Rainbow Electronics MAX16021 - Manual (Page 16)

MAX16016/MAX16020/MAX16021
Low-Power µP Supervisory Circuits with
Battery-Backup Circuit and Chip-Enable Gating
16 ______________________________________________________________________________________
To reenable the freshness seal:
1) Connect a battery to BATT.
2) Bring V CC to 0V.
3) Drive MR higher than V BATT + 1.2V for at least 3µs.
4) Pull OUT to 0V.
Reset Output
A µP’s reset input starts the µP in a known state. The
µP supervisory circuits assert a reset to prevent code-
execution errors during power-up, power-down, and
brownout conditions. Reset output is guaranteed to be
a logic-low or logic-high depending on the device cho-
sen. RESET or RESET asserts when V
CC
is below the
reset threshold and remains asserted for at least 145ms
(t
RP ) after V CC rises above the reset threshold. RESET
or RESET also asserts when MR is low. The MAX16016
watchdog function causes RESET to assert in pulses
following a watchdog timeout. The reset output is avail-
able in both push-pull and open-drain configurations.
Power-Fail Comparator
The MAX16016/MAX16020/MAX16021 offer an under-
voltage comparator that the output PFO goes low when
the voltage at PFI falls below its V
PFT threshold.
Common uses for the power-fail comparator include
monitoring the power supply (such as a battery) before
any voltage regulation to provide an early power-fail
warning, so software can conduct an orderly system
shutdown. The power-fail comparator has a typical
input hysteresis of V
PFT-HYS and is powered from OUT,
making it independent of the reset circuit. Connect the
PFI input to GND if not used.
Applications Information
Monitoring an Additional Supply
The MAX16016/MAX16020/MAX16021 µP supervisors
can monitor either positive or negative supplies using a
resistive voltage-divider to PFI. PFO can be used to
generate an interrupt to the µP or to trigger a reset
(Figures 2 and 3). To monitor a negative supply, con-
nect the top of the resistive divider to V
CC . Connect the
bottom of the resistive divider to the negative voltage to
be monitored.
MAX16016L
MAX16020L
MAX16021L
RESET RESET
PFO
MR
µP
GND
ADDITIONAL SUPPLY RESET VOLTAGE
R1+R2
R2
V
2(RESET)
= V
PFT
x
(—)
V
CC
PFI
0.1 µF
V 1
R2
R1
V 2
Figure 2. Monitoring an Additional Supply by Connecting PFO
to MR
MAX16016
MAX16020
MAX16021
PFO
PFO
GND
R2
R1
V TRIP = V PFT -
—
(5 - V PFT )
V
TRIP
IS NEGATIVE
V CC
PFI
0.1 µF
R2
R1
5V
V-
0
+5V
V TRIP V- 0V
Figure 3. Monitoring a Negative Supply