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74HC238P

3-to-8 line decoder/demultiplexer

Philips Electronics 

Philips Semiconductors

3-to-8 line decoder/demultiplexer

Product specification

74HC/HCT238

FEATURES

• Demultiplexing capability

• Multiple input enable for easy expansion

• Ideal for memory chip select decoding

• Active HIGH mutually exclusive outputs

• Output capability: standard

• ICC category: MSI

GENERAL DESCRIPTION

The 74HC/HCT238 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/HCT238 decoders accept three binary

weighted address inputs (A0, A1, A2) and when enabled,

provide 8 mutually exclusive active HIGH outputs

(Y0 to Y7).

The “238” features three enable inputs: two active LOW

(E1 and E2) and one active HIGH (E3). Every output will be

LOW unless E1 and E2 are LOW and E3 is HIGH.

This multiple enable function allows easy parallel

expansion of the “238” to a 1-of-32 (5 lines to 32 lines)

decoder with just four “238” ICs and one inverter.

The “238” 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 “238” is identical to the “138” but has non-inverting

outputs.

QUICK REFERENCE DATA

GND = 0 V; Tamb = 25 °C; tr = tf = 6 ns

SYMBOL PARAMETER

CONDITIONS

tPHL/ tPLH

CI

CPD

propagation delay

An to Yn

E3 to Yn

En to Yn

input capacitance

power dissipation capacitance per package

CL = 15 pF; VCC = 5 V

notes 1 and 2

Notes

1. CPD is used to determine the dynamic power dissipation (PD in µW):

PD = CPD × VCC2 × fi + ∑ (CL × VCC2 × fo) where:

fi = input frequency in MHz

fo = output frequency in MHz

∑ (CL × VCC2 × fo) = sum of outputs

CL = output load capacitance in pF

VCC = supply voltage in V

2. For HC the condition is VI = GND to VCC

For HCT the condition is VI = GND to VCC − 1.5 V

TYPICAL

HC

HCT

14

18

16

20

17

21

3.5

3.5

72

76

UNIT

ns

ns

ns

pF

pF

ORDERING INFORMATION

See “74HC/HCT/HCU/HCMOS Logic Package Information”.

December 1990

2

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