ICM7216B_04 Datasheet, PDF (11/18 Pages) Intersil Corporation – 8-Digit, Multi-Function, Frequency Counters/Timers

ICM7216B, ICM7216D
V_DD
SIGNAL A
SIGNAL B
V_DD
2
INPUT A
2
INPUT B
N.O.
PRIME
1
150K
1
1
10K
1
100K
1N914
0.1µF
10nF
V_SS
V_SS
V_SS
DEVICE
1
2
TYPE
CD4049B Inverting Buffer
CD4070B Exclusive - OR
FIGURE 10. PRIMING CIRCUIT, SIGNALS A AND B BOTH
HIGH OR LOW
Following the priming procedure (when in single event or 1
cycle range) the device is ready to measure one (only)
event.
When timing repetitive signals, it is not necessary to “prime”
the lCM7216B as the first alternating signal states
automatically prime the device. See Figure 1.
During any time interval measurement cycle, the lCM7216B
require 200ms following B going low to update all internal
logic. A new measurement cycle will not take place until
completion of this internal update time.
Oscillator Considerations
The oscillator is a high gain CMOS inverter. An external
resistor of 10MΩ to 22MΩ should be connected between the
OSCillator INPUT and OUTPUT to provide biasing. The
oscillator is designed to work with a parallel resonant 10MHz
quartz crystal with a static capacitance of 22pF and a series
resistance of less than 35Ω.
For a specific crystal and load capacitance, the required gM
can be calculated as follows:
g_M
=
ω²
C_IN
C_OUT

R_{S } 1
+
C_{-----O---}
C_L
2
where C_L
=



-_C--^C--_I--_N-^I--^N--+--^C---_C--^O---_O-^U---_U-^T---_T--_{}
CO = Crystal Static Capacitance
RS = Crystal Series Resistance
CIN = Input Capacitance
COUT = Output Capacitance
ω = 2πf
The required gM should not exceed 50% of the gM specified
for the lCM7216 to insure reliable startup. The OSCillator
11
INPUT and OUTPUT pins each contribute about 5pF to CIN
and COUT. For maximum stability of frequency, CIN and
COUT should be approximately twice the specified crystal
static capacitance.
In cases where non decade prescalers are used it may be
desirable to use a crystal which is neither 10MHz or 1MHz.
In that case both the multiplex rate and time between
measurements will be different. The multiplex rate is
f_MUX
=
---^f--^O-----^S----^C----
2 × 10⁴
for 10MHz mode and
f_MUX
=
---^f--^O-----^S----^C----
2 × 10³
for
the 1MHz mode. The time between measurements is
2_-----×_-----1_---0_----⁶_{- in the 10MHz mode and} 2_-----×_-----1_---0_----⁵_{- in the 1MHz mode.}
f_OSC
f_OSC
The crystal and oscillator components should be located as
close to the chip as practical to minimize pickup from other
signals. Coupling from the EXTERNAL OSClLLATOR
INPUT to the OSClLLATOR OUTPUT or INPUT can cause
undesirable shifts in oscillator frequency.
Display Considerations
The display is multiplexed at a 500Hz rate with a digit time of
244µs. An interdigit blanking time of 6µs is used to prevent
display ghosting (faint display of data from previous digit
superimposed on the next digit). Leading zero blanking is
provided, which blanks the left hand zeroes after decimal
point or any non zero digits. Digits to the right of the decimal
point are always displayed. The leading zero blanking will be
disabled when the Main Counter overflows.
The lCM7216B and lCM7216D are designed to drive
common cathode displays at peak current of 15mA/segment
using displays with VF = 1.8V at 15mA. Resistors can be
added in series with the segment drivers to limit the display
current in very efficient displays, if required. The Typical
Performance Curves show the digit and segment currents as
a function of output voltage.
To get additional brightness out of the displays, VDD may be
increased up to 6.0V. However, care should be taken to see
that maximum power and current ratings are not exceeded.
The segment and digit outputs in lCM7216s are not directly
compatible with either TTL or CMOS logic when driving
LEDs. Therefore, level shifting with discrete transistors may
be required to use these outputs as logic signals.
Accuracy
In a Universal Counter crystal drift and quantization effects
cause errors. In frequency, period and time interval
modes, a signal derived from the oscillator is used in either
the Reference Counter or Main Counter. Therefore, in
these modes an error in the oscillator frequency will cause
an identical error in the measurement. For instance, an
oscillator temperature coefficient of ²_----⁰_{---P----P----M---} will cause a
measurement error of ²_----⁰_{---P----P----M---}
o_C
o_C