ICM7226A, ICM7226B
Typical Applications
The ICM7226 has been designed as a complete stand alone For input frequencies up to 40MHz, the circuit shown in
Universal Counter, or used with prescalers and other circuitry Figure 21 can be used to implement a frequency and
in a variety of applications. Since INPUT A and INPUT B are period counter. To obtain the correct value when measuring
digital inputs, additional circuitry will be required in many frequency and period, it is necessary to divide the 10MHz
applications, for input buffering, amplification, hysteresis, and oscillator frequency down to 2.5MHz. In doing this the time
level shifting to obtain the required digital voltages. For many between measurements is lengthened to 800ms and the dis-
applications a FET source follower can be used for input buff- play multiplex rate is decreased to 125Hz.
ering, and an ECL 10116 line receiver can be used for amplifi-
If the input frequency is prescaled by ten, the oscillator
cation and hysteresis to obtain high impedance input,
frequency can remain at either 10MHz or 1MHz, but the
sensitivity and bandwidth. However, cost and complexity of
decimal point must be moved. Figure 22 shows use of a ÷10
this circuitry can vary widely, depending upon the sensitivity
prescaler in frequency counter mode. Additional logic has
and bandwidth required. When TTL prescalers or input buffers
been added to enable the ICM7226 to count the input
are used, a pull up resistors to V
DD
should be used to obtain
directly in period mode for maximum accuracy.
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.
DISPLAY DISPLAY EXT OSC
10kΩ
BLANK
TEST
ENABLE
39pF
V
DD
V
DD
100kΩ
A IN
B IN
D4
D8
1N914s
D1
HOLD
1
2
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
3
10kΩ
V+
4
3
5
10MHz
CRYSTAL
D1
6
D8
V+
EXT OSC IN
7
D2
D5
D4
22MΩ
8
39pF
39pF (TYP)
9
D3
D2
D4
TYPICAL
CRYSTAL
10
11
12
13
14
15
16
17
18
19
20
ICM7226B
V+
V+
PARAMETERS
D3
DP
g
C
R
22pF
35Ω
L
S
e
D5
a
D6
D7
D8
8
4
d
V
DD
b
c
RESET
D1
f
100kΩ
D2
D3
0.1µF
D4
8
a
b
c
d
e
f
6
g
DP
D8
D7
D6
D5
D4
D3
D2
D1
D8
FIGURE 20. 10MHz UNIVERSAL COUNTER
9-28
INTERSIL [ Intersil ]
