Datasheet

BATTON Indicator
(MAX16035/MAX16039 Only)
BATTON is a push-pull output that asserts high when in
battery-backup mode. BATTON typically sinks 3.2mA at
a 0.4V saturation voltage. In battery-backup mode, this
terminal sources approximately 10μA from OUT. Use
BATTON to indicate battery-switchover status or to supply
base drive to an external pass transistor for higher current
applications (Figure 3).
RESETIN Comparator
(MAX16036/MAX16040 Only)
An internal 1.235V reference sets the RESETIN threshold
voltage. RESET asserts when the voltage at RESETIN is
below 1.235V. Use the RESETIN function to monitor a
secondary power supply.
Use the following equations to set the reset threshold volt-
age (V
RTH
) of the secondary power supply (see Figure 4):
V
RTH
= V
REF
(R1/R2 + 1)
where V
REF
= 1.235V. To simplify the resistor selection,
choose a value for R2 and calculate R1:
R1 = R2 [(V
RTH
/V
REF
) - 1]
Since the input current at RESETIN is 25nA (max), large
values (up to 1MΩ) can be used for R2 with no significant
loss in accuracy.
Power-Fail Comparator
The MAX16033–MAX16040 issue an interrupt (nonmask-
able or regular) to the μP when a power failure occurs.
The power line is monitored by two external resistors
connected to the power-fail input (PFI). When the voltage
at PFI falls below 1.235V, the power-fail output (PFO)
drives the processor’s NMI input low. An earlier power-fail
warning can be generated if the unregulated DC input of
the regulator is available for monitoring. The MAX16033–
MAX16040 turn off the power-fail comparator and force
PFO low when V
CC
falls below the reset threshold voltage
(Figure 1). The MAX160_ _L devices provide push-pull
PFO outputs. The MAX160_ _P devices provide open-
drain PFO outputs.
Figure 4. Setting RESETIN Voltage for the MAX16036/
MAX16040
Figure 3. MAX16035/MAX16039 BATTON Driving an External Pass Transistor
MAX16036
MAX16040
R1
RESETIN
V
IN
V
CC
R2
2.4V TO 5.5V
CE
(CEIN)
( ) FOR MAX16035 ONLY
A0–A15
µP
CMOS RAM
BATTON
V
CC
BATT
(CEOUT)
GND
RESET
OUT
0.1µF
ADDRESS
DECODE
MAX16035
MAX16039
RESET
MAX16033–MAX16040 Low-Power Battery-Backup
Circuits in Small μDFN Packages
www.maximintegrated.com
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