74lvcc4245a应用手册

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Application ReportSCEA021A - September 2002Texas Instruments Voltage-Level-Translation DevicesNadira Sultana and Chris CockrillABSTRACTIn electronic systems design, there is a need to provide an interface between different voltagelevels. Texas Instruments offers four split-rail bus transceivers with dual voltage-supplyinputs. These transceivers allow translation between 3.3-V LVTTL/LVCMOS and 5-V CMOS,2.5-V CMOS and 5-V CMOS, and 2.5-V CMOS and 3.3-V LVTTL/LVCMOS. These devicesare the SN74LVCC3245A, SN74LVC4245A, SN74LVCC4245A, and application report discusses the use of these devices to achieve successfulvoltage rd Linear & LogicContentsIntroduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Device Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Dual-Supply Bus Transceivers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Configurable-Output Bus Transceivers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Features and Benefits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Power-Up Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Glossary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12List of FiguresSwitching Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Comparison of Switching Standards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3SN74LVC4245A Pinout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4SN74ALVC164245 Pinout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4SN74LVCC3245A Pinout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5SN74LVCC4245A Pinout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6SN74LVC4245A ICCA and ICCB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8SN74LVCC4245A ICCA and ICCB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9SN74LVCC3245A ICCA and ICCB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10SN74ALVC164245 ICCA and ICCB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

SCEA021AList of Tables123Possible Voltage-Translation Combinations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Features and Benefits of Level-Translation Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Power-Up Sequence for Level-Translation Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7IntroductionThe simultaneous use of different supply-voltage levels has led to the need for voltagetranslation. In some cases, the logic devices are compatible with the different voltage levels,while in other cases they are not. To have switching compatibility between a driver and areceiver, the output of the driver must be compliant with the input of the receiver. VOL

of thedriver should be equal to, or less than, VIL of the receiver. To establish a high-level signal at thereceiver, VOH of the driver should be greater than, or equal to, VIH (see Figure 1).VCCVOHDriverReceiverVOHNoise MarginVIHVIHVtVtVtVILVILNoise MarginVOLVOLGNDSwitching StandardsGNDGNDDriver/Receiver CompatibilityFigure ing StandardsWhile translating from 3.3-V LVTTL/LVCMOS to 5-V CMOS, VIH for 5-V CMOS is 3.5 V, whereasVOH for 3.3-V LVTTL is 2.4 V (see Figure 2).2Texas Instruments Voltage-Level-Translation Devices

SCEA021A5 VVCC4.44 VVOH3.5 VVIHVt3.3 V2.4 V2.0 VVCCVOHVIHVt2.5 V2.3 V1.7 V1.2 V0.7 V0.2 V0 VVCCVOHVIHVtVILVOLGND2.5 V1.5 VVIL1.5 V0.8 V0.5 V0 VVOLGND0.4 V0 VVILVOLGND5-V CMOS5 V Rail to Rail3.3-V LVTTL/LVCMOS2.5-V CMOSFigure ison of Switching StandardsThus, standard 3.3-V devices cannot achieve this type of translation. Texas Instruments split-raildevices have two separate voltage supplies, one at each port. These devices allow fortranslation between 3.3-V LVTTL/LVCMOS to 5-V CMOS, 2.5-V CMOS to 5-V CMOS, 2.5-VCMOS to 3.3-V LVTTL/LVCMOS, and vice DescriptionDual-Supply Bus TransceiversThe SN74LVC4245A (see Figure 3) is an 8-bit (octal) noninverting bus transceiver that has twopower-supply rails. The A port is set at 5 V, while the B port is set at 3.3 V. This allows fortranslation from a 3.3-V to a 5-V environment, and vice versa. The data is transmitted from theA bus to the B bus, or the B bus to the A bus, depending on the logic level at thedirection-control (DIR) input. If the buses must be isolated, the device can be disabled using theoutput-enable (OE) input. Texas Instruments Voltage-Level-Translation Devices3

SCEA021ADB, DW, OR PW PACKAGE(TOP VIEW)(5 V) VCCADIRA1A2A3A4A5A6A7A8GNDGND2413VCCB (3.3 V)VCCB (3.3 V)OEB1B2B3B4B5B6B7

B8GNDFigure 74LVC4245A PinoutThe SN74ALVC164245 (see Figure 4) is a 16-bit (dual-octal) noninverting bus transceiver. Itsoperation is similar to the SN74LVC4245A. The only functional difference is that, in the case ofthe SN74ALVC164245, VCCA is set to 3.3 V, and VCCB is set to 5 V, the opposite of theSN74LVC4245A OR DL PACKAGE(TOP VIEW)1DIR1B11B2GND1B31B4(5 V) VCCB1B51B6GND1B71B82B12B2GND2B32B4(5 V) VCCB2B52B6GND2B72B82DIR544434241443332313OE1A11A2GND1A31A4VCCA (3.3 V)1A51A6GND1A71A82A12A2GND2A32A4VCCA (3.3 V)2A52A6GND2A72A82OEFigure 74ALVC164245 Pinout4Texas Instruments Voltage-Level-Translation Devices

