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參數(shù)資料
| 型號： | TC7107IPLG |
| 元件分類： | ADC |
| 英文描述： | 1-CH DUAL-SLOPE ADC, PARALLEL ACCESS, PDIP40 |
| 封裝： | 0.600 INCH, PLASTIC, DIP-40 |
| 文件頁數(shù)： | 10/34頁 |
| 文件大?。?/td> | 482K |
| 代理商： | TC7107IPLG |
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TC7106/A/TC7107/A
DS21455D-page 18
2008 Microchip Technology Inc.
9.0
POWER SUPPLIES
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).
FIGURE 9-1:
Generating Negative Supply
From +5V.
In selected applications a negative supply is not
required. The conditions to use a single +5V supply
are:
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
generate -5V from +5V (Figure 9-2).
FIGURE 9-2:
Negative Power Supply
Generation with TC7660.
9.1
TC7107 Power Dissipation
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
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.
FIGURE 9-3:
TC7107 Output Current vs.
Output Voltage.
Notice, however, that once the TC7107A output voltage
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
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
reduce the TC7107A output voltage, when all 24
segments are “ON,” to point “C” of Figure 9-4. When
segments turn off, the output voltage will increase. The
diode, on the other hand, will result in a relatively
steady output voltage, around point “B”.
TC7107A
V+
OSC1
OSC2
OSC3
GND
V-
V+
CD4009
0.047
F
1N914
10
F
–
+
V- = -3.3V
GND
V
IN
-
V
IN
V
REF +
V
REF -
COM
+5V
LED
DRIVE
36
1
35
32
31
30
26
V+
V-
21
TC7660
3
10 F
+
10 F
+
2
8
5
(-5V)
TC7107A
4
V
IN+
C
B
A
6.000
7.000
8.000
9.000
10.000
2.00
2.50
3.00
3.50
4.00
Output Voltage (V)
Out
put
Curren
t(
m
A
)
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