The number of frequency ranges can be increased by using a rotary switch SA1 with more than four positions, and by adding some additional RC components. The device can measure sinusoidal wave and square wave input signals. The pulse width produced by the monostable multivibrator depends on the values of capacitors C C5 and trimming potentiometers R The pulse frequency depends on the input frequency. The pulse voltage is proportional to the input frequency, through the diode VD5 this voltage charges the capacitor C1.
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Features, Applications The is a monostable multivibrator featuring both positive and negative edge triggering with complementary outputs. An internal 2k timing resistor is provided for design convenience minimizing component count and layout problems. A high immunity to VCC noise of typically 1. To obtain optimum and trouble free operation please read operating rules and one-shot application notes carefully and observe recommendations.
Once triggered the output pulse width is independent of further transitions of the inputs and is function of the timing components. There are three trigger inputs from the device, two negative edge-triggering A inputs, one positive edge Schmitt-triggering B input. An external resistor RX or the internal resistor 2 k and an external capacitor CX are required for proper operation. The value of CX may vary from 0 to any necessary value.
For small time constants use high-quality mica, glass, polypropylene, polycarbonate, or polystyrene capacitors. For large time constants use solid tantalum or special aluminum capacitors. If the timing capacitors have leakages approaching or if stray capacitance from either terminal to ground is greater than 50 pF the timing equations may not represent the pulse width the device generates. The pulse width is essentially determined by external timing components RX and CX.
For pF see Figure 1 design curves tW as function of timing components value. Figure 4 depicts pulse width variation versus ambient temperature. The "K" coefficient is not a constant, but varies as a function of the timing capacitor CX. Figure 5 details this characteristic.
If the lead length from CX to pins 10 and 11 is greater than 3 cm, for example, the output pulse width might be quite different from values predicted from the appropriate equations. A noninductive and low capacitive path is necessary to ensure complete discharge CX in each cycle of its operation so that the output pulse width will be accurate.
VCC and ground wiring should conform to good highfrequency standards and practices so that switching transients on the VCC and ground return leads do not cause interaction between one-shots. Furthermore, the bypass capacitor should be located as close to the VCC-pin as space permits. For further detailed device characteristics and output performance please refer to the one-shot application note, AN The device should not be operated at these limits.
The parametric values defined in the Electrical Characteristics tables are not guaranteed at the absolute maximum ratings. The Recommended Operating Conditions table will define the conditions for actual device operation.
Note 4: Not more than one output should be shorted at a time.
PDF 74121 Datasheet ( Hoja de datos )
Reproduction of information in TI data datasneet or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. TI has discontinued the production of the device. Datasheets search archive of electronic components datasheets Product device recommended for new datashfet. Information published by TI regarding third-party products or services does not constitute a license from TI to use such products or services or a warranty or endorsement thereof. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. Not recommended for new designs.
PDF 74121 Datasheet ( Hoja de datos )