74HC138 Datasheet, PDF (2/7 Pages) NXP Semiconductors – 3-to-8 line decoder/demultiplexer; inverting

Philips Semiconductors
3-to-8 line decoder/demultiplexer; inverting
Product specification
74HC/HCT138
FEATURES
• Demultiplexing capability
• Multiple input enable for easy expansion
• Ideal for memory chip select decoding
• Active LOW mutually exclusive outputs
• Output capability: standard
• I_CC category: MSI
GENERAL DESCRIPTION
The 74HC/HCT138 are high-speed Si-gate CMOS devices
and are pin compatible with low power Schottky TTL
(LSTTL). They are specified in compliance with JEDEC
standard no. 7A.
The 74HC/HCT138 decoders accept three binary
weighted address inputs (A₀, A₁, A₂) and when enabled,
provide 8 mutually exclusive active LOW outputs (Y₀ to
Y₇).
The “138” features three enable inputs: two active LOW
(E₁ and E₂) and one active HIGH (E₃). Every output will be
HIGH unless E₁ and E₂ are LOW and E₃ is HIGH.
This multiple enable function allows easy parallel
expansion 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.
QUICK REFERENCE DATA
GND = 0 V; T_amb = 25 °C; t_r = t_f = 6 ns
SYMBOL
t_PHL/ t_PLH
t_PHL/ t_PLH
C_I
C_PD
PARAMETER
propagation delay
A_n to Y_n
E₃ to Y_n
E_n to Y_n
input capacitance
power dissipation capacitance per package
CONDITIONS
TYPICAL
HC
HCT
C_L = 15 pF; V_CC = 5 V
12
17
14
19
notes 1 and 2
3.5
3.5
67
67
Notes
1. C_PD is used to determine the dynamic power dissipation (P_D in µW):
P_D = C_PD × V_CC2 × f_i + ∑ (C_L × V_CC2 × f_o) where:
f_i = input frequency in MHz
f_o = output frequency in MHz
∑ (C_L × V_CC2 × f_o) = 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 V
UNIT
ns
ns
pF
pF
ORDERING INFORMATION
See “74HC/HCT/HCU/HCMOS Logic Package Information”.
September 1993
2