The **MAX802RC/D** is a Microprocessor ($\mu$P) Supervisory Circuit manufactured by Maxim Integrated (now part of Analog Devices). It is designed to monitor the power supply in microprocessor systems and handle backup-battery switching to ensure data integrity. --- ## 1. Core Functions The MAX802RC/D provides four essential functions to ensure system reliability: 1. **Reset Output:** Asserts a reset signal during power-up, power-down, and brownout conditions. 2. **Battery Backup Switching:** Automatically switches the RAM supply to a backup battery when $V_{CC}$ falls below the battery voltage. 3. **Watchdog Timer:** Monitors software execution; if the processor fails to "pet" the watchdog within 1.6 seconds, it triggers a reset. 4. **Power-Fail Warning:** Includes a 1.25V threshold detector for early warning of power failure before the main supply drops. --- ## 2. Technical Specifications The "R" and "C/D" suffixes denote specific voltage thresholds and temperature ranges. | Parameter | Specification | | :--- | :--- | | **Supply Voltage ($V_{CC}$)** | 1.0V to 5.5V | | **Reset Threshold** | 2.625V (Typical for "R" suffix) | | **Watchdog Timeout** | 1.6 seconds | | **Reset Pulse Width** | 200ms (Typical) | | **Supply Current** | 40µA (Operating), 1µA (Battery Backup mode) | | **Package Type** | Available in 8-pin SOIC or DIP | --- ## 3. Pinout Description | Pin Name | Description | | :--- | :--- | | **$V_{CC}$** | Main Supply Input | | **$V_{OUT}$** | Output to CMOS RAM (switches between $V_{CC}$ and $V_{BATT}$) | | **$V_{BATT}$** | Backup Battery Input | | **GND** | Ground | | **RESET** | Active-low output that triggers when $V_{CC}$ is below threshold | | **WDI** | Watchdog Input (must be toggled to prevent reset) | | **PFI** | Power-Fail Input (compared against 1.25V internal reference) | | **PFO** | Power-Fail Output (goes low when PFI < 1.25V) | --- ## 4. Key Differences: MAX802 vs. MAX702 The **MAX802** is an upgraded version of the industry-standard MAX702. The primary improvements include: * **Lower Supply Current:** More efficient for battery-operated devices. * **Tighter Voltage Thresholds:** Provides more precise monitoring of the power rail. * **Faster Propagation Delay:** Improved response time to power-down events. --- ## 5. Typical Application Circuit ```c // Logical flow of the Watchdog feature while(system_running) { perform_tasks(); toggle_WDI_pin(); // Resets the 1.6s timer if(power_low) { save_to_SRAM(); // MAX802 triggers PFO early } } ```