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参数资料
| 型号： | ICM7211AMLPL |
| 厂商： | INTERSIL CORP |
| 元件分类： | 显示驱动器 |
| 英文描述： | 4-Digit, LCD Display Driver |
| 中文描述： | LIQUID CRYSTAL DISPLAY DRIVER, PDIP40 |
| 封装： | PLASTIC, DIP-40 |
| 文件页数： | 9/12页 |
| 文件大小： | 83K |
| 代理商： | ICM7211AMLPL |
9-14
Description Of Operation
LCD Devices
The LCD devices in the family (ICM7211, ICM7211A,
ICM7211M, ICM7211AM) provide outputs suitable for driving
conventional four-digit, seven-segment LCD displays. These
devices include 28 individual segment drivers, backplane
driver, and a self-contained oscillator and divider chain to
generate the backplane frequency.
The segment and backplane drivers each consist of a
CMOS inverter, with the N-Channel and P-Channel devices
ratioed to provide identical on resistances, and thus equal
rise and fall times. This eliminates any DC component, which
could arise from differing rise and fall times, and ensures
maximum display life.
The backplane output devices can be disabled by connect-
ing the OSCillator input (pin 36) to V
SS
. This allows the 28
segment outputs to be synchronized directly to a signal input
at the BP terminal (pin 5). In this manner, several slave
devices may be cascaded to the backplane output of one
master device, or the backplane may be derived from an
external source. This allows the use of displays with charac-
ters in multiples of four and a single backplane. A slave
device represents a load of approximately 200pF (compara-
ble to one additional segment). Thus the limitation of the
number of devices that can be slaved to one master device
backplane driver is the additional load represented by the
larger backplane of displays of more than four digits. A good
rule of thumb to observe in order to minimize power con-
sumption is to keep the backplane rise and fall times less
than about 5
μ
s. The backplane output driver should handle
the backplane to a display of 16 one-half inch characters. It
is recommended, if more than four devices are to be slaved
together, the backplane signal be derived externally and all
the ICM7211 devices be slaved to it. This external signal
should be capable of driving very large capacitive loads with
short (1 - 2
μ
s) rise and fall times. The maximum frequency
for a backplane signal should be about 150Hz although this
may be too fast for optimum display response at lower dis-
play temperatures, depending on the display type.
The onboard oscillator is designed to free run at approxi-
mately 19kHz at microampere current levels. The oscillator
frequency is divided by 128 to provide the backplane fre-
quency, which will be approximately 150Hz with the oscillator
free-running; the oscillator frequency may be reduced by
connecting an external capacitor between the OSCillator ter-
minal and V
DD
.
The oscillator may also be overdriven if desired, although care
must be taken to ensure that the backplane driver is not dis-
abled during the negative portion of the overdriving signal
(which could cause a DC component to the display). This can
be done by driving the OSCillator input between the positive
supply and a level out of the range where the backplane disable
is sensed (about one fifth of the supply voltage above V
SS
).
Another technique for overdriving the oscillator (with a signal
swinging the full supply) is to skew the duty cycle of the over-
driving signal such that the negative portion has a duration
shorter than about one microsecond. The backplane disable
sensing circuit will not respond to signals of this duration.
LED Devices
The LED device in the family (ICM7212AM) provides outputs
suitable for directly driving four-digit, seven-segment
common-anode LED displays. These devices include 28
individual segment drivers, each consisting of a low-leakage,
current-controlled, open-drain, N-Channel transistor.
The drain current of these transistors can be controlled by
varying the voltage at the BRtrighTness input (pin 5). The volt-
age at this pin is transferred to the gates of the output devices
for “on” segments, and thus directly modulates the transistor’s
“on” resistance. A brightness control can be easily imple-
mented with a single potentiometer controlling the voltage at
pin 5, connected as in Figure 9. The potentiometer should be
a high value (100k
to 1M
) to minimize power consumption,
which can be significant when the display is off.
The brightness input may also be operated digitally as a dis-
play enable; when high, the display is fully on, and low fully
off. The display brightness may also be controlled by varying
the duty cycle of a signal swinging between the two voltages
at the brightness input.
Note that the LED device has two connections for V
SS
; both
of these pins should be connected. The double connection is
necessary to minimize effects of bond wire resistance with
the large total display currents possible.
When operating LED devices at higher temperatures and/or
higher supply voltages, the device power dissipation may
need to be reduced to prevent excessive chip temperatures.
The maximum power dissipation is 1W at 25
o
C, derated lin-
early above 35
o
C to 500mW at 70
o
C (-15mW/
o
C above
35
o
C). Power dissipation for the device is given by:
P = (V
SUPP
- V
FLED
)(l
SEG
)(n
SEG
)
where V
FLED
is the LED forward voltage drop, I
SEG
is
segment current, and n
SEG
is the number of “on” segments.
It is recommended that if the device is to be operated at
OSCILLATOR
FREQUENCY
BACKPLANE
INPUT/OUTPUT
OFF
ON
64 CYCLES
64 CYCLES
128 CYCLES
SEGMENTS
SEGMENTS
FIGURE 8. DISPLAY WAVEFORMS
100k
TO 1M
BRIGHTNESS
PIN 5
V
DD
(LED ANODES)
FIGURE 9. BRIGHTNESS CONTROL
ICM7211, ICM7212
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相关代理商/技术参数 |
参数描述 |
|---|---|
| ICM7211AMLPLZ | 制造商:INTERSIL 制造商全称:Intersil Corporation 功能描述:4-Digit, LCD Display Driver |
| ICM7211CQH | 制造商:未知厂家 制造商全称:未知厂家 功能描述:LCD Display Driver |
| ICM7211I/D | 制造商:未知厂家 制造商全称:未知厂家 功能描述:LCD Display Driver |
| ICM7211I/D+ | 功能描述:LCD 驱动器 RoHS:否 制造商:Maxim Integrated 数位数量:4.5 片段数量:30 最大时钟频率:19 KHz 工作电源电压:3 V to 3.6 V 最大工作温度:+ 85 C 最小工作温度:- 20 C 封装 / 箱体:PDIP-40 封装:Tube |
| ICM7211IJL | 功能描述:LCD 驱动器 4 DIGIT DISPLAY DECODER/DRVRS RoHS:否 制造商:Maxim Integrated 数位数量:4.5 片段数量:30 最大时钟频率:19 KHz 工作电源电压:3 V to 3.6 V 最大工作温度:+ 85 C 最小工作温度:- 20 C 封装 / 箱体:PDIP-40 封装:Tube |
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