SCEA021AVCCA is the control side for these two devices. Therefore, the control inputs, DIR (direction) andOE (output enable), should be driven by VCCA CMOS logic. For the SN74LVC4245A, DIR andOE should be driven by 5-V CMOS logic. For the SN74ALVC16425, DIR and OE should bedriven by 3.3-V CMOS urable-Output Bus TransceiversThe SN74LVCC3245A and SN74LVCC4245A are 8-bit (octal) dual-supply bus transceivers withconfigurable output voltages. This means the data on the B bus follow the value of VCCB. In theSN74LVCC3245A, VCCA operates between 2.3 V and 3.6 V, while VCCB accepts voltages from3 V to 5.5 V. This device allows translation from 3.3 V to 5 V, 2.5 V to 3.3 V, or 2.5 V to 5 V, andvice versa. The SN74LVCC4245A operates slightly differently. VCCA accepts a 5-V supply level,and VCCB accepts voltages from 3 V to 5 V. Therefore, this device translates only between 3.3 Vand 5 V. SN74LVCC3245A and SN74LVCC4245A are shown in Figure 5 and Figure 6,, DW, OR PW PACKAGE(TOP VIEW)VCCADIRA1A2A3A4A5A6A7A8GNDGND2413VCCBNCOEB1B2B3B4B5B6B7

B8GNDNC – No internal connectionFigure 74LVCC3245A Pinout Texas Instruments Voltage-Level-Translation Devices5

SCEA021ADB, DW, OR PW PACKAGE(TOP VIEW)VCCADIRA1A2A3A4A5A6A7A8GNDGND2413VCCBNCOEB1B2B3B4B5B6B7

B8GNDNC – No internal connectionFigure 74LVCC4245A PinoutVCCA

is the control side for these two devices. Therefore, the control inputs should be driven byVCCA CMOS logic. For the SN74LVCC4245A, DIR and OE should be driven by 5-V CMOS logic,and for the SN74LVCC3245A, DIR and OE should be driven by 3.3-V CMOS 1 details possible voltage-translation le Voltage-Translation CombinationsDEVICESUPPLY VOLTAGEPOSSIBLEVOLTAGE-TRANSLATION COMBINATIONS(TO/FROM)A PORTSN74LVC4245ASN74ALVC164245A4.5 V ≤ VCCA ≤ 5.5 V2.7 V ≤ VCCB ≤ 3.6 V2.7 V ≤ VCCA ≤ 3.6 V4.5 V ≤ VCCB ≤ 5.5 V2.3 V ≤ VCCA ≤ 3.6 V3 V ≤ VCCB ≤ 5.5 V4.5 V ≤ VCCA ≤ 5.5 V2.7 V ≤ VCCB ≤ 5.5 V5-V CMOS3.3-V LVTTL/LVCMOS2.5-V CMOSSN74LVCC3245A2.5-V CMOS3.3-V LVTTL/LVCMOS3.3-V LVTTL/LVCMOSSN74LVCC4245A5-V CMOS5-V CMOSB PORT3.3-V LVTTL/LVCMOS5-V CMOS3.3-V LVTTL/LVCMOS5-V CMOS5-V CMOS3.3-V LVTTL/LVCMOS3.3-V LVTTL/LVCMOS5-V CMOS6Texas Instruments Voltage-Level-Translation Devices

