MAX691EWE

PMIC - Supervisors: MAX691EWE application field and working principle

As a voltage supervisor IC, the MAX691EWE series from Maxim Integrated is suitable for monitoring voltage levels from one supply rail. This series is designed for an operating temperature range of -55°C to +125°C and is available in a variety of packages including SO, TQFN, SOT, and µMAX. With an on-board delay circuit, the supervisor can guarantee a reset signal without interference. It also has a low operating current, making it suitable for use in battery-powered systems.

The MAX691EWE series is used to protect microprocessor circuits or ASICs from power supply failure, or faults in other system components. It can also be used to ensure that the system enters a safe state during system power-up and power-down sequences. Additionally, it can be used to generate a reset signal when the power supply voltage drops below a certain threshold, guaranteeing a stable operating voltage for the microprocessor.

Features

• Very low operating current: 2µA typ.
• Voltage supervisor reset thresholds adjustable from 1.221V to 5.0V in 0.25V increments.
• On-board delay circuit for noise immunity and glitch filtering.
• Reset timeout period: 40ms typ.
• Rotary and switch options to set reset thresholds.
• Wide operating temperature range: -55°C to +125°C.
• Power-on reset signal generated as soon as power is applied.
• Status flag output (RESET74) indicates low-voltage trip.

Applications

• Battery-powered systems.
• Microprocessor circuits or ASICs protection.
• Automotive electronics.
• Consumer and industrial applications.
• Telecommunications.

Working Principles

The MAX691EWE voltage supervisor is designed to monitor the power supply voltage and generate an output reset signal if the voltage falls below the preset reset voltage threshold. It consists of two integrated circuit blocks, an error amplifier and a reset time delay circuit, connected together through an internal voltage divider. An external resistor-divider is also connected to the error amplifier’s non-inverting input for setting the reset voltage threshold.

When the power supply voltage is above the reset voltage threshold, the error amplifier provides a positive feedback voltage to the reset time delay circuit, inhibiting it from issuing a reset signal. At the same time, the output of the error amplifier is low, ensuring that the RESET output of the supervisor is off. When the power supply voltage drops below the reset voltage threshold set by the external voltage divider, the error amplifier switches off, allowing the reset time delay circuit to issue a reset signal.

The MAX691EWE integrates an on-board delay circuit and a filter capacitor, both of which are necessary to guarantee an accurate reset signal without interference. The delay circuit helps to avoid false reset signals due to noise spikes or glitches in the power supply, while the filter capacitor smoothes any rapid changes in the supply voltage.

To ensure proper operation, the MAX691EWE also features an open-drain flag output, RESET74, which indicates a low-voltage trip of the supervisor. This output is used to enable a second level of power monitoring, as it can be connected to an external logic circuit to provide a warning before the supervisor trips.

The MAX691EWE series is a versatile voltage supervisor offering reliable protection and monitoring for a wide variety of applications. Its wide operating temperature range and low operating current make it ideal for battery-powered systems, automotive electronics, telecoms, consumer and industrial equipment.