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5-197 fast and ls ttl data retriggerable monostable multivibrators these dc triggered multivibrators feature pulse width control by three meth - ods. the basic pulse width is programmed by selection of external resistance and capacitance values. the ls122 has an internal timing resistor that allows the circuits to be used with only an external capacitor . once triggered, the ba - sic pulse width may be extended by retriggering the gated low-level-active (a) or high-level-active (b) inputs, or be reduced by use of the overriding clear. ? overriding clear terminates output pulse ? compensated for v cc and temperature variations ? dc triggered from active-high or active-low gated logic inputs ? retriggerable for very long output pulses, up to 100% duty cycle ? internal timing resistors on ls122 sn54 / 74ls122 (top view) (see notes 1 thru 4) sn54 / 74ls123 (top view) (see notes 1 thru 4) notes: 1. an external timing capacitor may be connected between c ext and r ext /c ext (positive). 2. t o use the internal timing resistor of the ls122, connect r int to v cc . 3. for improved pulse width accuracy connect an external resistor between r ext /c ext and v cc with r int open-circuited. 4. to obtain variable pulse widths, connect an external variable resistance between r int /c ext and v cc .
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" sn54/74ls122 sn54/74ls123 retriggerable monostable multivibrators low power schottky j suffix ceramic case 620-09 n suffix plastic case 648-08 16 1 16 1 ordering information sn54lsxxxj ceramic sn74lsxxxn plastic sn74lsxxxd soic 16 1 d suffix soic case 751b-03 j suffix ceramic case 632-08 n suffix plastic case 646-06 14 1 14 1 14 1 d suffix soic case 751a-02
5-198 fast and ls ttl data sn54/74ls122 ? sn54/74ls123 ls122 functional table inputs outputs clear a1 a2 b1 b2 q q l x x x x l h x h h x x l h x x x l x l h x x x x l l h h l x h h l x h h x l h h x l h h h h h h h h h h h h l x h h x l h h ls123 functional table inputs outputs clear a b q q l x x l h x h x l h x x l l h h l h h l h typical application data the output pulse t w is a function of the external compo - nents, c ext and r ext or c ext and r int on the ls122. for values of c ext 1000 pf , the output pulse at v cc = 5.0 v and v rc = 5.0 v (see figures 1, 2, and 3) is given by t w = k r ext c ext where k is nominally 0.45 if c ext is on pf and r ext is in k w then t w is in nanoseconds. the c ext terminal of the ls122 and ls123 is an internal connection to ground, however for the best system perfor - mance c ext should be hard-wired to ground. care should be taken to keep r ext and c ext as close to the monostable as possible with a minimum amount of inductance between the r ext /c ext junction and the r ext /c ext pin. good groundplane and adequate bypassing should be designed into the system for optimum performance to insure that no false triggering occurs. it should be noted that the c ext pin is internally connected to ground on the ls122 and ls123, but not on the ls221. therefore, if c ext is hard-wired externally to ground, substitu - tion of a ls221 onto a ls123 socket will cause the ls221 to become non-functional. the switching diode is not needed for electrolytic capaci - tance application and should not be used on the ls122 and ls123. to find the value of k for c ext 1000 pf, refer to figure 4. variations on v cc or v rc can cause the value of k to change, as can the temperature of the ls123, ls122. figures 5 and 6 show the behavior of the circuit shown in figures 1 and 2 if separate power supplies are used for v cc and v rc . if v cc is tied to v rc , figure 7 shows how k will vary with v cc and temperature. remember, the changes in r ext and c ext with temperature are not calculated and included in the graph. as long as c ext 1000 pf and 5k r ext 260k (sn74ls122 / 123) or 5k r ext 160 k (sn54ls122 / 123), the change in k with respect to r ext is negligible. if c ext 1000 pf the graph shown on figure 8 can be used to determine the output pulse width. figure 9 shows how k will change for c ext 1000 pf if v cc and v rc are connected to the same power supply . the pulse width t w in nanoseconds is approximated by t w = 6 + 0.05 c ext (pf) + 0.45 r ext (k w ) c ext + 11.6 r ext in order to trim the output pulse width, it is necessary to include a variable resistor between v cc and the r ext /c ext pin or between v cc and the r ext pin of the ls122. figure 10, 1 1, and 12 show how this can be done. r ext remote should be kept as close to the monostable as possible. retriggering of the part, as shown in figure 3, must not occur before c ext is discharged or the retrigger pulse will not have any ef fect. the discharge time of c ext in nanoseconds is guaranteed to be less than 0.22 c ext (pf) and is typically 0.05 c ext (pf). for the smallest possible deviation in output pulse widths from various devices, it is suggested that c ext be kept 1000 pf.
5-199 fast and ls ttl data sn54/74ls122 ? sn54/74ls123 guaranteed operating ranges symbol parameter min typ max unit v cc supply voltage 54 74 4.5 4.75 5.0 5.0 5.5 5.25 v t a operating ambient temperature range 54 74 55 0 25 25 125 70 c i oh output current e high 54, 74 0.4 ma i ol output current e low 54 74 4.0 8.0 ma r ext external timing resistance 54 74 5.0 5.0 180 260 k w c ext external capacitance 54, 74 no restriction r ext / c ext wiring capacitance at r ext / c ext terminal 54, 74 50 pf waveforms extending pulse width overriding the output pulse

