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| 型号： | TC7117RCPL |
| 厂商： | Microchip Technology |
| 文件页数： | 12/24页 |
| 文件大小： | 0K |
| 描述： | IC ADC 3 1/2DGT LED DVR REV40DIP |
| 标准包装： | 10 |
| 显示器类型： | LED |
| 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： | 5V |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 通孔 |
| 封装/外壳： | 40-DIP（0.600"，15.24mm） |
| 供应商设备封装： | 40-PDIP |
| 包装： | 管件 |
TC7116/A/TC7117/A
4.0
COMPONENT VALUE
4.5
Oscillator Components
SELECTION
For all frequency ranges, a 100k Ω resistor is recom-
mended; the capacitor is selected from the equation:
4.1
Auto-Zero Capacitor
The size of the auto-zero capacitor has some influence
on system noise. For 200mV full scale, where noise is
very important, a 0.47 μ F capacitor is recommended.
On the 2V scale, a 0.047 μ F capacitor increases the
speed of recovery from overload and is adequate for
EQUATION 4-1:
------ -
f = 0.45
RC
For a 48kHz clock (3 readings per second), C = 100pF.
noise on this scale.
4.6
Reference Voltage
4.2
Reference Capacitor
To generate full scale output (2000 counts), the analog
A 0.1 μ F capacitor is acceptable in most applications.
However, where a large Common mode voltage exists
(i.e., the V IN - pin is not at analog common), and a
200mV scale is used, a larger value is required to pre-
vent rollover error. Generally, 1 μ F will hold the rollover
error to 0.5 count in this instance.
input requirement is V IN = 2V REF . Thus, for the 200mV
and 2V scale, V REF should equal 100mV and 1V,
respectively. In many applications, where the ADC is
connected to a transducer, a scale factor exists
between the input voltage and the digital reading. For
instance, in a measuring system, the designer might like
to have a full scale reading when the voltage from the
4.3
Integrating Capacitor
transducer is 700mV. Instead of dividing the input down
to 200mV, the designer should use the input voltage
The integrating capacitor should be selected to give the
maximum voltage swing that ensures tolerance buildup
will not saturate the integrator swing (approximately
0.3V from either supply). In the TC7116/TC7116A or
the TC7117/TC7117A, when the analog common is
used as a reference, a nominal ±2V full scale integrator
swing is acceptable. For the TC7117/TC7117A, with
±5V supplies and analog common tied to supply
ground, a ±3.5V to ±4V swing is nominal. For 3 read-
ings per second (48kHz clock), nominal values for C INT
are 0.22 μ 1F and 0.10 μ F, respectively. If different oscil-
lator frequencies are used, these values should be
changed in inverse proportion to maintain the output
swing. The integrating capacitor must have low dielec-
tric absorption to prevent rollover errors. Polypropylene
capacitors are recommended for this application.
directly and select V REF = 350mV. Suitable values for
integrating resistor and capacitor would be 120kW and
0.22 μ F. This makes the system slightly quieter and also
avoids a divider network on the input. The TC7117/
TC7117A, with ±5V supplies, can accept input signals
up to ±4V. Another advantage of this system is when a
digital reading of zero is desired for V IN ≠ 0. Tempera-
ture and weighing systems with a variable tare are
examples. This offset reading can be conveniently gen-
erated by connecting the voltage transducer between
V IN + and analog common, and the variable (or fixed)
offset voltage between analog common and V IN -.
4.4
Integrating Resistor
Both the buffer amplifier and the integrator have a class
A output stage with 100 μ A of quiescent current. They
can supply 20 μ A of drive current with negligible non-
linearity. The integrating resistor should be large
enough to remain in this very linear region over the
input voltage range, but small enough that undue leak-
age requirements are not placed on the PC board. For
2V full scale, 470k Ω is near optimum and, similarly,
47k Ω for 200mV full scale.
DS21457C-page 12
? 2006 Microchip Technology Inc.
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