ICM7216B_04 Datasheet, PDF (13/18 Pages) Intersil Corporation – 8-Digit, Multi-Function, Frequency Counters/Timers

ICM7216B, ICM7216D
Test Circuit
FUNCTION
GENERATOR
INPUT A
V_DD
V_DD
V_DD
DISPLAY DISPLAY
BLANK TEST _1MHz
EXT
OSC
TEST
FUNCTION
GENERATOR
100pF
HOLD
10kΩ
10kΩ
39pF
39pF
TYP
1
28
INPUT B
2
27
FUNCTION
10K _DP
F
D1
e
P
D8
g
FR
D2
a
TI.
D5
U.C.
O.F.
D4
d
D3
b
c
f
3
26
4
25
5
24
6
23
7
22
ICM7216A
8
21
9
20
10
19
11
18
12
17
13
16
RESET
14
15
6
8
a
b
c
d
e
f
LED
g
OVERFLOW
DP
INDICATOR
D8
D8
D7
D4
D8 D2
D1 D5
22MΩ
10MHz
CRYSTAL
1N914s
EXT
OSC
INPUT
D1
8
D2
D3
D4
D5
V_DD
D6
D7
D8
10kΩ
TYPICAL CRYSTAL SPECS:
F = 10MHz PARALLEL RESONANCE
C_L = 22pF
R_S = <35Ω
RANGE
D1
.01/1
D2
.1/10
4
D3
D4
1/100
10/1K
8
D6
D5
D4
D3
D2
D1
FIGURE 14. TEST CIRCUIT (ICM7216A SHOWN, OTHERS SIMILAR)
Typical Applications
The lCM7216 has been designed for use in a wide range of
Universal and Frequency counters. In many cases, prescalers
will be required to reduce the input frequencies to under 10MHz.
Because INPUT A and INPUT B are digital inputs, additional
circuitry is often required for input buffering, amplification,
hysteresis, and level shifting to obtain a good digital signal.
The lCM7216B can be used as a minimum component
complete Universal Counter as shown in Figure 15. This
circuit can use input frequencies up to 10MHz at INPUT A
and 2MHz at INPUT B. If the signal at INPUT A has a very
low duty cycle it may be necessary to use a 74LS121
monostable multivibrator or similar circuit to stretch the input
pulse width to be able to guarantee that it is at least 50ns in
duration.
To measure frequencies up to 40MHz the circuit of
Figure 16 can be used. To obtain the correct measured
value, it is necessary to divide the oscillator frequency by
four as well as the input frequency. In doing this the time
between measurements is also lengthened to 800ms and
the display multiplex rate is decreased to 125Hz.
If the input frequency is prescaled by ten, then the oscillator
can remain at 10MHz or 1MHz, but the decimal point must
be moved one digit to the right. Figure 17 shows a frequency
counter with a ÷10 prescaler and an lCM7216A. Since there
is no external decimal point control with the lCM7216B, the
decimal point may be controlled externally with additional
drivers as shown in Figure 17. Alternatively, if separate
anodes are available for the decimal points, they can be
wired up to the adjacent digit anodes. Note that there can be
one zero to the left of the decimal point since the internal
leading zero blanking cannot be changed. In Figure 18
additional logic has been added to count the input directly in
period mode for maximum accuracy. In Figures 17 and 18,
INPUT A comes from QC of the prescaler rather than QD to
obtain an input duty cycle of 40%.
13