Texas Instruments TXS0108EPWR: PCB footprint and gate checks

The Texas Instruments TXS0108EPWR is a 8-bit auto-direction dual-supply voltage translator from Texas Instruments. Its package or board interface is 20-pin TSSOP, and its relevant electrical envelope is VCCA 1.2–3.6 V; VCCB 1.65–5.5 V with VCCA not greater than VCCB. It communicates or connects through eight auto-bidirectional channels with OE. Those fields belong together: substituting a familiar family name while changing package, voltage, sensing port, mount style, current class, or interface behavior can leave a PCB that passes ordinary net checks and still cannot be assembled or function safely.

TXS0108E uses edge accelerators and weak keepers for automatic direction, making bus capacitance and external drive strength critical.

Common uses include mixed-direction GPIO buses and moderate-speed level translation with light loads. Start with the manufacturer drawing and recommended application, then record the exact ordering suffix alongside the KiCad symbol and footprint. This makes the library evidence reviewable when the part is re-sourced months later.

• Place decoupling at every supply domain and use the exact package pinout. Keep the two voltage domains visibly separated in schematic and layout to prevent accidental rail swaps.
• Route direction, enable, and reference pins with the same care as data. Avoid long stubs and connector-adjacent ESD capacitance that exceeds the translator's edge-rate budget.

Decouple both rails, tie OE to VCCA logic, keep traces short, and avoid strong external pull-ups or long capacitive cables outside TI guidance.

• Choose translation architecture for the bus: push-pull, open-drain, auto-direction, or single controlled direction. Auto-bidirectional parts have drive, capacitance, and edge-rate limits that make them poor universal substitutes.
• Sequence or disable the device when either rail can be absent and verify Ioff/back-power behavior. Pull-ups belong to the correct side and must satisfy both rise time and sink current.

Put the support components where their current, thermal, optical, RF, or measurement loops are actually short—not merely where ratsnest lines look tidy. Confirm pin one from the package view used in the datasheet, distinguish top view from mating face or bottom view, and check mask, paste, drill, courtyard, enclosure, and rework access independently. A correct copper pad pattern can still be a bad production footprint when the sensing opening, connector latch, exposed pad, thermal path, or cable volume is wrong.

MakeIRL’s release gate should not stop at “the symbol has the right number of pins.” For this part, a useful gate review combines ERC/DRC with the following package- and function-specific evidence:

1. Check A/B rail voltages and ordering, direction/enable state, decoupling on both rails, Ioff behavior, pull-ups, bus type, capacitance, and expected data rate.
2. Check that open-drain and push-pull signals use an appropriate translator and that no connector or ESD path back-powers an unpowered domain.
3. Check exact manufacturer suffix and package; similarly named translator variants can reverse A/B constraints or change enable polarity.
4. For Texas Instruments TXS0108EPWR, check VCCA≤VCCB, both decouplers, OE reference/pull state, channel capacitance, external pulls, drive type, edge rate, and partial-power behavior.

Then run ERC and DRC, refill zones, and inspect the fabrication and assembly outputs. Cross-probe the exact pads named by any finding, compare the BOM MPN with the footprint and electrical limits above, and verify that a real cable, enclosure, antenna, sensor stimulus, load, or thermal path can be tested on the assembled unit. An exclusion is evidence that someone dismissed a marker; it is not evidence that the underlying condition was resolved.

The most expensive errors are usually plausible: a footprint from a sibling package, a breakout-board voltage copied to the bare IC, a headline current used without thermal analysis, or a connector family selected by pitch alone. For Texas Instruments TXS0108EPWR, review these failure modes explicitly:

• Using TXS0108E for long SPI/display cables or heavily pulled I²C can cause ringing, slow edges, or oscillation.
• Using an auto-direction I²C-style translator on strong push-pull SPI or clocks and getting slow, distorted, or oscillating edges.
• Swapping VCCA and VCCB when only one side is allowed to be the lower-voltage reference.

Sourcing note. Use genuine TXS0108EPWR; similarly named TXB0108 has different architecture and is not an I²C substitute. The approved vendor list should preserve manufacturer, full suffix, package, voltage/range/accuracy grade, lifecycle, and mating or external components. An alternate is real only after its datasheet, land pattern, electrical behavior, firmware assumptions, and assembly process have all been compared—not because a distributor search places it in the same parametric row.