ICM7226A Ver la hoja de datos (PDF) - Harris Semiconductor

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Fabricante

ICM7226A

8-Digit Multi-Function Frequency Counter/Timers

Harris Semiconductor 

ICM7226A, ICM7226B

Typical Performance Curves (Continued)

20

fA (MAX) FREQUENCY UNIT COUNTER,

FREQUENCY RATIO MODES

15

10

fA (MAX) fB (MAX) PERIOD

TIME INTERVAL MODES

5

TA = +25oC

0

3

4

5

6

VDD-VSS (V)

FIGURE 8. fA(MAX), fB(MAX) AS A FUNCTION OF SUPPLY

Description

INPUTS A and B

The signal to be measured is applied to INPUT A in fre-

quency 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. fA should be

higher than fB during frequency ratio.

COUNTED

TRANSITIONS

Both inputs are digital inputs with a typical switching thresh-

old of 2.0V at VDD = 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

INPUT A 4.5V

0.5V

50ns MIN

50ns MIN

tR = tF = 10ns

Note that the amplitude of the input should not exceed the

device supply (above the VDD and below the VSS) by more

than 0.3V, otherwise the device may be damaged.

Multiplexed Inputs

FIGURE 9. WAVEFORM FOR GUARANTEED MINIMUM fA(MAX)

FUNCTION = FREQUENCY, FREQUENCY RATIO,

UNIT COUNTER

INPUT A OR 4.5V

INPUT B 0.5V

MEASURED

INTERVAL

250ns

MIN

250ns

MIN

tR = tF = 10s

FIGURE 10. WAVEFORM FOR GUARANTEED MINIMUM fB(MAX)

AND fA(MAX) FOR FUNCTION = PERIOD AND TIME

INTERVAL

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.

Noise on the multiplex inputs can cause improper operation.

This is particularly true when the unit counter mode of oper-

ation is selected, since changes in voltage on the digit driv-

ers 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.

13-70

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