3-PIN MICROPROCESSOR RESET CIRCUITS # Technical Documentation: APX80940SAG7 Voltage Supervisor
Manufacturer : DIODES Incorporated
Component Type : Voltage Supervisor / Reset IC
Document Version : 1.0
Date : October 2023
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## 1. Application Scenarios
### 1.1 Typical Use Cases
The APX80940SAG7 is a precision voltage supervisor designed primarily for monitoring power supply rails in embedded systems. Its core function is to assert a reset signal when the monitored voltage falls below a predefined threshold, ensuring controlled system initialization and shutdown.
Primary Applications Include:
- Microcontroller/Microprocessor Reset Circuits : Provides reliable power-on reset (POR) and brown-out reset (BOR) functionality for devices such as ARM Cortex-M cores, PIC, AVR, and 8051 variants.
- Battery-Powered Equipment : Monitors battery voltage in portable devices (e.g., IoT sensors, wearables, handheld medical devices) to prevent erratic operation during low-battery conditions.
- Industrial Control Systems : Ensures safe operation of PLCs, motor controllers, and sensor interfaces by resetting logic during undervoltage events.
- Automotive Electronics : Used in infotainment systems, body control modules (BCMs), and telematics where stable voltage supervision is critical (note: may require additional qualification for automotive-grade use).
- Consumer Electronics : TVs, set-top boxes, and smart home devices where controlled startup and shutdown prevent data corruption.
### 1.2 Industry Applications
- IoT & Edge Computing : Deployed in gateway devices and edge nodes to maintain reliability during power fluctuations.
- Telecommunications : Provides reset management in routers, switches, and baseband units.
- Medical Devices : Ensures patient safety in diagnostic equipment (e.g., glucose monitors, portable ECG) by preventing malfunction during voltage dips.
- Renewable Energy Systems : Supervises DC rails in solar inverters and charge controllers.
### 1.3 Practical Advantages and Limitations
Advantages:
- Low Quiescent Current : Typically 3.5 µA, making it suitable for battery-operated applications.
- Precision Threshold : Factory-trimmed threshold voltage (e.g., 4.40V for APX80940SAG7) with ±1.5% accuracy ensures reliable monitoring.
- Small Footprint : Available in SOT-23-3 package, saving PCB space.
- Manual Reset Capability : Some variants include a manual reset input (MR pin) for external control (note: APX80940SAG7 is a 3-pin device without MR).
- Wide Operating Range : Operates from 1.0V to 5.5V, compatible with 3.3V and 5V systems.
Limitations:
- Fixed Threshold : The threshold voltage is factory-set (non-adjustable), limiting flexibility compared to programmable supervisors.
- No Watchdog Timer : Lacks integrated watchdog functionality, which may require an additional IC for systems needing periodic reset supervision.
- Limited Output Drive : RESET output is typically rated for 10 mA; may require a buffer for driving multiple loads.
- Temperature Sensitivity : Threshold accuracy may drift at temperature extremes (specified over -40°C to +85°C).
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## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
| Pitfall | Solution |
|---------|----------|
| Inadequate Decoupling | Place a 0.1 µF ceramic capacitor within 5 mm of the VCC pin to suppress noise. |
| RESET Output Overload | Avoid connecting directly to high-capacitance loads; use a series resistor (e.g., 100 Ω) if needed. |
| Slow VCC Rise Time | Ensure VCC rise time is
