
P
with Resistive
Divider
6
V
H
V
L
50k
50k
50k
28
V
DISP
V
CC
V
P
= V
CC
–
V
DISP
"OFF" = V
P
/3 RMS
"ON3
P
RMS
11
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