Overview
The UCC3946DTR, produced by Texas Instruments, is a microprocessor supervisor with a watchdog timer designed to provide accurate supervision and protection for microprocessor systems. This device ensures that the microprocessor operates within safe voltage levels and monitors its activity to prevent malfunctions. It is available in an 8-pin SOIC (D) package, making it suitable for a variety of applications where space is a concern.
Key Specifications
| Parameter | Min | Typ | Max | Unit |
|---|---|---|---|---|
| Operating Voltage (VDD) | 2.0 | 5.5 | V | |
| Minimum Operating Voltage (VDD) | 1.0 | V | ||
| Supply Current (IDD) | 10 | 18 | µA | |
| Reset Threshold Voltage | 1.190 | 1.235 | 1.260 | V |
| Reset Period (CRP = 64 nF) | 160 | 200 | 260 | ms |
| Watchdog Period (CRP = 64 nF) | 1.12 | 1.60 | 2.08 | s |
| Input Leakage Current | 5 | nA | ||
| High-Level Output Voltage (ISOURCE = 2 mA) | VDD - 0.3 | V | ||
| Low-Level Output Voltage (ISINK = 2 mA) | 0.1 | V |
Key Features
- Fully programmable reset threshold and reset period using external resistors and capacitors.
- Fully programmable watchdog period using an external capacitor.
- 2% accurate reset threshold.
- Input voltage down to 2 V with a maximum input current of 18 µA.
- Reset valid down to 1 V.
- Glitch immunity on the VDD line to prevent erratic operation due to noise.
- Separate outputs for reset (RES) and watchdog (WDO) signals.
- Available in 8-pin SOIC (D) and TSSOP (PW) packages.
Applications
The UCC3946DTR is suitable for a variety of microprocessor applications where reliable supervision and watchdog functions are critical. It prevents the microprocessor from executing code during undervoltage conditions, typically during power-up and power-down. The watchdog circuit monitors the microprocessor’s activity, ensuring that if the microprocessor fails to toggle the watchdog input within the programmed period, an error recovery routine can be initiated.
Q & A
- What is the primary function of the UCC3946DTR?
The primary function is to provide accurate microprocessor supervision, including reset and watchdog functions. - What is the operating voltage range for the UCC3946DTR?
The operating voltage range is from 2.0 V to 5.5 V. - How is the reset threshold voltage programmed?
The reset threshold voltage can be programmed using two external resistors. - What is the minimum operating voltage for valid reset?
The minimum operating voltage for a valid reset is 1.0 V. - How does the watchdog function work?
The watchdog function monitors the microprocessor’s activity. If the watchdog input is not toggled within the programmed period, the watchdog output (WDO) is asserted low. - What are the available package types for the UCC3946DTR?
The device is available in 8-pin SOIC (D) and TSSOP (PW) packages. - How can the reset and watchdog outputs be connected for design flexibility?
The reset and watchdog outputs can be connected to provide design flexibility. For example, WDO can be connected to RES, or they can be connected to the inputs of an OR gate whose output is connected to the microprocessor’s reset pin. - What precautions should be taken during layout and design?
Precautions include using a 0.1-µF capacitor to decouple the VDD supply, keeping trace lengths minimal for precision current sources, and routing high voltage and high-speed signals away from sensitive components. - What is the significance of the reset period and watchdog period?
The reset period ensures the microprocessor is held in reset until the voltage stabilizes above the threshold. The watchdog period ensures the microprocessor is active and toggling the watchdog input within a specified time to prevent system malfunctions. - How does the device handle voltage glitches?
The device ignores voltage glitches that are below a certain magnitude and duration, preventing erratic operation due to noise.
