Texas Instruments UA78L05ACPK

The UA78L05ACPK provides a nominal 5 V regulated output for local or on-card power rails. Internal current limiting and thermal shutdown simplify protection against overloads. The AC selection provides tighter 5 V limits than the standard C grade, while the PK suffix identifies the compact SOT-89 surface-mount package.

TI specifies UA78L05ACPK in the three-pin PK package, mechanically identified as SOT-89. The catalog designation TO-243AA is the registered package name used for this product record.

Layout checks

• Use the current TI PK drawing and verify top-view orientation before PCB release.
• Connect adequate copper to the common pin for heat spreading.
• Keep input and output bypass capacitors close to their pins and common.
• Calculate junction temperature from voltage drop, load current, ambient, and board thermal performance.

TI lists 54.7 degrees C/W junction-to-ambient thermal resistance for PK on its standardized test board; actual performance depends strongly on PCB copper.

The PK SOT-89 assignment below follows the TI top-view drawing.

Do not infer pin compatibility from package appearance; verify the exact TI PK drawing when evaluating a substitute.

TI's UA78L05 electrical table uses a 10 V input, 0.33 microfarad input capacitor, 0.1 microfarad output capacitor, and 40 mA load unless otherwise stated.

A replacement must preserve the fixed 5 V output, required current, SOT-89 footprint, OUTPUT/COMMON/INPUT pin order, input-voltage limits, dropout behavior, capacitor guidance, temperature range, and thermal performance. M3 redesigns can have different limits, so qualification must use the data applicable to the delivered marking and order code.

No internal replacement link is asserted without an exact API-confirmed catalog match and engineering review.

Texas Instruments identifies UA78L05ACPK as the 5 V AC-grade UA78L device in the PK SOT-89 package. In TI's nomenclature, 05 denotes the nominal 5 V output, the package designator identifies the mechanical option, and the separate M3 suffix identifies newer process-technology redesigns; that suffix is not present in this exact model.

Confirm the full UA78L05ACPK order code, device marking, PK dimensions, lead finish, packaging label, and lot traceability during incoming inspection. Package appearance alone does not establish authenticity. Electrical sampling should follow the latest TI limits for the applicable legacy-chip version.

Validate input headroom, startup and load transients, capacitor placement, and junction temperature in the final circuit. Regulator dissipation is approximately the input-to-output voltage difference multiplied by load current, with an additional bias-current term, so thermal limits can dominate before the absolute input rating is reached.