Design Guide for Power Supply Circuits Using the onsemi MC34064D Undervoltage Sensing IC

Introduction

The onsemi MC34064D is a monolithic undervoltage sensing IC specifically designed for use as a reset controller in power supply applications. It monitors the voltage level of a power rail and provides a reset signal to microprocessors or other digital systems when the supply voltage drops below a predefined threshold. This ensures system stability and prevents erratic operation during power-up, power-down, or brownout conditions. This design guide covers key considerations for integrating the MC34064D into power supply circuits.

Key Features and Operating Principles

The MC34064D operates with a fixed detection threshold of typically 4.65V, making it suitable for 5V power supply systems. It features an open-collector output, which allows flexibility in interfacing with various logic levels. The device requires minimal external components, typically only a pull-up resistor and optionally a delay capacitor for reset timing adjustment. When the monitored voltage falls below the threshold, the output actively pulls low, asserting a reset signal. Once the voltage rises above the threshold with sufficient hysteresis, the output releases, allowing the system to operate normally.

Typical Application Circuit

A basic implementation involves connecting the Vcc pin to the monitored power rail (e.g., 5V). The output pin is pulled up to the same rail or another logic-compatible voltage via a resistor (e.g., 10kΩ). A capacitor between the Delay pin and ground can be added to introduce a time delay for the reset release, ensuring the power rail stabilizes before the system resumes operation. This delay is critical for avoiding false resets during transient events.

Design Considerations

1. Threshold Accuracy: The MC34064D has a typical threshold of 4.65V with ±2.5% tolerance. Designers must ensure this aligns with the system’s undervoltage requirements.

2. Hysteresis: The built-in hysteresis (typically 60mV) prevents output oscillation near the threshold voltage.

3. Output Configuration: The open-collector output requires a pull-up resistor; its value should balance power consumption and switching speed.

4. Noise Immunity: Bypass capacitors near the Vcc pin and proper PCB layout are essential to minimize noise interference.

5. Temperature Stability: The threshold voltage remains stable over a wide temperature range (-40°C to +85°C), making it suitable for industrial environments.

Advanced Applications

For non-standard voltage monitoring, an external resistor divider can be used to adjust the effective threshold. However, the MC34064D is optimized for fixed 5V monitoring, and such configurations may require additional validation. It can also be combined with a watchdog timer or other supervisory functions for enhanced system reliability.

Conclusion

The MC34064D provides a simple, cost-effective solution for undervoltage protection in 5V systems. Its robustness and ease of use make it ideal for consumer electronics, industrial controls, and embedded systems. By adhering to the guidelines above, designers can ensure reliable power management and system integrity.

ICGOODFIND: The MC34064D excels in simplicity and reliability for 5V undervoltage monitoring, offering a compact solution with minimal external components. Its fixed threshold and open-collector output make it versatile for reset generation in diverse applications.

Keywords: Undervoltage Protection, Reset Controller, Power Supply Monitoring, Open-Collector Output, Threshold Hysteresis.