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TC7106A 参数 Datasheet PDF下载

TC7106A图片预览
型号: TC7106A
PDF下载: 下载PDF文件 查看货源
内容描述: 3-1 / 2位A / D转换器 [3-1/2 DIGIT A/D CONVERTERS]
分类和应用: 转换器
文件页数/大小: 19 页 / 296 K
品牌: TELCOM [ TELCOM SEMICONDUCTOR, INC ]
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3-1/2 DIGIT A/D CONVERTERS  
TC7106  
TC7106A  
TC7107  
TC7107A  
POWER SUPPLIES  
TC7107 Power Dissipation Reduction  
The TC7107A is designed to work from ±5V supplies.  
However, if a negative supply is not available, it can be  
generatedfromtheclockoutputwithtwodiodes,twocapaci-  
tors, and an inexpensive IC. (Figure 12)  
In selected applications a negative supply is not re-  
quired. The conditions to use a single +5V supply are:  
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.  
The input signal can be referenced to the center of the  
common-mode range of the converter.  
The signal is less than ±1.5V.  
An external reference is used.  
The TSC7660 DC to DC converter may be used to  
Figure 14 is a photograph of a curve-tracer display  
showing the relationship between output current and output  
voltage for a typical TC7107CPL. Since a typical LED has  
1.8 volts across it at 7mA, and its common anode is con-  
nected to +5V, the TC7107A output is at 3.2V (point A on  
Figure 13). Maximum power dissipation is 8.1mA x 3.2V x  
24 segments = 622mW.  
Notice, however, that once the TC7107A output voltage  
isabovetwovolts, theLEDcurrentisessentiallyconstantas  
output voltage increases. Reducing the output voltage by  
0.7V (point B in Figure 14) results in 7.7mA of LED current,  
only a 5 percent reduction. Maximum power dissipation is  
only 7.7mA x 2.5 V x 24 = 462mW, a reduction of 26%. An  
output voltage reduction of 1 volt (point C) reduces LED  
current by 10% (7.3mA) but power dissipation by 38%!  
(7.3mA x 2.2V x 24 = 385mW).  
generate – 5 V from +5 V (Figure 13).  
+
V
CD4009  
+
V
OSC  
1
OSC  
0.047  
µF  
2
1N914  
+
OSC  
3
10  
µF  
1N914  
TC7107A  
GND  
V
V
= –3.3V  
Figure 12. Generating Negative Supply From +5 V  
+5 V  
1
+
36  
35  
32  
+
V
V
V
REF  
REF  
LED  
DRIVE  
Figure 14. TC7107A Output Current vs Output Voltage  
COM  
TC7107A  
Reduced power dissipation is very easy to obtain.  
Figure15showstwoways:eithera5.1ohm,1/4wattresistor  
or a 1 Amp diode placed in series with the display (but not in  
series with the TC7107A). The resistor will reduce the  
TC7107A output voltage, when all 24 segments are “ON,” to  
point “C” of Figure 14. When segments turn off, the output  
voltagewillincrease.Thediode,ontheotherhand,willresult  
in a relatively steady output voltage, around point “B.”  
In addition to limiting maximum power dissipation, the  
resistor reduces the change in power dissipation as the  
display changes. This effect is caused by the fact that, as  
+
31  
V
IN  
V
IN  
IN  
30  
21  
V
GND  
V
8
26  
2
4
+
(–5 V)  
5
10µF  
TC7660  
*3-1/2 DIGIT ADC  
3
+
10µF  
Figure 13. Negative Power Supply Generation with TC7660  
3-196  
TELCOM SEMICONDUCTOR, INC.