ICM7226A_01 Datasheet, PDF (7/19 Pages) Intersil Corporation – 8-Digit, Multi-Function, Frequency Counter/Timer

ICM7226A, ICM7226B
Typical Performance Curves (Continued)
20
f_A (MAX) FREQUENCY UNIT COUNTER,
FREQUENCY RATIO MODES
15
10
f_A (MAX) f_B (MAX) PERIOD
TIME INTERVAL MODES
5
T_A = 25^oC
0
3
4
5
6
V_DD-V_SS (V)
FIGURE 8. f_A(MAX), f_B(MAX) AS A FUNCTION OF SUPPLY
Description
INPUTS A and B
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_A
should be higher than f_B during frequency ratio.
Both inputs are digital inputs with a typical switching thresh-
old of 2.0V at V_DD = 5.0V and input impedance of 250kΩ.
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
COUNTED
TRANSITIONS
Note that the amplitude of the input should not exceed the
device supply (above the V_DD and below the V_SS) by more
than 0.3V, otherwise the device may be damaged.
INPUT A ^4.5V
0.5V
50ns MIN
50ns MIN
t_r = t_f = 10ns
FIGURE 9. WAVEFORM FOR GUARANTEED MINIMUM f_A(MAX)
FUNCTION = FREQUENCY, FREQUENCY RATIO,
UNIT COUNTER
Multiplexed Inputs
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.
INPUT A OR ^4.5V
INPUT B _0.5V
MEASURED
INTERVAL
250ns
MIN
250ns
MIN
t_r = t_f = 10s
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.
FIGURE 10. WAVEFORM FOR GUARANTEED MINIMUM f_B(MAX)
AND f_A(MAX) FOR FUNCTION = PERIOD AND
TIME INTERVAL
7