MAX690TC/D Maxim Integrated, MAX690TC/D Datasheet - Page 8
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MAX690TC/D
Manufacturer Part Number
MAX690TC/D
Description
Supervisory Circuits 3.0V/3.3V Microprocessor Supervisory Circuit with Reset Threshold of 3.075V
Manufacturer
Maxim Integrated
Series
MAX690R, MAX690S, MAX690T, MAX704R, MAX704S, MAX704T, MAX802, MAX802R, MAX802S, MAX802T, MAX804, MAX804R, MAX804S, MAX804T, MAX805, MAX805R, MAX805S, MAX805T, MAX806, MAX806R, MAX806S, MAX806Tr
Datasheet
1.MAX805TEPA.pdf
(12 pages)
Specifications of MAX690TC/D
Number Of Voltages Monitored
1
Monitored Voltage
4.65 V
Output Type
Active Low, Push-Pull
Manual Reset
Not Resettable
Watchdog
Watchdog
Battery Backup Switching
Backup
Supply Voltage - Max
5.5 V
Chip Enable Signals
No
Power Fail Detection
Yes
Supply Current (typ)
350 uA
Supply Voltage - Min
1 V
In the event of a brownout or power failure, it may be
necessary to preserve the contents of RAM. With a
backup battery installed at VBATT, the devices auto-
matically switch RAM to backup power when V
falls.
This family of µP supervisors (designed for 3.3V and 3V
systems) doesn’t always connect VBATT to V
VBATT is greater than V
(through a 140Ω switch) when V
VBATT is greater than V
1.75V (typ) regardless of the VBATT voltage. This is
done to allow the backup battery (e.g., a 3.6V lithium
cell) to have a higher voltage than V
Switchover at V
mode is entered before V
minimum required to reliably retain data in CMOS RAM.
Switchover at higher V
backup-battery life. When V
deferred until V
(V
V
A logic low on
while
high. This input has an internal 70µA pull-up current, so
it can be left open if it is not used.
TTL or CMOS logic levels, or with open-drain/collector
outputs. Connect a normally open momentary switch
from
external debounce circuitry is not required.
3.0V/3.3V Microprocessor Supervisory Circuits
Table 1. Input and Output Status in
Battery-Backup Mode
8
PIN NAME
CC
RST
–
R
—
RESET
VBATT
V
–
P
WDI
E
_______________________________________________________________________________________
V
—
–
M
—
PFI
OUT
through a 3Ω PMOS power switch.
F
—
CC
—
S
) to ensure a stable supply. V
—
–
M
–
M
R
O
–
—
E
—
–
—
R
R
T
–
–
–
to GND to create a manual-reset function;
is low, and for t
Connected to VBATT through an internal
140Ω switch
Disconnected from V
The power-fail comparator is disabled when
V
Logic low when V
The watchdog timer is disabled
Disabled
Low logic
High impedance
Connected to V
CC
–
M
—
SW
< V
R
–
CC
asserts reset. Reset remains asserted
(2.40V) ensures that battery-backup
SW
Backup-Battery Switchover
rises above the reset threshold
CC
CC
OUT
OUT
CC
WP
CC
. VBATT connects to V
, or when V
voltages would decrease
CC
STATUS
gets too close to the 2.0V
< V
(200ms) after
OUT
recovers, switchover is
–
M
SW
CC
—
R
OUT
CC
–
or PFI < V
is below V
can be driven with
Manual Reset
.
is connected to
CC
falls below
–
M
—
PFT
OUT
R
–
SW
returns
when
and
OUT
CC
These µP supervisory circuits are not short-circuit
protected. Shorting V
up transients such as charging a decoupling
capacitor—destroys the device. Decouple both V
and VBATT pins to ground by placing 0.1µF capacitors
as close to the device as possible.
SuperCaps™ are capacitors with extremely high
capacitance values (e.g., order of 0.47F) for their size.
Figure 3 shows two ways to use a SuperCap as a
backup power source. The SuperCap may be
connected through a diode to the 3V input (Figure 3a)
or, if a 5V supply is also available, the SuperCap may
be charged up to the 5V supply (Figure 3b) allowing a
longer backup period. Since VBATT can exceed V
while V
special precautions when using these µP supervisors
with a SuperCap.
These µP supervisors were designed for battery-
backed applications. If a backup battery is not used,
connect both VBATT and V
different µP supervisor such as the MAX706T/S/R or
MAX708T/S/R.
The backup power source can be removed while V
remains valid, if VBATT is decoupled with a 0.1µF
capacitor to ground, without danger of triggering
RESET/
battery-backup mode cannot be entered.
The power-fail comparator has a typical input
hysteresis of 10mV. This is sufficient for most applica-
tions where a power-supply line is being monitored
through an external voltage divider (see the Monitoring
an Additional Power Supply section).
If additional noise margin is desired, connect a resistor
between
the ratio of R1 and R2 such that PFI sees 1.237V (V
when V
hysteresis and will typically be more than 10 times the
value of R1 or R2. The hysteresis window extends both
above (V
SuperCap is a trademark of Baknor Industries.
__________Applications Information
CC
–
IN
R
—
H
–
P
—
E
) and below (V
—
falls to its trip point (V
F
is above the reset threshold, there are no
—
S
—
O
–
E
—
T
and PFI as shown in Figure 4a. Select
–
Replacing the Backup Battery
. As long as V
to the Power-Fail Comparator
Operation without a Backup
as a Backup Power Source
OUT
L
) the original trip point (V
to ground—excluding power-
OUT
Adding Hysteresis
Using a SuperCap
CC
TRIP
stays above V
to V
Power Source
). R3 adds the
CC
, or use a
TRIP
PFT
SW
CC
CC
CC
).
)
,