onsemi CAT824RSDI-GT3

Overview

CAT824RSDI-GT3 from onsemi is a system supervisory voltage reset IC with watchdog timer and active-high reset output, designed for brownout detection and power-on reset in 2.5 V microcontroller systems. It features a 2.63 V reset threshold, 140–400 ms reset timeout, 1.12–3.20 s watchdog timeout, TSOT-23-5 package, and operates from −40°C to +85°C.

For engineers reviewing the CAT824RSDI-GT3 datasheet, pinout, applications, or equivalent options, key selection criteria include reset threshold accuracy (±2.5% over temperature), WDI input compatibility with CMOS-level processor outputs, push-pull RESET output drive capability (3.2 mA sink at V_RST min), and manual reset absence-distinguishing it from CAT823 variants.

Technical Context

The CAT824RSDI-GT3 implements a precision bandgap-based voltage reference with 40 ppm/°C tempco and internal hysteresis (5 mV) to ensure stable brownout detection across temperature. Its digital delay block enforces a minimum 140 ms reset assertion after V_CC exceeds the trip point, independent of supply ramp rate.

Watchdog functionality relies on edge-triggered timing: any low-to-high or high-to-low transition on WDI resets a 1.12–3.20 s timeout counter; failure to strobe within that window forces RESET active for t_RP. The WDI input accepts standard CMOS logic levels (V_IL = 0.3×V_CC, V_IH = 0.7×V_CC) and draws ≤160 µA average current.

Key Specifications

Pinout & Package

Package: TSOT-23-5 (Case 419AE), 2.90 mm × 1.60 mm × 0.95 mm body, 0.95 mm pitch, Pb-free NiPdAu finish, RoHS compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CAT824RSDI-GT3, MAX824RUS+T offers identical function and pinout but trades higher supply current for broader vendor support, while TPS3808G12DBVR provides threshold flexibility at the cost of watchdog capability - making CAT824RSDI-GT3 optimal for fixed-threshold, watchdog-reliant industrial control.

Availability

CAT824RSDI-GT3 is available at Aetrix Electronics and suitable for industrial automation, medical device monitoring, smart metering, and automotive body electronics requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CAT824RSDI-GT3 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The CAT82x series is part of onsemi's system supervision portfolio, engineered specifically for robust, low-power reset and watchdog functions in resource-constrained embedded systems where reliability under voltage transients is critical.

FAQ

What is the exact reset threshold voltage of the CAT824RSDI-GT3 and how tightly is it specified?

The CAT824RSDI-GT3 has a nominal reset threshold of 2.63 V, with a guaranteed range of 2.55 V to 2.70 V over the full −40°C to +85°C operating temperature range. This ±2.5% tolerance ensures consistent brownout detection for 2.5 V systems without requiring calibration or external trimming. The threshold is derived from an internal bandgap reference with 40 ppm/°C tempco, minimizing drift across thermal conditions.

Does the CAT824RSDI-GT3 include a manual reset input like the CAT823 family?

No, the CAT824RSDI-GT3 does not include a manual reset (MR) input. Unlike the CAT823, which features an MR pin for pushbutton or processor-initiated reset, the CAT824RSDI-GT3 is configured exclusively for power-supply monitoring and watchdog supervision. Its pinout consists of V_CC, WDI, RESET (active-high), GND, and RESET (active-low) - omitting MR entirely. This simplifies layout for designs where external reset initiation is unnecessary.

How does the watchdog timeout behavior work on the CAT824RSDI-GT3, and what happens if the WDI pin is left floating?

The CAT824RSDI-GT3 watchdog timer times out after 1.12–3.20 s if no valid edge (low-to-high or high-to-low) occurs on the WDI pin. If WDI is left floating or tri-stated, the device detects the open condition and internally toggles WDI low for 7/8ths of the timeout period and high for 1/8th - repeating continuously. This prevents unintended resets while signaling the watchdog is disabled, allowing safe operation without processor intervention.

Can the CAT824RSDI-GT3 operate reliably at V_CC levels below 2.5 V, and what is its minimum functional supply voltage?

Yes, the CAT824RSDI-GT3 is fully specified to operate down to V_CC = 1.2 V across −40°C to +85°C, per Table 2 of the datasheet. Its RESET output remains valid (VOH ≥ 0.8×V_CC, VOL ≤ 0.3 V) even at 1.2 V, and the internal voltage reference continues functioning. This enables robust reset assertion during deep brownout events - critical for preserving state in battery-backed systems before complete power loss.

What is the purpose of the dual RESET outputs (active-high and active-low) on the CAT824RSDI-GT3?

The CAT824RSDI-GT3 provides both RESET (active-high) and RESET (active-low) outputs to interface natively with diverse microcontroller and peripheral IC reset architectures. Many legacy MCUs require active-low reset, while newer low-power SoCs often accept active-high. Having both outputs on a single device eliminates external inverters or dual-supervisor solutions, reducing component count, PCB area, and signal path complexity in mixed-vendor designs.