Descripción general

The MAX803/MAX809/MAX810 are microprocessor (μP) supervisory circuits used to monitor the power supplies in μP and digital systems. They provide excellent circuit reliability and low cost by eliminating external components and adjustments when used with +5V, +3.3V, +3.0V, or +2.5V powered circuits.

These circuits perform a single function: they assert a reset signal whenever the VCC supply voltage declines below a preset threshold, keeping it asserted for at least 140ms after VCC has risen above the reset threshold. Reset thresholds suitable for operation with a variety of supply voltages are available.

The MAX803 has an open-drain output stage, while the MAX809/MAX810 have push-pull outputs. The MAX803’s open-drain RESET output requires a pullup resistor that can be connected to a voltage higher than VCC. The MAX803/MAX809 have an active-low RESET output, while the MAX810 has an active-high RESET output. The reset comparator is designed to ignore fast transients on VCC, and the outputs are guaranteed to be in the correct logic state for VCC down to 1V.

Low supply current makes the MAX803/MAX809/MAX810 ideal for use in portable equipment. The MAX803 is available in a 3-pin SC70 package, and the MAX809/MAX810 are available in 3-pin SC70 or SOT23 packages.

 

Aplicaciones

Ordenadores

Controladores

Intelligent Instruments

Critical μP and μC Power Monitoring

Portable/Battery-Powered Equipment

Automoción

 

Ventajas y características

Precision Monitoring of +2.5V, +3V, +3.3V, and  +5V Power-Supply Voltages

Fully Specified Over Temperature

Available in Three Output Configurations

Open-Drain RESET Output (MAX803)

Push-Pull RESET Output (MAX809)

Push-Pull RESET Output (MAX810)

140ms (min) Power-On-Reset Pulse Width

12μA Supply Current

Guaranteed Reset Valid to VCC = +1V

Power Supply Transient Immunity

No External Components

3-Pin SC70 and SOT23 Packages

AEC-Q100 Qualified.

 

Descripción detallada

A microprocessor’s (μP’s) reset input starts the μP in a known state. The MAX803/MAX809/MAX810 assert reset to prevent code-execution errors during power-up, powerdown, or brownout conditions. They assert a reset signal whenever the VCC supply voltage declines below a preset threshold, keeping it asserted for at least 140ms after VCC has risen above the reset threshold. The MAX803 uses an open-drain output, and the MAX809/MAX810 have a push-pull output stage. Connect a pullup resistor on the MAX803’s RESET output to any supply between 0 and 6V.

 

Información sobre aplicaciones

Negative-Going VCC Transients

In addition to issuing a reset to the μP during power-up, power-down, and brownout conditions, the MAX803/MAX809/MAX810 are relatively immune to short-duration negative-going VCC transients (glitches).

Reset comparator overdrive, for which the MAX803/MAX809/MAX810 do not generate a reset pulse. The graph was generated using a negative-going pulse applied to VCC, starting 0.5V above the actual reset threshold and ending below it by the magnitude indicated (reset comparator overdrive). The graph indicates the maximum pulse width a negative-going VCC transient can have without causing a reset pulse. As the magnitude of the transient increases (goes farther below the reset threshold), the maximum allowable pulse width decreases. Typically, for the MAX8__L and MAX8__M, a VCC transient that goes 100mV below the reset threshold and lasts 20μs or less will not cause a reset pulse. A 0.1μF bypass capacitor mounted as close as possible to the VCC pin provides additional transient immunity.

 

Ensuring a Valid Reset Output Down to  VCC = 0V

When VCC falls below 1V, the MAX809 RESET output no longer sinks current—it becomes an open circuit.

Therefore, high-impedance CMOS logic inputs connected to RESET can drift to undetermined voltages. This presents no problem in most applications since most μP and other circuitry is inoperative with VCC below 1V. However, in applications where RESET must be valid down to 0V, adding a pull-down resistor to RESET causes any stray leakage currents to flow to ground, holding RESET low. R1’s value is not critical; 100kΩ is large enough not to load RESET and small enough to pull RESET to ground.