±1% Accuracy, Low-Power, +3V and +5V

µP Supervisory Circuits

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7

_______________Detailed Description

The MAX814/MAX815/MAX816 are high-accuracy, low-

power microprocessor (µP) supervisory circuits. They

have µP-reset, watchdog-timer, and power-fail func-

tions. Typical applications illustrating their similarities

and differences are shown in Figures 1, 2, and 3.

Figures 4, 5, and 6 show the block diagrams of these

parts.

______________________________________________________________Pin Description

PIN

MAX814

MAX815

MAX816

NAME

FUNCTION

1

1

1

MR

Manual-Reset Input. Triggers a reset when pulled below 1.10V. This active-

with CMOS logic or shorted to GND with a switch or transistor.

2

2

—

voltage*, RESET is low, and remains low for a minimum of 140ms after

it rises above the threshold.

—

—

2

Positive Power-Supply Input. On the MAX816, RESET is controlled by

3

3

3

GND

Ground

4

4

4

PFI

Power-Fail Input. The PFI threshold voltage is 1.70V on the MAX816 and on

MAX814/MAX815 parts with the T suffix. It is 2.50V on MAX814/MAX815

5

5

5

PFO

Power-Fail Output. When PFI is below its threshold, PFO is low;

otherwise it is high.

—

6

—

WDI

Watchdog CMOS Input. If WDI remains high or low for more than 1.56s, the

watchdog timer times out, and WDO goes low. The timer is reset to

zero on each WDI transition.

6

—

—

LOW LINE

low-line threshold.

—

—

6

RESET IN

Reset Comparator Input. Reference is 1.70V. When RESET IN is below

1.70V, RESET is low, and remains low for a minimum of 140ms after it rises

above the reference.

7

7

7

RESET

Reset Output. Normally high, active low. Controlled by MR and reset

comparator.

8

—

8

RESET

Reset Output. Active high. The inverse of RESET.

—

8

—

WDO

threshold comparator input voltage is low or when the watchdog timer

times out. There is no appreciable delay going either direction when the

*Reset Threshold Voltage is determined by part number suffix: K = 4.80V, L = 4.70V, N = 4.55V, T = 3.03V.