MAX791CUE 查看數據表（PDF） - Maxim Integrated

零件编号

产品描述 (功能)

生产厂家

MAX791CUE

Microprocessor Supervisory Circuit

Maxim Integrated 

Microprocessor Supervisory Circuit

FROM

REGULATED

SUPPLY

0.1µF

3 VCC

VOUT 2

MAX791

VBATT 1

0.1µF

µP POWER

POWER TO

CMOS RAM

µP

3.0V

RESET 15

LOWLINE 10

WDI 11

RESET

NMI

I/O LINE

GND

a)

4

VOLTAGE

REGULATOR

3 VCC

VOUT 2

0.1

µF

MAX791

VBATT

1

0.1µF

µP POWER

POWER TO

CMOS RAM

µP

3.0V

7 PFI

RESET 15

PFO 6

WDI 11

GND

4

RESET

NMI

I/O LINE

b)

Figure 9. a) If the unregulated supply is inaccessible,

LOWLINE generates the NMI for the µP. b) Use PFO to gener-

ate the µP NMI if the unregulated supply is inaccessible.

Power-Fail Input

PFI is the input to the power-fail comparator. PFI has a

guaranteed input leakage of ±25nA max over tempera-

ture. The typical comparator delay is 15µs from VIL to

VOL (power failing), and 55µs from VIH to VOH (power

being restored). If unused, connect this input to

ground.

Power-Fail Output

The Power-Fail Output (PFO) goes low when PFI goes

below 1.25V. It typically sinks 3.2mA with a saturation

voltage of 0.1V. With PFI above 1.25V, PFO is actively

pulled to VOUT. Connecting PFI through a voltage-

divider to an unregulated supply allows PFO to gener-

ate an NMI as the unregulated power begins to fall

(Figure 9b). If the unregulated supply is inaccessible,

Table 1. Input and Output States in

Battery-Backup Mode

PIN

NAME

STATUS

1

VBATT Supply current is 1µA maximum.

2

VOUT

VOUT is connected to VBATT through

an internal PMOS switch.

3

VCC

Battery-switchover comparator

monitors VCC for active switchover.

4

GND

GND—0V reference for all signals.

5

BATT ON

Logic high. The open-circuit output is

equal to VOUT.

The power-fail comparator remains

6

–——–

PFO

active in the battery-backup mode for

VCC ≥ VB–—A—T–T - 1.2V typ. Below this

voltage, PFO is forced low.

The power-fail comparator remains

7

PFI

active in the battery-backup mode for

VCC ≥ VBATT - 1.2V typ.

8

SWT

SWT is ignored.

9

–M—R–

M–—R– is ignored.

–——————–

10 LOWLINE Logic low*

11

WDI

WDI is ignored, and goes high

impedance.

12

–—–

CE OUT

Logic high. The open-circuit output

voltage is equal to VOUT.

–—–

13

CE IN High impedance

14

–——–

WDO

Logic high. The open-circuit output

voltage is equal to VOUT.

–————–

15

RESET Logic low*

16

–———–

WDPO

Logic high. The open-circuit output

voltage is equal to VOUT.

* VCC must be below the reset threshold to enter battery-

backup mode.

use LOWLINE to generate the NMI. The LOWLINE

threshold is typically 150mV above the reset threshold

(see LOWLINE Output section).

Battery-Backup Mode

The MAX791 requires two conditions to switch to bat-

tery-backup mode: 1) VCC must be below the reset

threshold; 2) VCC must be below VBATT. Table 1 lists

the status of the inputs and outputs in battery-backup

mode.

12 ______________________________________________________________________________________

Share Link: