參數(shù)資料
型號(hào): TC820
廠商: TelCom Semiconductor, Inc.
元件分類(lèi): 通用總線(xiàn)功能
英文描述: 3-3/4 DIGIT A/D CONVERTER WITH FREQUENCY COUNTER AND LOGIC PROBE
中文描述: 3-3/4數(shù)字A / D轉(zhuǎn)換頻率計(jì)數(shù)器和邏輯探針轉(zhuǎn)爐
文件頁(yè)數(shù): 19/22頁(yè)
文件大?。?/td> 275K
代理商: TC820
3-167
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
V
DD
TC820
LOGIC
PROBE
INPUT
+9V
74HC14
LOGIC
DP1/HI
DP0/LO
DGND
*
*
*
TC820
3-3/4 A/D CONVERTER WITH
FREQUENCY COUNTER
AND LOGIC PROBE
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, external
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 typical
circuit. This circuit will turn on the high or low annunciators
when the logic thresholds are exceeded, but the resistors
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 impossible
to see. To display short pulses properly, the input pulse
should be "stretched." The circuit of Figure 22 shows cap-
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 =
3
2000
The display will overrange for values of R
UNKNOWN
2
3
R
STANDARD
.
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 f
OSC
/40,000, or 1 second
with a 40kHz clock. The signal to be measured should swing
from V
DD
to DGND. The RANGE/FREQ input has CMOS
input levels without hysteresis. For best results, especially
with low-frequency sine-wave inputs, an external buffer with
hysteresis should be added. A typical circuit is shown in
Figure 20.
Figure 19. Low Parts Count Ratiometric Resistance Measurement
9V
TC820
TC820
+
22k
V
DD
V
DD
V
SS
V
+
V
ANALOG
COMMON
SET V = 1/2 V
(a) Internal Reference
FULL SCALE
(b) External Reference
V
+
V
REF
COMMON
V
+
TC04A
1.2V
REF
2k
V
REF
2k
TC820
+
DGND
FREQUENCY
INPUT
GND
DGND
74HC14
RANGE/FREQ
FREQ/VOLTS
V
DD
1
μ
F
+9V
R
R
STANDARD
TC820
RSTANDARD
RUNKNOWN
ANALOG
COMMON
V
DD
V
+
V
V
+
REF
IN
V
IN
LCD
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