The MAX791 microprocessor (µP) supervisory circuit reduces the complexity and number of components needed to monitor power-supply and battery-control functions in µP systems. It is characterized by low power consumption and fast response time, making it suitable for both portable equipment and high-performance equipment. The MAX791 provides various functions, including µP reset, manual reset input, power-fail and low-battery detection, backup-battery switchover, software monitoring of backup-battery voltage, watchdog-fault output, and write protection of CMOS RAM or EEPROM.
The MAX791 microprocessor supervisory circuit reduces component count for monitoring power‑supply and battery‑control functions in µP systems. It operates with a 50 µA supply current, 250 mA output capability (25 mA in battery‑backup mode), and supports multiple package types (DIP, TSSOP, SO). The device provides µP reset, manual‑reset input, 1.25 V threshold detection, two‑stage power‑fail warning, backup‑battery switchover, watchdog timer, and write‑protect features.
The datasheet details electrical characteristics, pin descriptions, timing diagrams, and watchdog operation. It specifies input voltage ranges (‑0.3 V to +6 V), operating temperature ranges (0 °C to +70 °C for MAX791C, –40 °C to +85 °C for MAX791E, –55 °C to +125 °C for MAX791MJE), and the formula for setting the watchdog timeout period.
| Supply current (normal mode) | 50 µA |
|---|---|
| Output current (normal mode) | 250 mA (25 mA in battery‑backup mode) |
| Input voltage range (VCC) | -0.3 V to +6 V |
| Input voltage range (VBATT) | -0.3 V to +6 V |
| Operating temperature (MAX791E) | -40 °C to +85 °C |
| Watchdog default timeout | 1.6 s |
| Watchdog timeout formula | 2.1 × (capacitor nF) ms |
The MAX791 draws about 50 µA of supply current in normal mode.
It can source up to 250 mA, or 25 mA when operating in battery‑backup mode.
Connect a capacitor between the SWT pin and ground; the timeout equals 2.1 × (capacitor nF) ms.