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  • Future-Proofing Your Level Shifter Design with TI's Dual Footprint Packages

    • SCEA136 september   2023 LSF0102 , LSF0108 , SN74AVC2T45 , SN74AXC1T45 , SN74AXC1T45-Q1 , SN74AXC2T45 , SN74AXC4T245 , SN74AXC4T774 , SN74AXC8T245 , TXB0104 , TXB0104-Q1 , TXB0108 , TXS0102 , TXS0104E , TXS0104E-Q1 , TXS0108E , TXU0102 , TXU0102-Q1 , TXU0104 , TXU0104-Q1 , TXU0202 , TXU0202-Q1 , TXU0204 , TXU0204-Q1 , TXU0304 , TXU0304-Q1

       

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Application Brief

Future-Proofing Your Level Shifter Design with TI's Dual Footprint Packages

Introduction

Reducing or eliminating supply shortages within a production flow is essential for many customers. When supply issues arise, customers typically must redesign their boards to accommodate a new package for a given device, forcing customers to push production dates and miss crucial deadlines. However, with TI's expanded small package selections and dual footprint configurations, supply constraints can be reduced. Dual footprint board layout techniques can help mitigate the impact of component shortages by enabling a design to use different package options for a given component.

This application brief covers multiple common package families and provide guidance on how to select a dual footprint.

Dual Footprint Solution using TI's Various Packages

A dual footprint is a footprint which can be used with two or more device packages, with minimal to no routing adjustments, eliminating the need for last minute board redesigns or spins. TI offers a variety of packages for both leaded and non-leaded types. Table 1 shows a few examples of popular packages from TI, while a full list can be found in Find TI Packages. TI's level shifter portfolio contains many of the packages listed below and includes devices under Auto Directional, Direction Controlled and Fixed Direction categories for Industrial, Automotive, and High Reliability applications.

Table 1 Package Family and Designator of Leaded and Non-Leaded Packages
LeadedNon-Leaded
Package FamilyPackage DesignatorPackage FamilyPackage Designator
TSSOPPWUQFNRJW, RSV
VSSOPDGS, DCUVQFNRGY
SSOPDCTWQFNBQA, BQB
SOT-23DBVX2SONDEA, DTQ, DQE
SOT-SC70DCKUSONDRY

With TI's packages being among the industry's smallest, implementing dual footprint layouts for leaded and non-leaded packages is simple given that many of these packages have the same orientation and pinout.

Leaded to Non-Leaded Packages

To create a dual footprint design, the board designer must place the smaller non-leaded package in the center of the larger leaded package, and connect the corresponding pins. This allows either package to be placed on the footprint. Figure 1 shows some examples using TSSOP and QFN packages, while Figure 2 shows some examples using smaller packages like SOT-23 and SOT-SC70 with X2SON and USON. Many level translators use the packages shown in the following examples, and Table 2, Table 3, and Table 4 give the full list of TI devices and the corresponding footprint configurations the devices can support.

GUID-20230822-SS0I-HSC1-6PLZ-8PNVBXCNGJK4-low.svgFigure 1 TSSOP Package Layout With QFNs
GUID-20230825-SS0I-L9JL-PW2B-RFLNQLTGX9GG-low.svgFigure 2 SOT-23, SOT-SC70 Package Layout With X2SON, USON
Table 2 Device Compatibility [Auto Direction]
Dual Footprint CandidatePackage Options
TXS0108E, TXB0108, LSF010820 Pin: PW and RGY
TXS0104E, TXS0104E-Q114 Pin: PW and BQA, PW and RGY
TXB0104, TXB0104-Q114 Pin: PW and RGY
LSF01028 Pin: DCT and DQE, DCU and DQE
Table 3 Device Compatibility [Direction Controlled]
Dual Footprint CandidatePackage Options
SN74AXC8T24524 Pin: PW and RJW
SN74AXC4T245, SN74AXC4T77416 Pin: PW and BQB, PW and RSV
SN74AXC1T45

6 Pin: DBV and DTQ, DBV, and DEA,

6 Pin: DCK and DTQ, DCK, and DEA

SN74AXC1T45-Q16 Pin: DCK and DRY
Table 4 Device Compatibility [Fixed Direction]
Dual Footprint CandidatePackage Options
TXU0304, TXU0304-Q114 Pin: PW and BQA
TXU0204, TXU0204-Q114 Pin: PW and BQA
TXU0104, TXU0104-Q114 Pin: PW and BQA
TXU0202, TXU0202-Q18 Pin: DCU and DTT
TXU0102, TXU0102-Q18 Pin: DCU and DTT

Leaded to Leaded Packages

Creating a dual footprint design depends on the packages used. If using a smaller package like SOT-23-THN, then the package can fit underneath a bigger package like TSSOPs (See PW and DYY example below). If a package cannot fit underneath because of PCB design violations, then the package needs to be moved to the side (See PW and DGS example below). Figure 3 shows an example on how to implement these configurations.

Table 5 and Table 6 gives the full list of devices and the corresponding footprint configurations the devices can support.

GUID-20230829-SS0I-C4SN-SN51-Z1HBD7CCTS6R-low.svgFigure 3 Package Layout of TSSOP, SSOP With VSSOP and SOT-23-THN
Table 5 Device Compatibility [Auto Direction]
Dual Footprint CandidatePackage Options
LSF010820 Pin: PW and DGS
LSF01028 Pin: DCT and DCU
TXS01028 Pin: DCT and DCU
Table 6 Device Compatibility [Direction Controlled]
Dual Footprint CandidatePackage Options
SN74AXC2T458 Pin: DCT and DCU
SN74AVC2T458 Pin: DCT and DCU

Design Consideration

Make sure proper spacing is used when designing a dual footprint layout. Most manufactures follow a 0.1 mm (approximately 4 mil) design rule for spacing between each pad. If such a rule is not followed, there will be insufficient or no space for solder mask to fill between pads of the layout. A lack of solder mask can cause the device to shift, resulting in shorted or floating pins.

Conclusion

Using TI's numerous package options, customers can easily design dual footprint layouts for multiple components which can dramatically reduce the chances of missing delivery deadlines that can result from component supply shortages. Dual footprint layout considerations can be a vital tool for design engineers as they select and design in components that are resilient to supply chain disruptions. Customers can use the previous examples to provide an effective second source and future-proof their design.

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