MAX792MCSLASHD datasheet(11/16 Pages) MAXIM

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Microprocessor and Non-Volatile

Memory Supervisory Circuits

______________________________________________________________________________________

Reset Outputs (RESET and RESET)

The RESET output is active low and typically sinks 1.6mA

at 0.1V. When deasserted, RESET sources 1.6mA at typi-

cally VCC - 1.5V. The RESET output is the inverse of

RESET. RESET is guaranteed to be valid down to VCC = 1V,

and an external 10k

Ω pull-down resistor on RESET

ensures that it will be valid with VCC down to GND

(Figure 5). As VCC goes below 1V, the gate drive to the

RESET output switch reduces accordingly, increasing the

rDS(ON) and the saturation voltage. The 10kΩ pull-down

resistor ensures that the parallel combination of switch

plus resistor will be around 10k

Ω and the saturation

voltage will be below 0.4V while sinking 40µA. When

using an external pull-down resistor of 10k

Ω, the high

state for the RESET output with VCC = 4.75V is typically

4.60V.

Overvoltage Comparator

The overvoltage comparator is an uncommitted com-

parator that has no effect on the operation of other chip

functions. Use this input to provide overvoltage indica-

tion by connecting a voltage divider from the input sup-

ply, as in Figure 6.

Connect OVI to ground if the overvoltage function is not

used. OVO goes low when OVI goes above 1.30V. With

OVI below 1.30V, OVO is actively pulled to VCC and can

source1µA.

Watchdog Function

The watchdog monitors µP activity via the watchdog

input (WDI). If the µP becomes inactive, WDO and WDPO

are asserted. To use the watchdog function, connect

WDI to a µP bus line or I/O line. If WDI remains high or

low for longer than the watchdog timeout period

(1.6sec nominal), WDPO and WDO are asserted, indicat-

ing a software fault condition (see

Watchdog-Pulse

Output and Watchdog Output sections).

Watchdog Input

If the watchdog function is unused, connect WDI to VCC

or GND. A change of state (high-to-low, low-to-high, or

a minimum 100ns pulse) at WDI during the watchdog

period resets the watchdog timer. The watchdog timer

MAX792

MAX820

GND

VCC

REGULATOR

µP

µP NMI

RESET IN/INT

LLIN/REFOUT

RESET

LOW LINE

VLOW LINE = 1.3

R1 + R2

)

(

VRESET = 1.3 R3 + R4

R4 )

(

Figure 4c. Alternative Connection for External Programming Mode

RESET

MAX792

MAX820

µP RESET

10k

Figure 5. Adding an external pull-down resistor ensures RESET

is valid with VCC down to GND.

MAX792

MAX820

GND

VCC

OVI

OVO

OVERVOLTAGE

VOLTAGE REGULATOR

1.30V

Figure 6. Detecting an Overvoltage Condition

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