3 .0 V/3 .3 V Ad ju s t a b le Mic ro p ro c e s s o r
S u p e rvis o ry Circ u it s
PMOS FET
BODY DIODE
TO CMOS RAM
3.0V OR 3.3V
S
D
G
V
CC
BATT ON OUT
V
CC
BATT ON OUT
MAX793
MAX794
MAX795
MAX793
MAX794
MAX795
GND
GND
(a)
(b)
Figure 14. Driving an External Transistor with BATT ON
3.0V OR 3.3V
+5V
3.0V OR
3.3V
V
MAX793
MAX794
OUT
TO STATIC
RAM
CC
V
MAX793
MAX794
OUT
TO STATIC
RAM
CC
CC
34/MAX795
V
V
CC
1N4148
1N4148
0.47F
BATT
RESET
TO µP
BATT
RESET
TO µP
0.47F
GND
GND
(a)
Figure 15. Using a SuperCap™ as a Backup Source
(b)
The IC decides whether or not to enter freshness seal
mode during all reset timeout periods. During a power-
____________________________Erra t u m
Initial versions of the MAX793 and MAX794 have a
logic design error that can cause the loss of output volt-
up reset timeout period (which occurs when V
is
CC
raised above the MAX793’s reset threshold or the volt-
age on the MAX794’s RESET IN pin is raised above the
RESET IN threshold), the IC momentarily disconnects
the PFO pin from the comparator output and lightly
age (OUT) when V
is absent even though a backup
CC
battery is connected to the BATT input. Applications
that do not use the MR input (including all MAX795
a p p lic a tions ) a re una ffe c te d b y this p he nome non.
Also, applications that do not use PFO are unaffected if
pulls PFO up to V . The voltage level on the PFO pin
CC
is then tested and, if it is low, freshness seal mode is
chosen. (PFO is reconnected to the comparator output
before the end of the reset timeout period.)
PFI is tied to V
.
CC
The loss of output voltage is caused by the IC incor-
re c tly e nte ring the b a tte ry “fre s hne s s s e a l” mod e .
Normally, freshness seal mode is activated by ground-
ing PFO during a power-up reset timeout period. Then,
However, when a reset is initiated by MR, the PFO pin
incorrectly remains connected to the comparator output
during the entire timeout period and is not pulled up. If
the comparator is driving PFO low during an MR reset
the removal of V
powers the IC down without con-
CC
necting the backup battery to OUT.
16 ______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
