Texas Instruments UCC3946PWTR

Overview

UCC3946PWTR from Texas Instruments is a microprocessor supervisor IC with integrated watchdog timer, programmable reset threshold (1.235 V ±2%), programmable reset period (160–260 ms with 64 nF), and programmable watchdog period (1.12–2.08 s with 64 nF), operating from 2 V to 5.5 V supply and supporting industrial temperature range (0°C to 70°C). It ensures reliable power-on reset and glitch-immune supervision in embedded control systems.

For engineers reviewing the UCC3946PWTR datasheet, UCC3946PWTR pinout, UCC3946PWTR application, or UCC3946PWTR equivalent, key selection criteria include its 1V valid reset assertion, 18 µA max supply current, independent RES/WDO outputs, RTH-based threshold programming, and TSSOP-8 package compatibility with space-constrained PCB layouts.

Technical Context

The UCC3946PWTR implements dual independent timing blocks: a precision 400 nA current source charges external capacitors at RP (reset period) and WP (watchdog period), enabling user-defined delays via CRP and CWP. Its internal 1.235 V reference compares against voltage divider output at RTH to determine reset assertion.

Reset logic incorporates hysteresis (15 mV) and glitch rejection-only voltage dips exceeding both amplitude and duration thresholds (per Figure 1) trigger RES. Watchdog operation disables during active reset, and WDO asserts low upon WDI timeout, supporting NMI-driven fault recovery.

Key Specifications

Pinout & Package

UCC3946PWTR is housed in an 8-pin TSSOP (PW) package, 3.0 mm × 4.4 mm, 0.65 mm pitch, lead-free and RoHS-compliant.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microprocessor supervision applications.

Compared with MAX6816EUK+T and TPS3808G33DBVR, the UCC3946PWTR uniquely supports full programmability of both reset and watchdog thresholds via external resistors and capacitors-enabling multi-rail monitoring, custom timing, and legacy system compatibility without redesign.

Availability

UCC3946PWTR is available at Aetrix Electronics and suitable for industrial PLC controllers, smart meter power management, medical infusion pump MCUs, and automotive body control modules requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for UCC3946PWTR 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, embedded processing, and connectivity solutions for industrial, automotive, and personal electronics markets.

The UCC3946PWTR belongs to TI's microprocessor supervisor product line, engineered specifically for high-reliability embedded systems requiring precise, field-configurable reset and watchdog supervision under variable supply and temperature conditions.

FAQ

What is the minimum supply voltage at which UCC3946PWTR guarantees a valid reset output?

The UCC3946PWTR guarantees a valid reset output (RES asserted low) down to 1 V supply voltage, as specified in the Electrical Characteristics table under "Minimum VDD (Note 1)". This ensures deterministic reset behavior during severe brownout or backup power transitions, even before the internal reference fully stabilizes. The 1 V specification is validated across the full industrial temperature range (0°C to 70°C) and applies regardless of external RTH divider configuration. UCC3946PWTR maintains this capability while drawing ≤18 µA total supply current.

How do I configure the reset threshold voltage for UCC3946PWTR?

The reset threshold voltage for UCC3946PWTR is configured using two external resistors (R1 and R2) forming a voltage divider connected to the RTH pin. The formula is V_RESET = 1.235 V × (R1 + R2)/R2. For example, selecting R1 = 1 MΩ and R2 = 330 kΩ yields ~5.0 V threshold. Resistor values in the megaohm range minimize current draw while maintaining accuracy. UCC3946PWTR's internal 1.235 V reference has ±2% tolerance, so final threshold accuracy depends on both resistor tolerance and reference stability. Layout best practice requires short traces to RTH to avoid noise coupling.

Can UCC3946PWTR supervise a voltage rail other than VDD?

Yes, UCC3946PWTR can supervise any voltage rail-not just VDD-by connecting that rail through an appropriate resistor divider to the RTH pin. The device compares the divided voltage against its internal 1.235 V reference, making it suitable for monitoring 1.8 V, 2.5 V, 3.3 V, 5 V, or higher rails. The only constraints are that the RTH node voltage must remain within absolute maximum ratings (≤10 V), and the divider must provide sufficient current to overcome input leakage (<5 nA). UCC3946PWTR's wide 2 V to 5.5 V VDD operating range further supports mixed-rail supervision architectures.

What happens to the watchdog function when UCC3946PWTR is in reset?

When UCC3946PWTR is in reset (i.e., RES is asserted low), the watchdog function is automatically disabled-the WDI input is ignored, and WDO remains high regardless of WDI state. This prevents spurious watchdog timeouts during power-up or brownout recovery, ensuring the microprocessor completes initialization before watchdog supervision begins. Once RES deasserts (goes high), the watchdog timer restarts and begins monitoring WDI toggles. If RES is reasserted later (e.g., due to a voltage dip), WDO immediately goes high and the watchdog period resets. This behavior is hardwired in UCC3946PWTR's internal logic and requires no external control.

Is UCC3946PWTR pin-compatible with UCC2946PWTR or UCC1946PWTR?

UCC3946PWTR shares identical pinout and package (TSSOP-8) with UCC2946PWTR and UCC1946PWTR, but they differ in temperature grade and electrical specifications: UCC3946PWTR is rated for 0°C to 70°C, UCC2946PWTR for –40°C to 95°C, and UCC1946PWTR for –55°C to 125°C. While pinout and basic functionality match, key parameters vary-e.g., UCC3946PWTR operates down to 2 V (vs. 2.1 V for UCC2946/UCC1946), and its reset threshold min/max is 1.210 V/1.260 V (vs. 1.170 V/1.260 V for others). Therefore, direct substitution requires validation of voltage and temperature requirements in the target application.