MAX16033 Datasheet, PDF (11/21 Pages) Maxim Integrated Products – Low-Power Battery Backup Circuits in Small μDFN Packages

Low-Power Battery Backup
Circuits in Small µDFN Packages
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 (see Figure 3).
RESETIN Comparator
(MAX16036/MAX16040 Only)
An internal 1.235V reference sets the RESETIN thresh-
old 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
voltage (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 signifi-
cant 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 con-
nected 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 warn-
ing 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 volt-
age (see Figure 1). The MAX160_ _L devices provide
push-pull PFO outputs. The MAX160_ _P devices provide
open-drain PFO outputs.
V_CC
V_IN
R1
R2
MAX16036
MAX16040
RESETIN
Figure 4. Setting RESETIN Voltage for the
MAX16036/MAX16040
2.4V TO 5.5V
0.1µF
V_CC
BATT
BATTON
OUT
(CEOUT)
CE
CMOS RAM
MAX16035
MAX16039
(CEIN)
ADDRESS
DECODE
A0–A15
µP
GND
( ) FOR MAX16035 ONLY
RESET
RESET
Figure 3. MAX16035/MAX16039 BATTON Driving an External Pass Transistor
______________________________________________________________________________________ 11