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参数资料
| 型号： | TC820C/KW |
| 元件分类： | ADC |
| 英文描述： | 1-CH 3-BIT DUAL-SLOPE ADC, PARALLEL ACCESS, PQFP44 |
| 封装： | 10 X 10 MM, 2 MM HEIGHT, PLASTIC, MQFP-44 |
| 文件页数： | 11/34页 |
| 文件大小： | 435K |
| 代理商： | TC820C/KW |
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2007 Microchip Technology Inc.
DS21476C-page 19
TC820
5.6.3
INTEGRATING CAPACITOR - CINT
CINT should be selected to maximize integrator output
voltage swing without causing output saturation. Analog
common will normally supply the differential voltage
reference. For this case, a ±2V integrator output swing is
optimum when the analog input is near full scale. For 2.5
readings/second (FOSC = 40 kHz) and VFS = 400 mV, a
0.22 F value is suggested. If a different oscillator
frequency is used, CINT must be changed in inverse
proportion to maintain the nominal ±2V integrator
swing.
An exact expression for CINT is:
EQUATION 5-2:
CINT must have low dielectric absorption to minimize
rollover
error.
A
polypropylene
capacitor
is
recommended.
5.6.4
INTEGRATING RESISTOR - RINT
The input buffer amplifier and integrator are designed
with class A output stages. The integrator and buffer
can supply 40 A drive currents with negligible linearity
errors. RINT is chosen to remain in the output stage
linear drive region, but not so large that printed circuit
board leakage currents induce errors. For a 400 mV
full-scale, RINT should be about 100 kΩ.
5.7
Reference Voltage Selection
A full-scale reading (4000 counts for TC820) requires
the input signal be twice the reference voltage. See
Reference Voltage Selection, Table 5-1 below.
TABLE 5-1:
REFERENCE VOLTAGE
SELECTION
In some applications, a scale factor other than unity
may exist between a transducer output voltage and the
required digital reading. Assume, for example, that a
pressure transducer output is 800 mV for 4000 lb/in2.
Rather than dividing the input voltage by two, the
reference voltage should be set to 400 mV. This per-
mits the transducer input to be used directly.
The internal voltage reference potential available at
analog common will normally be used to supply the
converter's reference voltage. This potential is stable
whenever
the
supply
potential
is
greater
than
approximately 7V. The low battery detection circuit and
analog common operate from the same internal
reference. This ensures that the low battery annunciator
will turn on at the time the internal reference begins to
lose regulation.
The TC820 can also operate with an external
reference. Figure 5-7 shows internal and external ref-
erence applications.
FIGURE 5-7:
Reference Voltage
Connections.
CINT =
4000 VFS
VINT RINT FOSC
Where:
FOSC
=
Clock Frequency
VFS
=
Full-Scale Input Voltage
RINT
=
Integrating Resistor
VINT
=
Desired Full-Scale Integrator
Output Swing
Full Scale Input Voltage
(VFS) (Note 1)
VREF
Resolution
200 mV
(Note 2)
—
400 mV
200 mV
10 V
1V
500 mV
250 V
2V (Notes 3, 4)
1V
500 V
Note 1:
TC820 in A/D Converter mode, RANGE/
FREQ = logic low.
2:
Not recommended.
3:
VFS > 2V may exceed the Input Common
mode range. See Section 3.2.7 “10:1
4:
Full-scale voltage values are not limited to
the values shown. For example, TC820
VFS can be any value from 400 mV to 2V.
9V
TC820
+
22k
Ω
VDD
VSS
VREF+
VREF-
Analog
Common
SET VREF = 1/2 VFULL SCALE
(a) Internal Reference
(b) External Reference
VREF+
VREF-
Analog
Common
V+
2k
Ω
VREF
VIN
VOUT
VSS
MCP1525
1
μF
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