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descríption
Programmable Output Pulse Width
With RJnt. . ,35nsTyp
Wrth Rext/Cext.,. 40 ns to 28 Seconds
Internal Compensation for Virtual
Temperature Independence
Jitter-Free Operatíon up to 90%
Duty Cycle
Inhíbit Capabílity
FUNCT1ONTA8LE
INPUTS OUTPUTS
A1 A2 B Q Q
L X H L H
X L H L H
X X L L H
H H X L H
H 1 H J~L ~1_T
1
I
H
1
H
H
_TL
_n_
~LT
T_T
L X t J~L ~1_T
X L t J1. 1_T
ivmboli, « " 3-8.
TYPES SN54121, SN54L121. SN74121, SN74L121
MONOSTABLE MULTM'BRATORS
W1TH SCHMITT-TRIGGER INPUTS
SN54121 ... J-OR WPACKAGE
SN54L121 ... J OH TPACKAGE
SN7«121.SN74l_121 ...J OR N PACKAGE
VCc NC NC C.Kt C,,, Rjnl . NC
NC—No intofrul connection
sitl»» logic: Se« function table
•NOTES: 1. An «xt»rn*l cmofchor m»y t» conn*ci*d brt—wn
CBKt (pdtJílv.) «na R.xt/C.jn.
2. To uw tn* Iniarn*! Tlmlng mlnor, conn»ci R|nt
to Vcc. For lmprov«j pulw wlrtrh «(Xuricv *ntí
rvcMitaolIlty, conn>ct »n •xt^riu) m'itar b»tv-»«>o
n,»:l/C.XT «nd Vcc wltn R|n( op>n~clicui1*a.
These multívibrators feature dual negaiíve-transition-triogered inputs and a single positive-transition-tnggered inpui
which can be used as an inhibít input. Complementary cxitput pulses are provided.
Pulse triggering occurs at a particular voltage leve! and ís not dírectly related to The Transition time of The input pulse.
Schmin-trigger input circuiíry (TTL hysTeresís) for tile B input allows jiner-free triggering from inpuc witii transition
rates as slow as 1 volt/second, províding the circuít with an excellent noíse immunity of typically 1.2 volts. A high
immunity to VQC noíse of typically 1.5 volts is also provided by mternal latching circuitry,
Once fired, rhe outputs are independen! af further transiTÍons of the ¡nputs aod are a functíon only of the TÍmíng \. Input pulses may be of any dur
40 nanoseconds to 28 seconds by choosing appropriaTe Timing components. With no exTernal límíng components ¡
(i.e., R¡nt connecred lo VQC. C^x^ and Rext/^ext °Pen), an output pulse of Typically 30 or 35 nanoseconds ís achieved
which may be used as a d-c tríggered reset signa). Ourput rise and fall times are TTL compatible and independent of ¡
pulse length.
Pulse wídth stabílity is achieved through internal compensatíon and Ís virtually independent of VCQ and temperaTure.
In mosT applicatíons, pulse sTabiliiy wíll only be limiied by ihe accuracy of exTernal timíng components.
Jíner-free operatíon is maíntaíned over the ful! temperature and VQC ranges for more than s¡x decades of tíming
capacítance (10 pF to lO^F) and more than one decade of timing resistance (2 kO to 30 kfl for ihe
SN54121/SN54L121 and 2 k£7 to 40 tcíl for the SN74121/SN74U21). Throughout these ranges, pulse wídth ts
defíned by the relationship tw(out) - CeXiRTÍn2 =0.7 C,;XIRj. In círcuits where pulse cutoff Ís not criiical, n'ming
capachance up to 1000 pF and liming resistance as low as 1.4 kH may be used. Also, The range of ¡iner-free OUTPUT
pulse widThs Is extended íf VCG ís ne'd ío 5 volt5 and free*a!'' temperarure is 25°C. DUTY cycles as high as 90% are
•achieved when usíng máximum recommended Ry. Hígher duty cycles are available if a certain amount of pulse-wídth
JÍTter ís allowed.
TEXAS INSTRUMENTS
INCORPORATED