To create a basic design with the MAX6877, such as the one in Figure 1, follow these steps:

1.Select the input voltage thresholds for IN1, IN2, and IN3. The input voltages must exceed these thresholds for power-up to begin. Use the following formula to set the resistor-divider values for IN1. (For IN2 or IN3, replace R1 with R3, or R5 and R2 with R4 or R6.)

2.Select the EN/active-low UV threshold using the following formula. EN/active-low UV can also be used as a logic-level input to control power up. If not used, connect EN/active-low UV to ABP.

3.Set the voltage slew rate. (This is the rate at which the voltages at the outputs OUT1, OUT2, OUT3 ramp up and down.) Select capacitor CSLEW by using the following formula:

where CSLEW is in farads, and SR is in V/s. CSLEW must be in the range of 100pF < CSLEW < 1nF.

4.In sequencing-mode only, the voltages come up one after another, separated by a time delay which is set by capacitor CDELAY using the following formula:

where CDELAY is in farads, and tDELAY is in seconds. tDELAY is also the delay time from when all thresholds are exceeded to the start of sequencing or tracking. CDELAY can be safely left out of the circuit, in which case tDELAY becomes the default 200µs.

5.Pick the MOSFETs for each channel. Ensure that the MAX6877 gate-drive circuit can drive the gate capacitance of the MOSFET.

Multiple MAX6877 parts can be connected together by connecting the power-good output of the first device to the enable input (EN/active-low UV) of the next device. For more information, see the data sheet.

Application Note 3918: www.maxim-ic.com/an3918

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MAX6877 specifications

The Maxim MAX6877 is a highly efficient voltage supervisor designed for a wide range of applications, ensuring reliable operation and protection for sensitive electronic devices. This device is particularly well-suited for applications where monitoring power supply voltages is critical, such as in power management systems, consumer electronics, and industrial automation.

One of the key features of the MAX6877 is its low voltage operation, which enables it to monitor supply voltages as low as 0.5V. This makes it ideal for applications utilizing low voltage power supplies, especially in battery-operated devices where efficient energy usage is paramount. The MAX6877 also boasts a precise voltage detection capability with an accuracy of ±2%, ensuring consistent and reliable operation.

A standout characteristic of the MAX6877 is its adjustable reset threshold. Users can tailor the reset voltage to specific requirements using external resistor dividers, providing flexible solutions for various applications. Additionally, the device incorporates a power-on reset function that ensures the system starts only when the supply voltage stabilizes, safeguarding against erratic behavior during power-up conditions.

The MAX6877 employs a watchdog timer feature, which is essential for monitoring the health of a microcontroller or processor. This feature can reset the system if the microcontroller becomes unresponsive, thereby enhancing system reliability and uptime. The watchdog is configurable, allowing designers to set the timeout period according to application needs.

Another impressive aspect of the MAX6877 is its compact design, available in a small SOT-23 package, ensuring minimal footprint on the printed circuit board. This is particularly beneficial in space-constrained designs, such as handheld devices or embedded systems.

The device operates over a wide temperature range, from -40°C to +125°C, making it suitable for both industrial and automotive applications. Additionally, the MAX6877 draws minimal quiescent current, which is advantageous in battery-powered devices, prolonging battery life and improving efficiency.

In summary, the Maxim MAX6877 is a versatile and reliable voltage supervisor, characterized by its low voltage operation, adjustable reset threshold, watchdog timer feature, and compact design. With its robust performance and energy-efficient capabilities, the MAX6877 is an excellent choice for a variety of applications requiring precise voltage management and system reliability.