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DM74LS122 Fiches technique(PDF) 4 Page - National Semiconductor (TI) |
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DM74LS122 Fiches technique(HTML) 4 Page - National Semiconductor (TI) |
4 / 6 page Operating Rules (Continued) The K factor is not a constant but varies with CX See Figure 2 TLF6385 – 3 FIGURE 2 4 The switching diode required for most TTL one-shots when using an electrolytic timing capacitor is not needed for the ’LS122 and should not be used 5 To obtain variable pulse width by remote trimming the following circuit is recommended TLF6385 – 4 Note ‘‘Rremote’’ should be as close to the device pins as possible FIGURE 3 6 The retriggerable pulse width is calculated as shown be- low T e TW a tPLH e 050 c RX c CX a TPLH The retriggered pulse width is equal to the pulse width plus a delay time period (Figure 4) TLF6385 – 5 FIGURE 4 7 Output pulse width variation versus VCC and operation temperatures Figure 5 depicts the relationship between pulse width variation versus VCC and Figure 6 depicts pulse width variation versus temperatures TLF6385 – 6 FIGURE 5 TLF6385 – 7 FIGURE 6 8 Under any operating condition CX and RX must be kept as close to the one-shot device pins as possible to mini- mize stray capacitance to reduce noise pick-up and to reduce I-R and Ldidt voltage developed along their con- necting paths If the lead length from CX to pins (13) 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 non-inductive and low ca- pacitive path is necessary to ensure complete discharge of CX in each cycle of its operation so that the output pulse width will be accurate 9 VCC and ground wiring should conform to good high-fre- quency standards and practices so that switching tran- sients on the VCC and ground return leads do not cause interaction between one-shots A 001 mF to 010 mF by- pass capacitor (disk ceramic or monolithic type) from VCC to ground is necessary on each device 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 NSC one-shot application note AN-366 4 |
Numéro de pièce similaire - DM74LS122 |
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Description similaire - DM74LS122 |
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