SCEA021AFeatures and BenefitsTable 2 summarizes the features and corresponding benefits of these level-translation es and Benefits of Level-Translation DevicesFEATURESTwo separate power-supply rails:VCCB at the B port takes 3.3 V,VCCA at the A port takes 5 separate power-supply rails:VCCB at the B port takes 5 V,VCCA at the A port takes 3.3 separate power-supply rails:VCCB at the B port takes 5 V,VCCA at the A port takes 2.5 V to 3.3 enable can be used todisable the SSN74LVC4245ASN74LVCC4245ABENEFITSAllows 3.3-V to 5-V level translation, and vice versaSN74ALVC164245Allows 3.3-V to 5-V level translation, and vice versaAllow 3.3-V to 5-V, 2.5-V to 3.3-V, and 2.5-V to 5-V level translations, andvice versaSN74LVCC3245ASN74LVC4245ASN74LVCC4245ASN74ALVC164245SN74LVCC3245ASN74LVCC4245ASN74LVCC3245ABuses are isolated effectively without false signaling, when real-time applications, such as PCMCIA, need full-rail data signalsto maximize interface capability, which can be accomplished by tying VCCBof the device to the PCMCIA card voltage supply.B port is configurable, which means Bport is designed to track -Up ConsiderationsTI level-translation devices offer an opportunity for successful mixed-voltage signal design. Aproper power-up sequence always should be followed to avoid excessive supply current, buscontention, oscillations, or other anomalies caused by improperly biased device pins. Take theseprecautions to guard against such power-up t ground before any supply voltage is , power up the control side of the device (VCCA for all four of these devices). OE to VCCA with a pullup resistor so that it ramps with ing on the direction of the data path, DIR can be high or low. If DIR high is needed(A data to B bus), ramp it with VCCA. Otherwise, keep DIR 3 gives a brief summary about the power-up sequence of the -Up Sequence for Level-Translation DevicesDEVICESN74LVC4245ASN74LVCC4245AVCCA5 V(power up first)5 V(power up first)3.3 V(power up first)3.3 V(power up first)VCCB3.3 V(power up second)3.3 V(power up second)5 V(power up second)5 V(power up second)OETied to VCCA with a pullup resistorTied to VCCA with a pullup resistorTied to VCCA with a pullup resistorTied to VCCA with a pullup resistorSN74LVCC3245ASN74ALVC164245 Texas Instruments Voltage-Level-Translation Devices7

SCEA021AThe power-up sequence was tested in the laboratory for all four of these devices. Figures 7–10show the ICCA and ICCB for the SN74LVC4245A, SN74LVCC4245A, SN74LVCC3245A, andSN74ALVC164245 devices during power up. VCCA was powered up first, then VCCB

was was tied to VCCA with a 1-kΩ pullup resistor. Figures 7(a)–10(a) show the ICC with DIR high,and Figures 7(b)–10(b) show the ICC with DIR low. If the device is powered up in the correctmanner, it draws a reasonable amount of current and ensures the proper functioning of thedevice.4535ICC–

mA2515ICCAICCB00.511.522.5Voltagea) SN74LVC4245A POWER UP WITH DIR HIGH33.544.5550–54535ICC–

mA251550–500.511.522.5Voltageb) SN74LVC4245A POWER UP WITH DIR LOW33.544.55ICCAICCBFigure 74LVC4245A ICCA and ICCB8Texas Instruments Voltage-Level-Translation Devices

SCEA021A4535Am25

–CCI155I0CCAICCB–500.511.522.533.544.55Voltagea) SN74LVCC4245A POWER UP WITH DIR HIGH453525CC1550ICCAICCB–500.511.522.533.544.55Voltageb) SN74LVCC4245A POWER UP WITH DIR LOWFigure 74LVCC4245A ICCA and ICCB Texas Instruments Voltage-Level-Translation Devices9I–

mA

SCEA021A4535ICC–

mA251550–500.511.522.5Voltagea) SN74LVCC3245A POWER UP WITH DIR HIGH33.544.55ICCAICCB4535ICC–

mA251550–500.511.522.5Voltageb) SN74LVCC3245A POWER UP WITH DIR LOW33.544.55ICCAICCBFigure 74LVCC3245A ICCA and ICCB10Texas Instruments Voltage-Level-Translation Devices

SCEA021A4535Am25

–CCI15ICCA50ICCB–5012345Voltagea) SN74ALVC164245 POWER UP WITH DIR HIGH4535Am25

–CCI15ICCA50ICCB–5012345Voltageb) SN74ALVC164245 POWER UP WITH DIR LOWFigure 74ALVC164245 ICCA and ICCB Texas Instruments Voltage-Level-Translation Devices11

SCEA021AConclusionTexas Instruments offers four split-rail devices, SN74LVC4245A, SN74LVCC4245A,SN74LVCC3245A, and SN74ALVC164245 that can be used for 3.3-V to 5-V, 2.5-V to 3.3-V, and2.5-V to 5-V translation, and vice versa. These devices are available in octal and Widebusconfigurations, which give the opportunity for designers to choose the optimal part for theirapplications. These devices have strict power-sequencing requirements that prevent excessivecurrent flow or possible damage to the devices. These stringent requirements sometimes aredifficult to meet from a system timing standpoint and may offer little flexibility for partial systempower down or other advanced power-saving design techniques. Careful selection of thesedevices and adoption of an appropriate power-up sequencing technique can lead to a successfulmixed-voltage ryCMOSComplementary metal-oxide semiconductorLVCMOSLow-voltage CMOSLVTTLVCCVIHVILVOHVOLVtLow-voltage TTL (3.3-V power supply and interface levels)Supply voltageHigh-level input voltageLow-level input voltageHigh-level output voltageLow-level output voltageThreshold voltageWidebus is a trademark of Texas Instruments.12Texas Instruments Voltage-Level-Translation Devices

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