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MAX6361LUT31-T-MAX6363HUT44-T-MAX6363LUT29-T-MAX6363LUT31-T
2.38 V, SOT23, low-power, mP supervisory circuit with battery backup
General DescriptionThe MAX6361–MAX6364 supervisory circuits reduce the
complexity and number of components required for
power-supply monitoring and battery control functions in
microprocessor (µP) systems. The circuits significantly
improve system reliability and accuracy compared to that
obtainable with separate ICs or discrete components.
Their functions include µP reset, backup battery
switchover, and power failure warning.
The MAX6361–MAX6364 operate from supply voltages as
low as +1.2V. The factory-preset reset threshold voltage
ranges from 2.32V to 4.63V (see Ordering Information).
These devices provide a manual reset input (MAX6361),
watchdog timer input (MAX6362), battery-on output
(MAX6363), and an auxiliary adjustable reset input
(MAX6364). In addition, each part type is offered in three
reset output versions: an active-low push-pull reset, an
active-low open-drain reset, and an active-high open-
drain reset (see Selector Guide at end of data sheet).
Applications
FeaturesLow +1.2V Operating Supply Voltage
(VCCor VBATT)Precision Monitoring of +5.0V, +3.3V, +3.0V, and
+2.5V Power-Supply VoltagesDebounced Manual Reset Input (MAX6361)Watchdog Timer with 1.6s Timeout Period
(MAX6362)Battery-On Output Indicator (MAX6363)Auxiliary User-Adjustable RESET IN (MAX6364)Three Available Output Structures
Push-Pull RESET, Open-Drain RESET,
Open-Drain RESETRESET/RESET Valid Down to 1.2V Guaranteed
(VCCor VBATT)Power-Supply Transient Immunity150ms (min) Reset Timeout PeriodSmall 6-Pin SOT23 Package
MAX6361–MAX6364
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup19-1615; Rev 2; 7/00
Ordering Information
Pin Configurations
Note:These parts offer a choice of reset threshold voltages.
From the table below, select the suffix corresponding to the
desired thresholdvoltage and insert it into the part number to
complete it. When ordering from the factory, there is a 2500-
piece minimum on the SOT package (tape-and-reel only).
Selector Guide appears at end of data sheet.
Typical Operating Circuit appears at end of data sheet.
MAX6361–MAX6364
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= +2.4V to +5.5V, VBATT= 3V, TA= -40°C to +85°C, reset not asserted. Typical values are at TA= +25°C, unless otherwise
noted.) (Note 1)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Terminal Voltages (with respect to GND)
VCC, BATT, OUT.......................................................-0.3V to +6V
RESET(open drain), RESET (open drain)................-0.3V to +6V
BATT ON, RESET (push-pull), RESET IN,
WDI.......................................................-0.3V to (VOUT+ 0.3V).............................................................-0.3V to (VCC+ 0.3V)
Input Current
VCCPeak ............................................................................1A
VCCContinuous............................................................250mA
BATT Peak....................................................................250mA
BATT Continuous............................................................40mA
GND................................................................................75mA
Output Current
OUT................................Short-Circuit Protection for up to 10s
RESET, RESET, BATT ON ..............................................20mA
Continuous Power Dissipation (TA= +70°C)
6-Pin SOT23 (derate 8.70mW/°C above +70°C) .........696mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
MAX6361–MAX6364
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup
ELECTRICAL CHARACTERISTICS (continued)(VCC= +2.4V to +5.5V, VBATT= 3V, TA= -40°C to +85°C, reset not asserted. Typical values are at TA= +25°C, unless otherwise
noted.) (Note 1)
Note 1:All devices are 100% production tested at TA= +25°C. Limits over temperature are guaranteed by design.
Note 2:VBATTcan be 0 anytime or VCCcan go down to 0 if VBATTis active (except at startup).
MAX6361–MAX6364
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup
Typical Operating Characteristics(TA= +25°C, unless otherwise noted.)
