Texas Instruments UCC391PW

Overview

UCC391PW from Texas Instruments is a 5-bit programmable BiCMOS precision voltage reference IC that generates an adjustable output from 1.3V to 3.5V in discrete 50 mV or 100 mV steps, with ±1% DC system accuracy over 0°C–70°C, used for VID-code-based CPU core voltage regulation in Pentium II-compatible systems.

For engineers reviewing the UCC391PW datasheet, UCC391PW pinout, UCC391PW application, or UCC391PW equivalent, key selection criteria include DAC resolution (5-bit), output accuracy (±1%), COMMAND pin voltage tolerance (±1.00%), supply current (1.8 mA typ), and compatibility with 5V-only digital control interfaces.

Technical Context

The UCC391PW implements a dual-range DAC architecture where D4 selects between high-range (2.05V–3.5V, 100 mV steps) and low-range (1.3V–2.05V, 50 mV steps); D0–D3 encode the LSB-to-MSB values within each range. All inputs are internally pulled up, and logic '1' is defined by floating the pin while '0' is GND connection.

It integrates trimmed reference and output amplifiers to achieve ±1% total system accuracy across temperature, process, and input voltage variation without external calibration. The COMMAND output drives voltage regulator feedback nodes directly, requiring no external op-amp buffering.

Key Specifications

Pinout & Package

PW package is an 8-pin TSSOP (Thin Shrink Small Outline Package), 3.0 mm × 3.0 mm body, 0.65 mm pitch, lead-free compatible, optimized for high-density PCB layouts in desktop/server CPU VRM modules.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar programmable voltage reference applications.

Compared with TLV431AIDBVR and MAX5023EUA+, the UCC391PW uniquely delivers Pentium II VID protocol compliance in a minimal 8-pin TSSOP, offering system-level ±1% accuracy without external components-making it irreplaceable in legacy x86 VRM retrofits and cost-sensitive desktop motherboard designs.

Availability

UCC391PW is available at Aetrix Electronics and suitable for desktop motherboard design, server VRM development, and legacy x86 embedded systems requiring stable component supply and long-lifecycle support.

Supply support for UCC391PW includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and computing markets.

The UCC391PW belongs to TI's legacy power management reference IC family, specifically engineered for VID-code-based CPU core voltage regulation in second-generation x86 platforms.

FAQ

What is the function of the D4 pin on the UCC391PW?

The D4 pin on the UCC391PW serves as the most significant bit and range-select control for the internal 5-bit DAC. When D4 = 0, the UCC391PW outputs voltages from 1.3V to 2.05V in 50 mV increments; when D4 = 1, it outputs from 2.05V to 3.5V in 100 mV increments. This dual-range architecture enables finer resolution in the lower voltage range required by Pentium II processors. The UCC391PW uses this pin to maintain full VID code compatibility per Table I in its datasheet.

Does the UCC391PW require external passive components to operate?

No, the UCC391PW operates with zero external passive components for basic functionality. Only a 0.1 µF (or larger) ceramic capacitor between VCC and GND is required for supply decoupling. Unlike shunt references or op-amp-based solutions, the UCC391PW integrates trimmed reference and output amplifiers, eliminating the need for external resistors, trim pots, or compensation networks. This simplifies layout and improves reliability in space-constrained VRM designs using the UCC391PW.

What does "COMMAND output disabled" mean when D4–D0 = 11111 on the UCC391PW?

When all five digital inputs (D4–D0) are set high (11111), the UCC391PW places its COMMAND output pin in a high-impedance (Hi-Z) state, effectively disabling the reference signal. This feature supports safe power-down sequencing in CPU VRMs by preventing erroneous voltage commands during reset or shutdown. The UCC391PW enters this mode regardless of VCC level or temperature, and the COMMAND pin remains inactive until a valid VID code (not 11111) is applied. This behavior is explicitly defined in the UCC391PW datasheet.

Is the UCC391PW compatible with modern CPUs or only Pentium II?

The UCC391PW is specifically designed for Intel Pentium II microprocessors and their associated VID code tables (Table I). It is not compatible with later CPU generations (Pentium III, Core, or AMD families) that use different VID protocols, higher bit counts, or SMBus-based communication. While the UCC391PW may electrically function with other 5-bit digital inputs, its output voltage mapping and disable logic match only Pentium II specifications. For newer platforms, engineers should select purpose-built alternatives-not the UCC391PW.

How is the ±1% accuracy of the UCC391PW achieved across temperature and supply variation?

UCC391PW achieves ±1% total system accuracy through factory trimming of both reference and output amplifier offsets prior to packaging-explicitly noted in Note 1 of its electrical characteristics table. This trimming compensates for process variation, and the BiCMOS design ensures stable performance from 0°C to 70°C with 5V ±10% supply. No external calibration or temperature compensation circuitry is needed. The UCC391PW maintains this accuracy without recalibration because all contributing errors (reference drift, amplifier offset, gain error) are simultaneously minimized during wafer-level test and trim.