Mic ro p ro c e s s o r S u p e rvis o ry Circ u it s
1693L/AX80M
+5V
+5V
V
CC
V
CC
VBATT
VBATT
2.8V
MAX691A
MAX693A
MAX800L
MAX800M
MAX691A
MAX693A
MAX800L
MAX800M
2.0V to 5.5V
PFI
LOW BATT
PFO
CE OUT
CE IN
50Ω
OUTPUT
GND
GND
C
LOAD
IMPEDANCE
Figure 6. CE Propagation Delay Test Circuit
Figure 7. Low-Battery Indicator
Power-Fail Output
Table 2. Input and Output Status in Battery-Backup
Mode
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
PIN
NAME
STATUS
1
VBATT
Supply current is 1µA max.
pulled to VOUT
.
V
is connected to VBATT through an
OUT
2
V
OUT
Ba t t e ry-Ba c k u p Mo d e
internal PMOS switch.
Two conditions are required to switch to battery-back-
up mode: 1) VCC must be below the reset threshold,
and 2) VCC must be below VBATT. Table 2 lists the sta-
tus of the inputs and outputs in battery-backup mode.
Battery switchover comparator monitors
3
4
5
V
CC
V
CC
for active switchover.
GND
GND 0V, 0V reference for all signals.
Logic high. The open-circuit output is
Ba t t e ry On Ou t p u t
The Battery On (BATT ON) output indicates the status
of the inte rna l VCC/b a tte ry-s witc hove r c omp a ra tor,
which controls the internal VCC and VBATT switches.
For VCC greater than VBATT (ignoring the small hys-
teresis effect), BATT ON typically sinks 3.2mA at 0.1V
saturation voltage. In battery-backup mode, this termi-
nal sources approximately 10µA from VOUT. Use BATT
ON to indicate battery-switchover status or to supply
base drive to an external pass transistor for higher-cur-
rent applications (see Typical Operating Circuit).
BATT ON
equal to V
.
OUT
6
7
8
Logic low*
OSC IN is ignored.
LOWLINE
OSC IN
OSC SEL OSC SEL is ignored.
The power-fail comparator remains
9
PFI
active in the battery-backup mode for
≥ VBATT - 1.2V typ.
V
CC
The power-fail comparator remains
active in the battery-backup mode for
10
PFO
V
CC
≥ VBATT - 1.2V typ. Below this volt-
In p u t S u p p ly Vo lt a g e
The Input Supply Voltage (VCC) should be a regulated
5V. VCC connects to VOUT via a parallel diode and a
large PMOS switch. The switch carries the entire cur-
rent load for currents less than 250mA. The parallel
diode carries any current in excess of 250mA. Both the
switch and the diode have impedances less than 1Ω
each. The maximum continuous current is 250mA, but
power-on transients may reach a maximum of 1A.
age, PFO is forced low.
11
12
13
14
WDI
CE OUT
CE IN
Watchdog is ignored.
Logic high. The open-circuit voltage is
equal to V
.
OUT
High impedance
Logic high. The open-circuit voltage is
WDO
equal to V
.
OUT
15
16
Logic low*
High impedance*
RESET
RESET
* V must be below the reset threshold to enter battery-backup
CC
mode.
______________________________________________________________________________________ 11
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