MAX6361–MAX6364
SOT23, Low-Power µP Supervisory Circuits
with Battery BackupMAX6364
RESET IN THRESHOLD
vs. TEMPERATURE
MAX6361 toc10
TEMPERATURE (°C)
THRESHOLD (V)
Typical Operating Characteristics (continued)
(TA= +25°C, unless otherwise noted.)
Pin Description
MAX6361–MAX6364
Detailed DescriptionThe Typical Operating Circuitshows a typical connection
for the MAX6361–MAX6364 family. OUT powers the stat-
ic random-access memory (SRAM). OUT is internally
connected to VCCif VCCis greater than the reset thresh-
old, or to the greater of VCCor VBATTwhen VCCis less
than the reset threshold. OUT can supply up to 150mA
from VCC. When VCCis higher than VBATT, the BATT ON
(MAX6363) output is low. When VCCis lower than VBATT,
an internal MOSFET connects the backup battery to
OUT. The on-resistance of the MOSFET is a function of
backup-battery voltage and is shown in the Battery to
Out On-Resistance vs. Temperature graph in the Typical
Operating Characteristicssection.
Backup-Battery Switchover In a brownout or power failure, it may be necessary to
preserve the contents of the RAM. With a backup bat-
tery installed at BATT, the MAX6361–MAX6364 auto-
matically switch the RAM to backup power when VCC
falls. The MAX6363 has a BATT ON output that goes
high when in battery-backup mode. These devices
require two conditions before switching to battery-
backup mode: VCCmust be below the reset threshold.VCCmust be below VBATT.
Table 1 lists the status of the inputs and outputs in bat-
tery-backup mode. The device will not power up if the
only voltage source is on BATT. OUT will only power up
from VCCat startup.
Manual Reset Input (MAX6361 Only)Many µP-based products require manual reset capabili-
ty, allowing the operator, a test technician, or external
logic circuitry to initiate a reset. For the MAX6361, a logic
low on MRasserts reset. Reset remains asserted whileMRis low, and for a minimum of 150ms (tRP) after it
returns high. MRhas an internal 20kΩpull-up resistor to
VCC. This input can be driven with TTL/CMOS logic lev-
els or with open-drain/collector outputs. Connect a nor-
mally open momentary switch from MRto GND to create
a manual reset function; external debounce circuitry is
not required. If MRis driven from long cables or the
device is used in a noisy environment, connect a 0.1µF
capacitor from MRto GND to provide additional noise
immunity.
Watchdog Input (MAX6362 Only)The watchdog monitors µP activity through the input
WDI. If the µP becomes inactive, the reset output is
asserted in pulses. To use the watchdog function, con-
nect WDI to a bus line or µP I/O line. A change of state
(high to low or low to high) within the watchdog timeout
period (tWD) with a 100ns minimum pulse width clears
the watchdog timer. If WDI remains high or low for longer
than the watchdog timeout period, the internal watchdog
timer runs out and a reset pulse is triggered for the reset
timeout period (tRP). The internal watchdog timer clears
whenever reset asserts or the WDI sees a rising or falling
edge within the watchdog timeout period. If WDI remains
in a high or low state for an extended period of time, a
reset pulse asserts after every watchdog timeout period
(tWD) (Figure 1).
Reset In (MAX6364 Only)RESET IN is compared to an internal 1.235V reference.
If the voltage at RESET IN is less than 1.235V, reset is
asserted. The RESET IN comparator may be used as
an undervoltage detector to signal a failing power sup-
ply. It can also be used as a secondary power-supply
reset monitor.
To program the reset threshold (VRTH) of the secondary
power supply, use the following equation (see Typical
Operating Circuit):
where VREF= 1.235V. To simplify the resistor selection,
choose a value for R2 and calculate R1:
Since the input current at RESET IN is 25nA (max), large
values (up to 1MΩ) can be used for R2 with no signifi-
cant loss in accuracy. For example, in the Typical
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup
