general description the 74HC138 are high-speed si-gate cmos devices and are pin compatible with low power schottky ttl(lsttl). t hey are specified in compliance with jedec standard no. 7a. the 74HC138 decoders accept three binary weighted address inputs (a 0 , a 1 , a 2 ) and when enabled,provide 8 mutually exclusive active low outputs (y 0 toy 7 ). the ?138? features three enable inputs: two active low(e 1 and e 2 ) and one active high (e 3 ). every output will be high unless e 1 and e 2 are low and e 3 is high.this multiple enable function allows easy parallelexpansion of the ?138? to a 1-of-32 (5 lines to 32 lines )decoder with just four ?138? ics and one inverter. the ?138? can be used as an eight output demultiplexer by using one of the active low enable inputs as the data input and the remaining enable inputs as strobes. unused enable inputs must be permanently tied to their appropriate active high or low state. the ?138? is identical to the ?238? but has inverting outputs. features ? demultiplexing capability ? multiple input enable for easy expansion ? ideal for memory chip select decoding ? active low mutually exclusive outputs ? output capability: standard ? icc category: msi pin description pin no. symbol name and function 1, 2, 3 4, 5 6 8 7 9-15 16 a 0 to a 2 e 1 , e 2 e 3 gnd y 0 to y 7 v cc address inputs enable inputs (active low) enable input (active high) ground (0 v) outputs (active low) positive supply voltage 1 of 6 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 74HC138
quick reference data gnd = 0 v; tamb = 25 c; tr = tf = 6 ns symbol parameter conditions typical unit hc t phl / t plh t phl / t plh propagation delay a n to y n e 3 to y n e n to y n c l = 15 pf; v cc = 5 v 12 14 ns ns c i input capacitance 3.5 pf c pd power dissipation capacitance per package notes 1 and 2 67 pf notes 1. c pd is used to determine the dynamic power dissipation (p d in w): p d = c pd v cc 2 fi+ (cl v cc 2 fo) where: f i = input frequency in mhz f o = output frequency in mhz (c l v cc 2 fo) = sum of outputs c l = output load capacitance in pf v cc = supply voltage in v 2. for hc the condition is v i = gnd to v cc for hct the condition is v i = gnd to v cc ? 1.5 2 of 6 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 74HC138
function table inputs outputs e1 e2 e3 a0 a1 a2 y0 y1 y2 y3 y4 y5 y6 y7 h x x x h x x x l x x x x x x x x x h h h h h h h h h h h h h h h h h h h h h h h h l l l l l l l l l l l l l l l l h h h h h h h h l h l h l h l h l l h h l l h h l l l l h h h h l h h h h h h h h l h h h h h h h h l h h h h h h h h l h h h h h h h h l h h h h h h h h l h h h h h h h h l h h h h h h h h l notes 1. h = high voltage level l = low voltage level x = don?t care 3 of 6 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 74HC138
4 of 6 ac characteristics gnd = 0 v; tr = t f = 6 ns; c l = 50 pf symbol parameter t amb (c unit test conditions v cc (v) waveforms +25 ? 40 to +85 ? 40 to 125 min. typ ma x. min max. min max t phl / t plh propagation delay a n to y n 41 15 12 150 30 26 190 38 33 225 45 38 na 2.0 4.5 6.0 fig.6 t phl / t plh propagation de e 3 to y n 47 17 14 150 30 26 190 38 33 225 45 38 na 2.0 4.5 6.0 fig.6 t phl / t plh propagation delay e n to y n 47 17 14 150 30 26 190 38 33 225 45 38 na 2.0 4.5 6.0 fig.7 t thl / t tlh output transition time 19 7 6 75 15 13 95 19 16 110 22 19 na 2.0 4.5 6.0 figs 6 and 7 ac waveforms (1) hc : v m = 50%; v i = gnd to v cc . fig.6 waveforms showing the address input (a n ) and enable input (e 3 ) to output (y n ) propagation delays and the output transition times (1) hc : v m = 50%; v i = gnd to v cc . hct: v m = 1.3 v; v i = gnd to 3 v. fig.7 waveforms showing the enable input (e n ) to output (y n ) propagation delays and the output transition times. 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 74HC138
package description sop16 package outline dimensions 5 of 6 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 74HC138
dip16 package outline dimensions 6 of 6 4008-318-123 sales@twtysemi.com http://www.twtysemi.com product specification 74HC138
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