onsemi NCP803SN308T1G 3.08V Voltage Supervisor: Features and Application Design Guide
Voltage supervisors, also known as voltage monitors or reset ICs, are critical components in modern electronic systems, ensuring controlled and predictable operation by monitoring power supply rails. The onsemi NCP803SN308T1G is a high-performance microprocessor supervisor circuit designed to provide a reset signal to the host system when the supply voltage drops below a predefined threshold. This device is engineered for precision and reliability in a compact package, making it an ideal choice for a wide array of applications, including embedded systems, automotive electronics, industrial controls, and portable consumer devices.
Key Features
The NCP803SN308T1G integrates several advanced features that enhance system integrity and simplify design:
Precision Voltage Monitoring: The core function of this IC is to monitor the VCC supply voltage. It is factory-trimmed for a fixed threshold voltage of 3.08V, offering high accuracy to ensure the microprocessor operates only within its specified voltage range.
Assertion on Power-Up and Power-Down: The device asserts a reset signal whenever VCC is below the threshold voltage. This ensures the system starts in a known state during power-up and is held in reset during power-down or brownout conditions, preventing erratic operation.
Manual Reset Input: A key feature is the inclusion of a Manual Reset (MR) input. This allows an external switch, processor, or other logic circuit to force a system reset on demand, providing designers with greater control over system initialization and debugging.
Guaranteed Reset Output Valid to VCC = 1.0V: The open-drain RESET output remains valid and actively holds the reset signal low even as VCC decays to as low as 1.0V. This is crucial for maintaining system stability during severe brownout events.
Low Power Consumption: The device features very low supply current, typically drawing only 9.5 µA. This makes it exceptionally suitable for battery-powered and portable applications where power efficiency is paramount.
Small Form Factor: Housed in a space-saving SOT-23-5 package, it is designed for high-density PCB layouts.
Application Design Guide
Integrating the NCP803SN308T1G into a system is straightforward, but following best practices is essential for optimal performance.
1. Basic Connection:
The typical application circuit is simple. VCC and GND are connected to the power supply rail being monitored. The open-drain RESET output requires a pull-up resistor (typically 10 kΩ to 100 kΩ) to the logic voltage rail of the microprocessor (which can be different from the monitored VCC). The Manual Reset (MR) pin can be left floating or connected to a push-button switch for user-initiated reset; it is active-low and requires a pull-up resistor to VCC if connected to a switch.
2. PCB Layout Considerations:
For noise immunity, it is recommended to place a decoupling capacitor (100 nF) as close as possible to the VCC pin and the device's ground connection. Keep the traces to the MR input and the RESET output short to minimize noise pickup and ensure signal integrity.
3. Selecting the Pull-Up Resistor (for RESET):
The value of the pull-up resistor on the RESET output is a trade-off between power consumption and switching speed. A lower value provides faster rise times but increases current consumption when the output is asserted low. A value between 10 kΩ and 100 kΩ is generally suitable for most applications.
4. Using the Manual Reset Function:
The MR pin provides design flexibility. It can be connected to a simple tactile switch for user interaction. Furthermore, it can be driven by another logic signal from a secondary processor or a system watchdog timer to create a more robust supervisory scheme, allowing one subsystem to reset another.
5. Handling Multiple Voltage Rails:
Since the RESET output is open-drain, it can be pulled up to a voltage rail different from the monitored VCC. This allows a single 3.08V supervisor to correctly interface with a microprocessor running on a lower core voltage (e.g., 1.8V or 2.5V) by simply pulling the RESET output to the microprocessor's logic voltage level.
In summary, the onsemi NCP803SN308T1G is a highly reliable and precise voltage supervisor. Its combination of a fixed threshold, manual reset capability, ultra-low power consumption, and stable operation down to low voltages makes it an excellent choice for ensuring system stability in a diverse range of electronic products. Its simple integration and robust feature set provide designers with a critical tool for enhancing product reliability.
Keywords: Voltage Supervisor, Manual Reset, Power Management, Brownout Protection, Low Power Consumption
