1-OF-8 DECODER/ DEMULTIPLEXER SN54/74LS138 - ECEE

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SN54/74LS138FUNCTIONAL DESCRIPTIONThe LS138 is a high speed 1-of-8 Decoder/Demultiplexerfabricated with the low power Schottky barrier diode process.The decoder accepts three binary weighted inputs (A0, A1, A2)and when enabled provides eight mutually exclusive activeLOW Outputs (O0–O7). The LS138 features three Enable inputs,two active LOW (E1, E2) and one active HIGH (E3). Alloutputs will be HIGH unless E1 and E2 are LOW and E3 isHIGH. This multiple enable function allows easy parallel expansionof the device to a 1-of-32 (5 lines to 32 lines) decoderwith just four LS138s and one inverter. (See Figure a.)The LS138 can be used as an 8-output demultiplexer byusing one of the active LOW Enable inputs as the data inputand the other Enable inputs as strobes. The Enable inputswhich are not used must be permanently tied to their appropriateactive HIGH or active LOW state.INPUTSTRUTH TABLEOUTPUTSE1 E2 E3 A0 A1 A2 O0 O1 O2 O3 O4 O5 O6 O7H X X X X X H H H H H H H HX H X X X X H H H H H H H HX X L X X X H H H H H H H HL L H L L L L H H H H H H HL L H H L L H L H H H H H HL L H L H L H H L H H H H HL L H H H L H H H L H H H HL L H L L H H H H H L H H HL L H H L H H H H H H L H HL L H L H H H H H H H H L HL L H H H H H H H H H H H LH = HIGH Voltage LevelL = LOW Voltage LevelX = Don’t CareA0A1A2A3LS04A4H123 123 123 123A0 A1 A2EA0 A1 A2EA0 A1 A2 EA0 A1 A2 ELS138O0 O1 O2 O3 O4 O5 O6 O7O0 O1 O2 O3LS138LS138O4 O5 O6 O7 O0 O1 O2 O3 O4 O5 O6 O7LS138O0 O1 O2 O3 O4 O5 O6 O7O0O31Figure aFAST AND LS TTL DATA5-2
SN54/74LS138GUARANTEED OPERATING RANGESSymbol Parameter Min Typ Max UnitVCC Supply Voltage 5474TA Operating Ambient Temperature Range 5474IOH Output Current — High 54, 74 –0.4 mAIOL Output Current — Low 5474DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE (unless otherwise specified)LimitsSymbol Parameter Min Typ Max Unit Test ConditionsiVIH Input HIGH Voltage 2.0 VVILInput LOW Voltage54 0.774 0.8V4.54.75–5505.05.025255.55.25125704.08.0Guaranteed Input HIGH Voltage forAll InputsGuaranteed Input LOW Voltage forAll InputsVIK Input Clamp Diode Voltage –0.65 –1.5 V VCC = MIN, IIN = – 18 mAV°CmAVOHOutput HIGH VoltageVOLOutput LOW Voltage54 25 2.5 35 3.5 V VCC = MIN, IOH = MAX, VIN = VIH74 2.7 3.5 Vor VIL per Truth Table54, 74 0.25 0.4 V IOL = 4.0 mA VCC = VCC MIN,VIN =VIL or VIH74 0.35 0.5 V IOL = 8.0 mA per Truth TableIIHInput HIGH Current20 µA VCC = MAX, VIN = 2.7 V0.1 mA VCC = MAX, VIN = 7.0 VIIL Input LOW Current –0.4 mA VCC = MAX, VIN = 0.4 VIOS Short Circuit Current (Note 1) –20 –100 mA VCC = MAXICC Power Supply Current 10 mA VCC = MAXNote 1: Not more than one output should be shorted at a time, nor for more than 1 second.AC CHARACTERISTICS (TA = 25°C)SymbolParametertPLHtPHLtPLHtPHLtPLHtPHLtPLHtPHLPropagation DelayAddress to OutputPropagation DelayAddress to OutputPropagation Delay E1 or E2Enable to OutputPropagation Delay E3Enable to OutputLevels ofLimitsDelay Min Typ Max Unit Test Conditionsi2233223313271826122117252041273918322638nsnsnsnsVCC = 5.0 VCL = 15 pFAC WAVEFORMSVIN1.3 V1.3 VVIN1.3 V1.3 VVOUTtPHL1.3 VtPLH1.3 VVOUTtPHL1.3 VtPLH1.3 VFigure 1 Figure 2FAST AND LS TTL DATA5-3
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1-OF-8 DECODER/ DEMULTIPLEXER SN54/74LS138 - ECEE

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