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參數(shù)資料
| 型號： | TC820CPL |
| 廠商： | TelCom Semiconductor, Inc. |
| 元件分類： | 通用總線功能 |
| 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)換頻率計數(shù)器和邏輯探針轉(zhuǎn)爐 |
| 文件頁數(shù)： | 17/22頁 |
| 文件大?。?/td> | 275K |
| 代理商： | TC820CPL |
3-165
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
1
2
8
TC820
3-3/4 A/D CONVERTER WITH
FREQUENCY COUNTER
AND LOGIC PROBE
Figure 15. Suggested Crystal Oscillator Circuit
5pF
37
38
39
110k
10pF
75pF
TC820
Figure 14. DGND and COM Outputs
+
–
12
μ
A
P
TC820
LOGIC
SECTION
5V
3.2V
N
N
V
DD
V
SS
COM
DGND
Figure 16. R-C Oscillator Circuit
Typical values are R = 10k
and C = 68pF. The resistor
value should be
≥
100k
. For accurate frequency measure-
ment, an R-C oscillator frequency of 40kHz is required.
System Timing
All system timing is derived from the clock oscillator. The
clock oscillator is divided by 2 prior to clocking the A/D
counters. The clock is also divided by 8 to drive the buzzer,
by 240 to generate the LCD backplane frequency, and by
40,000 for the frequency counter time base. A simplified
diagram of the system clock is shown in Figure 17.
Component Value Selection
Auto Zero Capacitor — C
AZ
The value of the auto-zero capacitor (C
AZ
) has some
influence on system noise. A 0.47
μ
F capacitor is recom-
mended; a low dielectric absorption capacitor (Mylar) is
required.
Reference Voltage Capacitor — C
REF
The reference voltage capacitor used to ramp the inte-
grator output voltage back to zero during the reference
integrate cycle is stored on C
REF
. A 0.1
μ
F capacitor is
typical. A good quality, low leakage capacitor (such as
Mylar) should be used.
Integrating Capacitor — C
INT
C
INT
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 (f
OSC
= 40kHz) and V
FS
= 400mV, a 0.22
μ
F
value is suggested. If a different oscillator frequency is used,
C
INT
must be changed in inverse proportion to maintain the
0.3
RC
Clock Oscillator
The TC820 oscillator can be controlled with either a
crystal or with an inexpensive resistor-capacitor combina-
tion. The crystal circuit, shown in Figure 15, is recommended
when high accuracy is required in the frequency counter
mode. The 40kHz crystal is a standard frequency for ultra-
sonic alarms, and will provide a 1-second time base for the
counter or 2.5 analog-to-digital conversions per second.
Consult the crystal manufacturer for detailed applications
information.
Where low cost is important, the R-C circuit of Figure 16
can be used. The frequency of this circuit will be approxi-
mately:
f
OSC
=
TC820
40kHz
38
39
5 pF
10pF
22 M
470k
37
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