MAX793 Maxim, MAX793 Datasheet - Page 8

• Manufacturer Part Number: MAX793
• Description: 3.0V/3.3V Adjustable Microprocessor Supervisory Circuits
• Manufacturer: Maxim

3.0V/3.3V Adjustable Microprocessor
Supervisory Circuits
The MAX793/MAX794/MAX795 are designed for 3.3V
and 3V systems, and provide a number of supervisory
functions (see the Selector Guide on the front page).
Figures 1 and 2 show the typical timing relationships of
the various outputs during power-up and power-down
with typical V
Many microprocessor-based products require manual-
reset capability, allowing the operator, a test technician,
or external logic circuitry to initiate a reset. On the
MAX793/MAX794, a logic low on MR asserts reset. Reset
remains asserted while MR is low, and for t
after it returns high. During the first half of the reset time-
Figure 1. Timing Diagram, V
8
_______________Detailed Description
_______________________________________________________________________________________
Manual Reset Input (MAX793/MAX794)
V
V
V
V
(MAX793/MAX794)
V
(MAX793)
PFO
(MAX793/MAX794)
BATT ON
SHOWN FOR V
TYPICAL PROPAGATION DELAYS REFLECT A 40mV OVERDRIVE.
V
V
MAX794: V
RESET
CC
CE OUT
WDO
BOK
LOWLINE
RESET
(MAX793/MAX794)
(PULLED UP TO V
(MAX793/MAX794)
CC
RESET IN
CC
General Timing Characteristics
rise and fall times.
= 0V to 3.3V, V
= V
CC
CC
(V
)
RST IN
CC
BATT
V
/ V
BATT
Rising
= 3.6V, CE IN = GND.
RST
)
V
RP
SW
(200ms)
25 s
25 s
25 s
V
RST
V
LL
25 s
out period (t
nally forced low, to facilitate enabling the battery fresh-
ness seal. MR has an internal 70µA pull-up current, so it
can be left open if it is not used. This input can be driven
with TTL- or CMOS-logic levels, or with open-drain/collec-
tor outputs. Connect a normally open momentary switch
from MR to GND to create a manual-reset function; exter-
nal debounce circuitry is not required. If MR is driven
from long cables or the device is used in a noisy environ-
ment, connect a 0.1µF capacitor from MR to ground to
provide additional noise immunity.
A microprocessor’s (µP’s) reset input starts the µP in a
known state. These MAX793/MAX794/MAX795 µP
supervisory circuits assert a reset to prevent code exe-
cution errors during power-up, power-down, and
5 s
t
t
RP
RP
/
/
2
2
RP
), the state of MR is ignored if PFO is exter-
t
t
RP
RP
(PFO FOLLOWS PFI)
Reset Outputs