5-200 fast and ls ttl data sn54/74ls122 ? sn54/74ls123 dc characteristics over operating temperature range (unless otherwise specified) symbol parameter limits unit test conditions symbol parameter min typ max unit test conditions v ih input high voltage 2.0 v guaranteed input high voltage for all inputs v il input low voltage 54 0.7 v guaranteed input low voltage for all inputs v il input low voltage 74 0.8 v guaranteed input low voltage for all inputs v ik input clamp diode voltage 0.65 1.5 v v cc = min, i in = 18 ma v oh output high voltage 54 2.5 3.5 v v cc = min, i oh = max, v in = v ih or v il per truth table v oh output high voltage 74 2.7 3.5 v v cc = min, i oh = max, v in = v ih or v il per truth table v ol output low voltage 54, 74 0.25 0.4 v i ol = 4.0 ma v cc = v cc min, v in = v il or v ih per truth table v ol output low voltage 74 0.35 0.5 v i ol = 8.0 ma v in = v il or v ih per truth table i ih input high current 20 m a v cc = max, v in = 2.7 v i ih input high current 0.1 ma v cc = max, v in = 7.0 v i il input low current 0.4 ma v cc = max, v in = 0.4 v i os short circuit current (note 1) 20 100 ma v cc = max i cc power supply current ls122 11 ma v cc = max i cc power supply current ls123 20 ma v cc = max note 1: not more than one output should be shorted at a time, nor for more than 1 second. ac characteristics (t a = 25 c, v cc = 5.0 v) symbol parameter limits unit test conditions symbol parameter min typ max unit test conditions t plh t phl propagation delay, a to q propagation delay, a to q 23 33 ns c ext = 0 c l = 15 pf r ext = 5.0 k w r l = 2.0 k w t plh t phl propagation delay, a to q propagation delay, a to q 32 45 ns c ext = 0 c l = 15 pf r ext = 5.0 k w r l = 2.0 k w t plh t phl propagation delay, b to q propagation delay, b to q 23 44 ns c ext = 0 c l = 15 pf r ext = 5.0 k w r l = 2.0 k w t plh t phl propagation delay, b to q propagation delay, b to q 34 56 ns r ext = 5.0 k w r l = 2.0 k w t plh t phl propagation delay, clear to q propagation delay, clear to q 28 45 ns r ext = 5.0 k w r l = 2.0 k w t plh t phl propagation delay, clear to q propagation delay, clear to q 20 27 ns t w min a or b to q 116 200 ns c ext = 1000 pf, r ext = 10 k w , c l = 15 pf, r l = 2.0 k w t w q a to b to q 4.0 4.5 5.0 m s c ext = 1000 pf, r ext = 10 k w , c l = 15 pf, r l = 2.0 k w ac setup requirements (t a = 25 c, v cc = 5.0 v) symbol parameter limits unit test conditions symbol parameter min typ max unit test conditions t w pulse width 40 ns
5-201 fast and ls ttl data sn54/74ls122 ? sn54/74ls123 figure 1 figure 2 figure 3 figure 4 &$ m #%$ &$ &$ &$ &$ &$ m #%$ w &$ &$ &$ 1/2 ls123 ls122 &$ w !" !" !" #%$ $ &$

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5-202 fast and ls ttl data sn54/74ls122 ? sn54/74ls123 figure 8 figure 5. k versus v cc figure 6. k versus v rc figure 7. k versus v cc and v rc k
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5-203 fast and ls ttl data sn54/74ls122 ? sn54/74ls123 figure 9 figure 10. ls123 remote trimming circuit

5-204 fast and ls ttl data sn54/74ls122 ? sn54/74ls123 figure 11. ls122 remote trimming circuit without r ext figure 12. ls122 remote trimming circuit with r int

5-205 fast and ls ttl data

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5-206 fast and ls ttl data motorola reserves the right to make changes without further notice to any products herein. motorola makes no warranty , representation or guarantee regarding the suitability of its products for any particular purpose, nor does motorola assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability , including without limitation consequential or incidental damages. at ypicalo parameters can and do vary in dif ferent applications. all operating parameters, including at ypicalso must be validated for each customer application by customer ' s technical experts. motorola does not convey any license under its patent rights nor the rights of others. motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body , or other applications intended to support or sustain life, or for any other application in which the failure of the motorola product could create a situation where personal injury or death may occur . should buyer purchase or use motorola products for any such unintended or unauthorized application, buyer shall indemnify and hold motorola and its of ficers, employees, subsidiaries, af filiates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly , any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that motorola was negligent regarding the design or manufacture of the part. motorola and are registered trademarks of motorola, inc. motorola, inc. is an equal opportunity/af firmative action employer . literature distribution centers: usa: motorola literature distribution; p .o. box 20912; phoenix, arizona 85036. europe: motorola ltd.; european literature centre; 88 t anners drive, blakelands, milton keynes, mk14 5bp , england. jap an: nippon motorola ltd.; 4-32-1, nishi-gotanda, shinagawa-ku, t okyo 141, japan. asia p acific: motorola semiconductors h.k. ltd.; silicon harbour center , no. 2 dai king street, t ai po industrial estate, t ai po, n.t., hong kong. ?

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