MAX793_CSE データシートの表示（PDF） - Maxim Integrated

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MAX793_CSE

3.0V/3.3V Adjustable Microprocessor Supervisory Circuits

Maxim Integrated 

3.0V/3.3V Adjustable Microprocessor

Supervisory Circuits

VIN

R1

R2

PFI

R3

VCC

MAX793

MAX794

C1*

PFO

GND

TO µP

*OPTIONAL

VIN

R1

R2

PFI

R3

VCC

MAX793

MAX794

C1*

PFO

GND

TO µP

*OPTIONAL

PFO

0V

0V

VL

VH

VIN

VTRIP

( ) VTRIP = VPFT

R1 + R2

R2

WHERE VPFT = 1.237V

( ) VH = (VPFT + VPFH) (R1)

1

+

1

1

+

R1 R2 R3

VPFH = 10mV

( ) VL = R1 VPFT

111

++

– VCC

R1 R2 R3 R3

(a)

PFO

0V

0V

VTRIP

VH

VIN

( ) R1 + R2

VTRIP = VPFT R2

( ) VH = R1 (VPFT + VPFH)

111

++

R1 R2 R3

– VD

R3

WHERE VPFT = 1.237V

VPFH = 10mV

VD = DIODE FORWARD VOLTAGE DROP

(b)

VL = VTRIP

Figure 16. Adding Hysteresis to the Power-Fail Comparator: (a) Symmetrical Hysteresis, (b) Hysteresis Only on Rising VIN

timeout period (because PFI is below the PFI thresh-

old), the IC will test the voltage level on PFO, find that it

is low, and incorrectly decide to enter freshness seal

mode. If VCC is later removed, the backup battery will

not be connected to OUT and any devices powered by

OUT will lose power.

Applications that do not use the PFO comparator need

not be affected by this problem. Simply connect PFI to

VCC and PFO will be driven high during all reset time-

out periods. Freshness seal mode can be entered only

when PFO is low.

The IC is under revision to correct this problem. The

revised IC will disable PFO during all reset timeout peri-

ods including MR-initiated ones. This revision will not

affect applications that either do not use MR or do not

use PFO, but could affect applications that require the

use of the PFO output during MR-initiated reset timeout

periods. The revised ICs are expected to be available

in late 1996. For technical assistance, please contact

Maxim Applications at 1-800-998-8800 or at

http:// www. maxim-ic.com.

VCC

VCC

RESET

GENERATOR

RESET

N

MAX793

MAX794

MAX795

GND

VCC

RESET

µP

GND

Figure 17. Interfacing to µPs with Bidirectional Reset I/O

______________________________________________________________________________________ 17

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