MAX6909EO33 Maxim Integrated, MAX6909EO33 Datasheet - Page 29

• Manufacturer Part Number: MAX6909EO33
• Description: Real Time Clock
• Manufacturer: Maxim Integrated
• Series: MAX6909, MAX6910r

Specifications of MAX6909EO33

• Function: Clock, Calendar, Watchdog Timekeeper, NV SRAM Control
• Rtc Bus Interface: Serial
• Time Format: HH
• Rtc Memory Size: 31 B
• Supply Voltage - Max: 3.6 V
• Supply Voltage - Min: 3 V
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Package / Case: QSOP-20

Figure 26. Using the Power-Fail Comparator to Monitor Additional Power Supplies
PFO can be connected to MR so that a low voltage on
PFI activates RESET and RESET (Figure 26). In this
configuration, when the monitored voltage causes PFI
to fall below V
be asserted. A 200ms reset is generated, during which
PFO is forced high and MR is released. At the end of
the 200ms reset, the power-fail comparator reflects the
state of PFI, which if below V
Monitoring Additional Power Supplies
PFO
V
CC
V
V
NOTE: V
PFT
TRIP
L
I
R1
R2
= R2 x V
Applications Information
a) MONITORING A NEGATIVE SUPPLY
= R2 x (V
2
, PFO pulls MR low, causing a reset to
V
______________________________________________________________________________________
IN
TRIP
C-Compatible Real-Time Clocks with µP
PFT
AND V
PFT
PFO IS ACTIVE HIGH WHEN
MONITORING A NEGATIVE SUPPLY
x
(
+ V
L
R1
1
ARE NEGATIVE.
PFH
+
V
PFT
)
R2
L
1
x
PFI
PFO
(
)
, causes another reset.
R1
-
Supervisor and NV RAM Controller
1
V
MAX6909/
R1
MAX6910
CC
+
R2
GND
1
V
CC
V
)
TRIP
-
V
R1
CC
0V
V
IN
The power-fail comparator has a typical input hystere-
sis of 30mV. This is sufficient for most applications
where a power-supply line is being monitored through
an external voltage-divider supply (Figure 27).
If additional noise margin is desired, connect a resistor
between PFO and PFI (Figure 27(a)). Select the ratio of
R1 and R2 such that PFI sees V
trip point (V
should typically be more than 10 times the value of R1
or R2. The hysteresis window extends both above (V
and below (V
PFO
V
R1
R2
CC
V
IN
TRIP
V
V
H
TRIP
b) MONITORING SECONDARY SUPPLY
L
=
) the original trip point (V
(V
= V
). R3 adds the additional hysteresis and
PFT
PFT
+ V
x R1 + R2
PFH
PFI
PFO
(
)
V
Adding Hysteresis to the
R2
x R1 + R2
TRIP
MAX6909/
MAX6910
(
Power-Fail Comparator
GND
)
V
R2
CC
)
PFT
MR
when V
V
TRIP
IN
).
IN
V
falls to its
IN
29
H
)