ICM7226A_01 Datasheet, PDF (14/19 Pages) Intersil Corporation – 8-Digit, Multi-Function, Frequency Counter/Timer

ICM7226A, ICM7226B
Typical Applications
The ICM7226 has been designed as a complete stand alone
Universal Counter, or used with prescalers and other circuitry
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, hysteresis, and
level shifting to obtain the required digital voltages. For many
applications a FET source follower can be used for input buff-
ering, and an ECL 10116 line receiver can be used for amplifi-
cation and hysteresis to obtain high impedance 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 V_DD 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
Figure 21 can be used to implement a frequency and
period counter. To obtain the correct value when measuring
frequency and period, it is necessary to divide the 10MHz
oscillator 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
frequency can remain at either 10MHz or 1MHz, but the
decimal 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
V_DD
V_DD
B IN
D1
D8
D2
D5
D4
D3
RESET
0.1µF
1
2
10kΩ ³
4
5
6
7
8
D3
9
D2
10
D4
11
12
D5
13
D6
14
D7
15
D8
16
17
18
19
20
ICM7226B
100kΩ
40
HOLD
D4
D8
39
1N914s
38
37
V+
36
35
34
V+
10MHz
CRYSTAL
33
EXT OSC IN
22MΩ
32
39pF
39pF (TYP)
31
30 DP
V+
V+
29
g
28
e
27
a
26
d
8
25
V_DD
24
b
23
c
D1
4
22
f _100kΩ
21
D2
D3
D1
3
TYPICAL
CRYSTAL
PARAMETERS
C_L 22pF
R_S 35Ω
6
8
D4
a
b
c
d
e
f
g
DP
D8
D7
D6
D5
D4
D3
D2
D1 _D8
OVERFLOW
FIGURE 20. 10MHz UNIVERSAL COUNTER
14