Voltage Detector# Technical Documentation: KA75390Z Voltage Detector
Manufacturer : FSC (Fairchild Semiconductor)
Component Type : Voltage Detector / Reset IC
Document Version : 1.0
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## 1. Application Scenarios
### 1.1 Typical Use Cases
The KA75390Z is a dual-voltage detector IC primarily designed for system reset and power monitoring applications in embedded systems. Its core function is to monitor two independent voltage rails and generate a reset signal when either falls below a predefined threshold.
Primary applications include:
- Microcontroller/Microprocessor Reset Circuits : Provides reliable power-on reset (POR) and brown-out reset (BOR) functionality for digital processors during initial power-up, shutdown, or voltage dips.
- Battery-Powered Device Monitoring : Monitors main battery voltage and backup battery/supercapacitor voltage in portable electronics (e.g., handheld meters, data loggers) to initiate data save routines before power loss.
- Sequential Power-Up/Down Control : In multi-rail systems (e.g., +5V and +3.3V), ensures that a processor remains in reset until all monitored supplies are stable, preventing erratic boot behavior.
- Fail-Safe System Monitoring : Used in automotive, industrial control, or safety systems to detect power supply faults and force a controlled system shutdown or alarm state.
### 1.2 Industry Applications
- Consumer Electronics : Set-top boxes, routers, smart home controllers, and gaming consoles for stable boot sequencing.
- Industrial Automation : PLCs (Programmable Logic Controllers), sensor interfaces, and motor drives where supply integrity is critical.
- Telecommunications : Network switches, baseband units, and line cards requiring reliable reset management.
- Automotive Electronics : Body control modules and infotainment systems (within specified temperature grades).
- Medical Devices : Portable diagnostic equipment where controlled shutdown during low battery is essential for data integrity.
### 1.3 Practical Advantages and Limitations
Advantages:
- Integrated Dual Comparator : Monitors two voltages with one IC, reducing part count and board space.
- Low Quiescent Current : Typically 35µA, suitable for battery-sensitive applications.
- Precision Thresholds : Factory-trimmed detection thresholds (e.g., 4.55V and 2.93V for common variants) with tight tolerance (±2.5%).
- Built-in Hysteresis : Prevents output oscillation ("chatter") near the detection threshold during noisy or slowly varying supply conditions.
- Open-Drain Outputs : Allow flexible interfacing and wired-OR configurations for multi-source reset signals.
Limitations:
- Fixed Threshold Voltages : The detection voltage (`V_{DET}`) is factory-set and not user-adjustable. Designers must select a variant (e.g., KA75390Z-5 for 5V detection) matching their system voltage.
- Limited Output Drive : The open-drain outputs require an external pull-up resistor; they cannot source current directly.
- Temperature Dependency : Threshold voltage has a defined temperature coefficient (typically ~±100ppm/°C), which must be accounted for in wide-temperature designs.
- No Built-in Time Delay : Requires an external capacitor on the `CD` pin to create a power-on reset delay; improper selection can cause timing issues.
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## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
| Pitfall | Consequence | Solution |
| :--- | :--- | :--- |
| Incorrect Variant Selection | Detector may trip too early or too late, causing unstable resets. | Verify suffix code (e.g., `-5`) matches the desired detection voltage. Cross-reference datasheet tables. |
| Missing/Improper Pull-Up Resistor | Open-drain
