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参数资料
| 型号： | TC820CPL |
| 元件分类： | ADC |
| 英文描述： | 1-CH DUAL-SLOPE ADC, PDIP40 |
| 封装： | PLASTIC, DIP-40 |
| 文件页数： | 10/24页 |
| 文件大小： | 185K |
| 代理商： | TC820CPL |
18
3-3/4 A/D Converter with Frequency
Counter and Logic Probe
TC820
TC820-10 10/17/96
2001 Microchip Technology Inc.
DS21476A
Figure 17. System Clock Generation
maintain the nominal
±2V integrator swing. An exact
expression for CINT is:
CINT =
where: fOSC = Clock frequency
VFS = Full-scale input voltage
RINT = Integrating resistor
VINT = Desired full-scale integrator output swing
CINT must have low dielectric absorption to minimize
roll-over error. A polypropylene capacitor is recommended.
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 400mV full scale, RINT should
be about 100k
.
Reference Voltage Selection
A full-scale reading (4000 counts for TC820) requires
the input signal be twice the reference voltage.
Table III. Reference Voltage Selection
Full-Scale
Input Voltage
(VFS) (Note 1)
VREF
Resolution
200mV
Note 2
–
400mV
200mV
10
V
1V
500mV
250
V
2V
1V
500
V
(Notes 3, 4)
NOTES: 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 "10:1 Range Change" section.
4. Full-scale voltage values are not limited to the values
shown. For example, TC820 VFS can be any value from
400mV to 2V.
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 pres-
sure transducer output is 800mV for 4000 lb/in2. Rather
than dividing the input voltage by two, the reference volt-
age should be set to 400mV. This permits 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 when-
ever the supply potential is greater than approximately 7V.
The low-battery detection circuit and analog common oper-
ate 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 refer-
ence. Figure 18 shows internal and external reference
applications.
Ratiometric Resistance Measurements
The TC820 true differential input and differential refer-
ence make ratiometric readings possible. In ratiometric
operation, an unknown resistance is measured with re-
spect to a known standard resistance. No accurately de-
fined reference voltage is needed.
The unknown resistance is put in series with a known
standard and a current is passed through the pair (Fig-
ure 19). The voltage developed across the unknown is
applied to the input and voltages across the known resistor
A/D
COUNTER
TC820
÷40,000
COUNTER
TIME BASE
÷240
LCD
BACKPLANE
DRIVER
÷8
BUZZER
÷2
OSC1
OSC2
OSC3
XTAL
OSCILLATOR
COMPONENTS
R/C
OSCILLATOR
COMPONENTS
4000 VFS
VINT RINT fOSC
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