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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： | 11/24页 |
| 文件大小： | 185K |
| 代理商： | TC820CPL |
19
TC820
3-3/4 A/D Converter with Frequency
Counter and Logic Probe
TC820-10 10/17/96
2001 Microchip Technology Inc.
DS21476A
Figure 18. Reference Voltage Connections
Figure 20. Frequency Counter External Buffer
Logic Probe Inputs
The DP0/LO and DP1/HI inputs provide the logic probe
inputs when the LOGIC input is high. Driving either DP0/
LO or DP1/HI to a logic high will turn on the appropriate
LCD annunciator. When DP0/LO is high, the buzzer will
be on.
To provide a "single input" logic probe function, exter-
nal buffers should be used. A simple circuit is shown in
Figure 21. This circuit will turn the appropriate annunciator
on for high and low level inputs.
If carefully controlled logic thresholds are required, a
window comparator can be used. Figure 22 shows a typi-
cal circuit. This circuit will turn on the high or low annuncia-
tors when the logic thresholds are exceeded, but the resis-
tors connected from DP0/LO and DP1/HI to DGND will turn
both annunciators off when the logic probe is unconnected.
The TC820 logic inputs are not latched internally, so
pulses of short duration will usually be difficult or impos-
sible to see. To display short pulses properly, the input
Figure 21. Simple External Logic Probe Buffer
applied to the reference input. If the unknown equals the
standard, the input voltage will equal the reference voltage
and the display will read 2000. The displayed reading can
be determined from the following expression:
Displayed reading =
2000
The display will overrange for values of RUNKNOWN ≥ 2
RSTANDARD.
Buffering the FREQ Input
When the FREQ/VOLTS input is high and the LOGIC
input is low, the TC820 will count pulses at the RANGE/
FREQ input. The time base will be fOSC/40,000, or 1 sec-
ond with a 40kHz clock. The signal to be measured should
swing from VDD to DGND. The RANGE/FREQ input has
CMOS input levels without hysteresis. For best results,
especially with low-frequency sine-wave inputs, an exter-
nal buffer with hysteresis should be added. A typical circuit
is shown in Figure 20.
Figure 19. Low Parts Count Ratiometric Resistance Measurement
VDD
TC820
LOGIC
PROBE
INPUT
+9V
74HC14
LOGIC
DP1/HI
DP0/LO
DGND
*
9V
TC820
+
22k
VDD
VSS
V
+
REF
V
–
REF
ANALOG
COMMON
SET V
= 1/2 V
REF
FULL SCALE
(a) Internal Reference
(b) External Reference
V
+
REF
V
–
REF
COMMON
V
+
TC04A
1.2V
REF
2k
V
REF
2k
TC820
+
DGND
FREQUENCY
INPUT
GND
DGND
74HC14
RANGE/FREQ
FREQ/VOLTS
VDD
1
F
+9V
RUNKNOWN
RSTANDARD
TC820
RSTANDARD
RUNKNOWN
ANALOG
COMMON
VDD
V
+
REF
V
–
REF
V
+
IN
V
–
IN
LCD
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