ICM7226A Просмотр технического описания (PDF) - Harris Semiconductor
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ICM7226A Datasheet PDF : 18 Pages
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ICM7226A, ICM7226B
Typical Applications
The ICM7226 has been designed as a complete stand alone
Universal Counter, or used with prescalers and other cir-
cuitry in a variety of applications. Since INPUT A and INPUT
B are digital inputs, additional circuitry will be required in
many applications, for input buffering, amplification, hystere-
sis, and level shifting to obtain the required digital voltages.
For many applications a FET source follower can be used
for input buffering, and an ECL 10116 line receiver can be
used for amplification and hysteresis to obtain high imped-
ance input, sensitivity and bandwidth. However, cost and
complexity of this circuitry can vary widely, depending upon
the sensitivity and bandwidth required. When TTL prescalers
or input buffers are used, a pull up resistors to VDD should
be used to obtain optimal voltage swing at INPUTS A and B.
If prescalers aren’t required, the ICM7226 can be used to
implement a minimum component Universal Counter as
shown in Figure 20.
For input frequencies up to 40MHz, the circuit shown in Fig-
ure 21 can be used to implement a frequency and period
counter. To obtain the correct value when measuring fre-
quency and period, it is necessary to divide the 10MHz oscil-
lator frequency down to 2.5MHz. In doing this the time
between measurements is lengthened to 800ms and the dis-
play multiplex rate is decreased to 125Hz.
If the input frequency is prescaled by ten, the oscillator fre-
quency can remain at either 10MHz or 1MHz, but the deci-
mal point must be moved. Figure 22 shows use of a ÷10
prescaler in frequency counter mode. Additional logic has
been added to enable the ICM7226 to count the input
directly in period mode for maximum accuracy.
10kΩ
DISPLAY DISPLAY EXT OSC
BLANK TEST ENABLE
A IN
39pF
VDD
VDD
1
B IN
2
10kΩ 3
4
5
D1
6
D8
7
D2
8
D5
D3
9
D4
D2
10
D3
D4
11
12
D5
13
D6
14
D7
15
D8
16
17
RESET
18
19
0.1µF
20
ICM7226B
100kΩ
40
HOLD
39
D4
D8
1N914s
38
37
V+
36
35
10MHz
CRYSTAL
34
V+
33
EXT OSC IN
22MΩ
32
39pF
39pF TYP
31
30 DP
V+
V+
29
g
28
e
27
a
26
d
8
25
VDD
24
b
23
c
D1
4
22
f 100kΩ
21
D2
D3
D1
3
TYPICAL
CRYSTAL
PARAMETERS
CL 22pF
RS 35Ω
6
8
D4
a
b
c
d
e
f
g
DP
D8
D7
D6
D5
D4
D3
D2
D1
D8
FIGURE 20. 10MHz UNIVERSAL COUNTER
13-77
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