Texas Instruments UCC3946N

Overview

UCC3946N 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 consuming ≤18 µA quiescent current. It asserts RES down to VDD = 1 V and supports glitch-immune power-on reset in embedded control systems.

For engineers reviewing the UCC3946N datasheet, UCC3946N pinout, UCC3946N application, or UCC3946N equivalent, key selection criteria include its 2% accurate reset threshold, 18 µA max IDD, dual programmability (RP and WP pins), guaranteed RES validity at 1 V, and compatibility with SOIC-8 (N package) for industrial microcontroller supervision.

Technical Context

The UCC3946N implements independent reset and watchdog circuits sharing a precision 1.235 V internal reference and 400 nA current sources for RP and WP timing capacitors. Its reset section features hysteresis (15 mV) and glitch rejection based on overdrive voltage vs. delay (Fig. 1), while the watchdog logic monitors WDI edge transitions and disables during active reset.

It uses external R1/R2 resistors to scale the 1.235 V reference for custom reset thresholds and supports manual reset via parallel switch across R2. The RES and WDO outputs are open-drain, enabling wired-OR configuration without external logic when combined with microprocessor NMI inputs.

Key Specifications

Pinout & Package

UCC3946N is packaged in an 8-pin plastic DIP (N package), with 0.3-inch body width and through-hole mounting. Pin functions are electrically identical to SOIC-8 (D) and TSSOP-8 (PW) variants per datasheet UDG-98001.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX692AESA+ and TPS3808G33DBVR, the UCC3946N uniquely offers full programmability of reset threshold, reset period, and watchdog period using only passive components-enabling one IC to cover multiple voltage rails and timing requirements without redesign.

Availability

UCC3946N is available at Aetrix Electronics and suitable for industrial PLC controllers, medical infusion pumps, smart energy meters, and automotive body control modules requiring stable component supply and long-term manufacturability.

Supply support for UCC3946N 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 delivering analog, embedded processing, and connectivity solutions for industrial, automotive, and communications markets.

The UCC3946N belongs to TI's microprocessor supervisor product line, designed specifically for robust, low-power, and field-programmable reset and watchdog supervision in mission-critical embedded systems.

FAQ

What is the minimum VDD voltage at which UCC3946N guarantees valid reset assertion?

The UCC3946N guarantees RES is asserted and valid down to VDD = 1.0 V, as specified in the Electrical Characteristics table (Note 1). This ensures reliable reset behavior during deep brownout or capacitor discharge events, unlike many supervisors that require ≥1.8 V to function. The UCC3946N achieves this via optimized internal biasing and low-voltage comparator design, making it suitable for battery-backed or energy-harvesting applications where supply collapse must be detected early.

How does the UCC3946N implement programmable reset threshold?

The UCC3946N uses an internal 1.235 V precision reference applied to the RTH pin, where an external resistor divider (R1/R2) scales the monitored voltage (e.g., VDD) to match that reference. The reset threshold is calculated as V_RESET = 1.235 × (R1 + R2)/R2. This method allows setting thresholds from ~1.8 V to 5.5 V using standard 1% resistors, and the UCC3946N's high-impedance RTH input (5 nA leakage) ensures minimal loading on the divider network.

Can the UCC3946N watchdog and reset outputs be directly connected together?

Yes, RES and WDO can be wired together because both are open-drain outputs. When either signal pulls low, the combined node goes low - effectively performing a logical OR. However, if one output drives high while the other pulls low, additional current flows from VDD through the high-side driver into the low-side sink. For fault-tolerant designs, TI recommends using an external OR gate instead, especially in systems where current budget during faults is constrained. The UCC3946N datasheet explicitly validates this wired-OR usage in "Connecting WDO to RES" (p. 5).

What capacitor types are recommended for RP and WP pins on the UCC3946N?

TI specifies NPO (C0G) ceramic capacitors for both RP and WP timing connections due to their low leakage, tight tolerance, and minimal voltage coefficient. These characteristics preserve timing accuracy across temperature and voltage, critical for the 400 nA current-source-based timing (TRP = 3.125 × CRP, TWP = 25 × CWP). X7R or Y5V ceramics are discouraged due to higher leakage and capacitance drift, which can cause significant watchdog or reset period deviation - particularly at elevated temperatures or after long-term bias stress.

Does the UCC3946N support manual reset functionality?

Yes, the UCC3946N supports manual reset by placing a momentary push-button switch in parallel with R2 in the RTH resistor divider network. Pressing the switch shorts R2, forcing the RTH voltage below 1.235 V and triggering RES assertion for the full programmed reset period. This implementation requires no additional IC pins or external logic, and the UCC3946N's ability to assert RES down to 1 V ensures manual reset works even during low-supply conditions - a feature confirmed in the Functional Description and Application Information sections of SLUS247B.