Texas Instruments UCC3946PW

Overview

UCC3946PW 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), and programmable watchdog period (1.12–2.08 s). It operates from 2 V to 5.5 V, draws ≤18 µA supply current, and asserts valid reset down to VDD = 1 V - used in embedded systems requiring reliable power-on and fault recovery.

For engineers reviewing the UCC3946PW datasheet, UCC3946PW pinout, UCC3946PW application, or UCC3946PW equivalent, key selection criteria include its 2% accurate reset threshold, glitch-immune RTH sensing, dual external capacitor programming (RP/WP), and TSSOP-8 package compatibility with space-constrained industrial controllers and battery-powered microcontrollers.

Technical Context

The UCC3946PW implements two independent timing circuits: a precision 400 nA current source charges CRP to set the reset period (TRP = 3.125 × CRP), and a separate 25 nA source charges CWP for watchdog timeout (TWP = 25 × CWP). Both thresholds reference an internal 1.235 V bandgap.

Its reset logic includes hysteresis (15 mV) and glitch rejection via overdrive-delay response (e.g., 120 µs delay for 100 mV overdrive), while the watchdog disables during reset and reinitializes upon RES assertion - ensuring deterministic fault-handling sequencing in safety-critical firmware.

Key Specifications

Pinout & Package

UCC3946PW is housed in an 8-pin TSSOP (PW) package - 3.0 mm × 4.4 mm, 0.65 mm pitch - optimized for high-density PCB layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS3808G33DBVR and MAX6816EUT+T, the UCC3946PW uniquely combines fully programmable reset and watchdog timing with sub-2% threshold accuracy and 1 V reset validity - making it irreplaceable in applications requiring adaptive supervision under varying supply conditions.

Availability

UCC3946PW is available at Aetrix Electronics and suitable for industrial PLC controllers, medical infusion pumps, automotive body control modules, and smart energy meters requiring stable component supply and long-term lifecycle support.

Supply support for UCC3946PW 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 personal electronics markets.

The UCC3946PW belongs to TI's legacy microprocessor supervisor product line, designed specifically for robust power-monitoring and fault-recovery in resource-constrained embedded systems where programmability and low-voltage operation are essential.

FAQ

What is the minimum supply voltage at which UCC3946PW guarantees valid reset assertion?

The UCC3946PW guarantees functional reset assertion down to VDD = 1 V, as specified in the Electrical Characteristics table (Note 1). This ensures reliable operation during deep brownout or battery-sag events. The RES output remains valid and capable of driving a load even at this low voltage, enabling fail-safe behavior in energy-limited systems where other supervisors may cease functioning.

How does the UCC3946PW reject supply glitches without causing false resets?

The UCC3946PW rejects glitches using a voltage-overdrive vs. delay response defined in Figure 1: transients less than 100 mV in amplitude or shorter than 120 µs are ignored at the RTH pin. This built-in filtering prevents false resets from EMI, switching noise, or load-dump spikes. The behavior is inherent to the analog comparator design and requires no external components - a key differentiator from basic reset ICs.

Can UCC3946PW monitor a voltage other than VDD for reset purposes?

Yes, the UCC3946PW can monitor any voltage ≥1.235 V via the RTH pin using an external resistor divider. The reset threshold is set by V_RESET = 1.235 × (R1 + R2)/R2, allowing supervision of auxiliary rails (e.g., 1.8 V core, 2.5 V I/O) independently of VDD. This flexibility is explicitly documented in the "Programming the Reset Voltage" section and supported by the high-impedance RTH input (leakage ≤5 nA).

What happens to the watchdog function when UCC3946PW is in reset?

When UCC3946PW asserts RES (during power-up or brownout), the watchdog function is automatically disabled - WDI toggles are ignored, and WDO remains high. Upon RES deassertion, the watchdog timer reinitializes and begins counting from zero. This prevents spurious timeouts during unstable power conditions and ensures the watchdog only monitors healthy firmware execution.

Is UCC3946PW pin-compatible with UCC2946PW or UCC1946PW?

Yes, UCC3946PW shares identical pinout and package (TSSOP-8) with UCC2946PW and UCC1946PW, as confirmed by the shared Connection Diagram and Pin Descriptions. However, temperature ranges differ: UCC3946PW is rated for 0°C to 70°C, while UCC2946PW covers –40°C to 95°C and UCC1946PW –55°C to 125°C - thermal validation is required for cross-substitution.