Texas Instruments UC2903Q

Overview

UC2903Q from Texas Instruments is a quad supply and line monitor IC designed for industrial power system supervision. It monitors up to four independent voltage rails-including one negative rail via internal inverter-with programmable under- and over-voltage thresholds centered on a 2.5-V precision reference, 30-mA open-collector fault outputs, and –40°C to +85°C operating range.

For engineers reviewing the UC2903Q datasheet, UC2903Q pinout, UC2903Q application, or UC2903Q equivalent, this page delivers verified technical context, exact pin functions for PLCC-20 package, real-world timing and threshold behavior, and validated alternative options for multi-rail monitoring in telecom power supplies, industrial PLCs, and redundant DC systems.

Technical Context

The UC2903Q implements four independent sense comparators with thresholds derived from a 2.5-V reference and scaled by window-adjust voltage (Pin 4), delivering proportional hysteresis (10–30 mV/V) and ±0.25-V adjustable offset. Its dedicated Sense 4 inverter enables direct negative-supply monitoring without external components.

Three open-collector outputs-UV FAULT, OV FAULT, and POWER OK-respond with user-programmable delays (20–50 ms/µF) to respective fault conditions; the POWER OK output is active-low and asserts only when all monitored rails and the line/switcher sense input are within valid windows.

Key Specifications

Pinout & Package

UC2903Q is housed in a 20-pin PLCC (FN) package with gull-wing leads, RoHS-compliant CuSn finish, and JEDEC Level-2 moisture sensitivity rating.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad supply monitoring applications.

Compared with UC3903Q and UC2903DW, the UC2903Q uniquely combines industrial temperature range, PLCC-20 mechanical compatibility with legacy military designs, and explicit Sense 4 inverter control-making it the sole option for drop-in replacement in fielded UC1903L-based systems requiring –40°C operation.

Availability

UC2903Q is available at Aetrix Electronics and suitable for telecom power shelves, industrial PLCs, redundant server PSUs, and medical imaging systems requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for UC2903Q 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 leader specializing in analog, embedded processing, and power management technologies with over 50 years of innovation in industrial and automotive electronics.

The UC2903Q belongs to TI's UC1903 family of precision supply monitors-designed specifically for high-reliability power supervision in mission-critical industrial, telecom, and defense systems where deterministic fault response and long-term parametric stability are mandatory.

FAQ

What is the operating temperature range specified for the UC2903Q?

The UC2903Q is rated for operation from –40°C to +85°C, qualifying it for industrial-grade applications including factory automation, outdoor telecom equipment, and transportation electronics. This range is confirmed in TI's official packaging addendum and electrical characteristics table, distinguishing it from the commercial-grade UC3903Q (0°C to +70°C) and military-grade UC1903L (–55°C to +125°C). The UC2903Q maintains full functionality-including reference accuracy, fault threshold stability, and open-collector sink current-across this entire span.

How does the UC2903Q handle negative voltage monitoring?

The UC2903Q monitors negative supplies using its dedicated Sense 4 inverter: when the SENSE 4 INVERT INPUT pin is held high, the internal emitter-follower inverter actively inverts the signal applied to SENSE 4, allowing direct connection to a negative rail (e.g., –12 V) through a resistive divider. The inverter's output feeds the comparator stage referenced to the 2.5-V internal reference. This eliminates external op-amps or level-shifters. The UC2903Q datasheet Figure 6 and Section "Sensing a Negative Voltage Level" confirm this architecture is fully characterized and production-tested.

Can the UC2903Q monitor more than four voltage rails?

No-the UC2903Q has exactly four dedicated sense inputs (SENSE 1 through SENSE 4), with SENSE 4 configurable for either positive or negative rail monitoring via its inverter. There are no additional sense channels, multiplexing capability, or internal ADC to extend monitoring beyond four rails. However, the general-purpose op-amp can be externally configured to condition signals from additional rails before feeding them into one of the existing sense inputs-though this requires external components and sacrifices op-amp flexibility. The block diagram and pin description in the UC2903Q datasheet explicitly limit sensing to these four inputs.

What is the purpose of the WINDOW ADJUST pin on the UC2903Q?

The WINDOW ADJUST pin (Pin 4) sets both the magnitude and hysteresis of the fault window for all four sense inputs. Applying a voltage between 0.5 V and 2.5 V scales the offset from the 2.5-V reference: for example, 1.0 V at Pin 4 yields ±0.25-V offsets (±10% of 2.5 V), resulting in a total 0.5-V window centered at 2.5 V. Hysteresis is fixed at 8% of that window width. This single-pin adjustment avoids discrete resistor networks and enables dynamic window tuning-confirmed in the "Setting a Fault Window" section and Figure 2 of the UC2903Q datasheet.

Does the UC2903Q provide power-good sequencing control?

The UC2903Q does not provide active sequencing control (e.g., timed enable/disable signals), but its POWER OK output serves as a hardware-level sequencing enabler: it asserts low only when all four sense inputs, the line/switcher sense input, and the +VIN supply are simultaneously within valid windows. Designers use this single open-collector signal to gate downstream regulators or release microcontroller reset lines-ensuring all rails are stable before system startup. The UC2903Q datasheet Section "Start Latch and Supply Under-Voltage Sense Allow Predictable Power-Up" confirms this behavior is intrinsic to the POWER OK logic architecture.