参数资料
型号: TC7106IKW
厂商: Microchip Technology
文件页数: 18/34页
文件大小: 0K
描述: IC ADC 3 1/2DGT LCD DVR 44MQFP
标准包装: 96
显示器类型: LCD
配置: 7 段显示
数字或字符: A/D,3.5 位数字
电流 - 电源: 800µA
电源电压: 9V
工作温度: -25°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 44-QFP
供应商设备封装: 44-MQFP(10x10)
包装: 托盘
TC7106/A/TC7107/A
9.0
POWER SUPPLIES
9.1
TC7107 Power Dissipation
The TC7107A is designed to work from ±5V supplies.
However, if a negative supply is not available, it can be
generated from the clock output with two diodes, two
capacitors, and an inexpensive IC ( Figure 9-1 ).
V+
CD4009
V+
OSC1
Reduction
The TC7107A sinks the LED display current and this
causes heat to build up in the IC package. If the internal
voltage reference is used, the changing chip
temperature can cause the display to change reading.
By reducing the LED common anode voltage, the
TC7107A package power dissipation is reduced.
Figure 9-3 is a curve tracer display showing the
relationship between output current and output voltage
for a typical TC7107CPL. Since a typical LED has 1.8
OSC2
OSC3
TC7107A
0.047
μF
1N914
10
μF
1N914
+
volts across it at 7 mA, and its common anode is
connected to +5V, the TC7107A output is at 3.2V (point
A on Figure 9-3 ). Maximum power dissipation is
8.1 mA x 3.2V x 24 segments = 622 mW.
GND
V-
10.000
V- = -3.3V
FIGURE 9-1:
Generating Negative Supply
9.000
From +5V.
In selected applications a negative supply is not
required. The conditions to use a single +5V supply
8.000
7.000
C
B
A
are:
? The input signal can be referenced to the center
6.000
of the Common mode range of the converter.
2.00
2.50
3.00
3.50
4.00
? The signal is less than ±1.5V.
Output Voltage (V)
? An external reference is used.
The TSC7660 DC-to-DC converter may be used to
generate -5V from +5V ( Figure 9-2 ).
FIGURE 9-3:
Output Voltage.
TC7107 Output Current vs.
Notice, however, that once the TC7107A output voltage
+5V
1
is above two volts, the LED current is essentially
constant as output voltage increases. Reducing the
output voltage by 0.7V (point B in Figure 9-3 ) results in
7.7 mA of LED current, only a 5 percent reduction.
Maximum power dissipation is only 7.7 mA x 2.5V x 24
= 462 mW, a reduction of 26%. An output voltage
reduction of 1 volt (point C) reduces LED current by
V+ V
LED
DRIVE
REF +
V REF -
COM
TC7107A
V IN +
36
35
32
31
10% (7.3 mA) but power dissipation by 38% (7.3 mA x
2.2V x 24 = 385 mW).
Reduced power dissipation is very easy to obtain.
Figure 9-4 shows two ways: either a 5.1 Ω , 1/4W
resistor, or a 1A diode placed in series with the display
(but not in series with the TC7107A). The resistor will
V IN - 30
V IN
reduce the TC7107A output voltage, when all 24
segments are “ON,” to point “C” of Figure 9-4 . When
8
V-
26
GND
21
segments turn off, the output voltage will increase. The
diode, on the other hand, will result in a relatively
10 μF
+
2
4 TC7660
5
(-5V)
steady output voltage, around point “B”.
3
+ 10 μF
FIGURE 9-2:
Negative Power Supply
Generation with TC7660.
DS21455D-page 18
? 2008 Microchip Technology Inc.
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