ICM7226A, ICM7226B
Typical Performance Curves (Continued)
20
15
10
5
f
(MAX) FREQUENCY UNIT COUNTER,
FREQUENCY RATIO MODES
A
f
(MAX) f (MAX) PERIOD
B
A
TIME INTERVAL MODES
o
T
= 25 C
A
0
3
4
5
6
V
-V (V)
DD SS
FIGURE 8. f (MAX), f (MAX) AS A FUNCTION OF SUPPLY
A
B
Description
INPUTS A and B
Both inputs are digital inputs with a typical switching thresh-
old of 2.0V at V = 5.0V and input impedance of 250kΩ.
DD
The signal to be measured is applied to INPUT A in
frequency period, unit counter, frequency ratio and time
interval modes. The other input signal to be measured is
applied to INPUT B in frequency ratio and time interval. f
should be higher than f during frequency ratio.
For optimum performance, the peak-to-peak input signal
should be at least 50% of the supply voltage and centered
about the switching voltage. When these inputs are being
driven from TTL logic, it is desirable to use a pullup resistor.
The circuit counts high to low transitions at both inputs
A
B
Note that the amplitude of the input should not exceed the
COUNTED
TRANSITIONS
device supply (above the V
and below the V ) by more
DD
SS
than 0.3V, otherwise the device may be damaged.
Multiplexed Inputs
50ns MIN
4.5V
0.5V
INPUT A
The FUNCTION, RANGE, CONTROL and EXTERNAL
DECIMAL POINT inputs are time multiplexed to select the
function desired. This is achieved by connecting the appro-
priate Digit driver output to the inputs. The function, range
and control inputs must be stable during the last half of each
digit output, (typically 125µs). The multiplexed inputs are
active high for the common anode lCM7226A and active low
for the common cathode lCM7226B.
t = t = 10ns
50ns MIN
r
f
FIGURE 9. WAVEFORM FOR GUARANTEED MINIMUM f (MAX)
A
FUNCTION = FREQUENCY, FREQUENCY RATIO,
UNIT COUNTER
Noise on the multiplex inputs can cause improper operation.
This is particularly true when the unit counter mode of
operation is selected, since changes in voltage on the digit
drivers can be capacitively coupled through the LED diodes
to the multiplex inputs. For maximum noise immunity, a 10kΩ
resistor should be placed in series with the multiplexed
inputs as shown in the application circuits.
MEASURED
INTERVAL
250ns
MIN
4.5V
0.5V
INPUT A OR
INPUT B
250ns
MIN
t = t = 10s
r
f
FIGURE 10. WAVEFORM FOR GUARANTEED MINIMUM f (MAX)
B
AND f (MAX) FOR FUNCTION = PERIOD AND
A
TIME INTERVAL
9-21
INTERSIL [ Intersil ]
