Description générale

The MAX6301–MAX6304 low-power microprocessor (µP) supervisory circuits provide maximum adjustability for reset and watchdog functions. The reset threshold can be adjusted to any voltage above 1.22V, using external resistors. In addition, the reset and watchdog timeout periods are adjustable using external capacitors. A watchdog select pin extends the watchdog timeout period to 500x. The reset function features immunity to power-supply transients.

These four devices differ only in the structure of their reset outputs (see the Selector Guide). The MAX6301–MAX6304 are available in the space-saving 8-pin µMAX package, as well as 8-pin PDIP and SO packages.

 

Applications

Équipement médical

Embedded Controllers

Instruments intelligents

Critical µP Monitoring

Portable Equipment

Set-Top Boxes

Battery-Powered

Ordinateurs

Computers/Controllers

 

Caractéristiques

Adjustable Reset Threshold

Adjustable Reset Timeout

Adjustable Watchdog Timeout

500x Watchdog Timeout Multiplier

4µA Supply Current

RESET or RESETOutput Options

Push-Pull or Open-Drain Output Options

Guaranteed RESETAsserted At or Above

VCC= 1V (MAX6301/MAX6303)

Immunité aux transitoires de l'alimentation

Watchdog Function can be Disabled

PDIP/SO/µMAX Packages Available

 

Description détaillée

Reset Function/Output

The reset output is typically connected to the reset input of a µP. A µP’s reset input starts or restarts the µP in a known state. The MAX6301–MAX6304 µP supervisory circuits provide the reset logic to prevent code-execution errors during power-up, power-down, and brownout conditions.

For the MAX6301/MAX6303, RESET changes from high to low whenever the monitored voltage (VIN) drops below the reset threshold voltage (VRST). RESET remains low as long as VIN is below VRST. Once VIN exceeds VRST, RESET remains low for the reset timeout period, then goes high. When a reset is asserted due to a watchdog timeout condition, RESET stays low for the reset timeout period. Any time reset asserts, the watchdog timer clears. At the end of the reset timeout period, RESET goes high and the watchdog timer is restarted from zero. If the watchdog timeout period is exceeded again, then RESET goes low again. This cycle continues unless WDI receives a transition.

On power-up, once VCC reaches 1V, RESET is guaranteed to be a logic-low. For information about applications where VCC is less than 1V, see the Ensuring a Valid RESET/RESET Output Down to VCC = 0V (MAX6303/MAX6304) section. As VCC rises, RESET remains low. When VIN rises above VRST, the reset timer starts and RESET remains low. When the reset timeout period ends, RESET goes high.

On power-down, once VIN goes below VRST, RESET goes low and is guaranteed to be low until VCC drops below 1V. The MAX6302/MAX6304 active-high RESET output is the inverse of the MAX6301/MAX6303 active-low RESET output, and is guaranteed valid for VCC > 1.31V

Reset Threshold

These supervisors monitor the voltage on RESET IN. The MAX6301–MAX6304 have an adjustable reset threshold voltage (VRST) set with an external resistor voltage-divider.

Watchdog Timer

The MAX6301–MAX6304 feature two modes of watchdog timer operation: normal mode and extended mode. In normal mode (WDS = GND), the watchdog timeout period is determined by the value of the capacitor connected between SWT and ground (see the Selecting the Reset and Watchdog Timeout Capacitor section). In extended mode (WDS = VCC), the watchdog timeout period is multiplied by 500. For example, in the extended mode, a 1µF capacitor gives a watchdog timeout period of 22 minutes.

In extended mode, the watchdog function can be disabled by leaving WDI unconnected or by three-stating the driver connected to WDI. In this mode, the watchdog input is internally driven low during the watchdog timeout period, then momentarily pulses high, resetting the watchdog counter. When WDI is left unconnected, the watchdog timer is cleared by this internal driver just before the timeout period is reached (the internal driver pulls WDI high at about 94% of tWD). When WDI is three-stated, the maximum allowable leakage current of the device driving WDI is 10µA.

Wake-Up Timer

In some applications, it is advantageous to put a µP into sleep mode, periodically wake it up to perform checks and/or tasks, then put it back into sleep mode. The MAX6301 family of supervisors can easily accommodate this technique.