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General Description
The 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 open-drain reset, an active-low open-drain reset, and an active-high open-drain reset (see Selector Guide at end of data sheet).
Applications
Features
?Low +1.2V Operating Supply Voltage (V CC or V BATT )
?Precision Monitoring of +5.0V, +3.3V, +3.0V, and +2.5V Power-Supply Voltages
?Debounced 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 RESET
?RESET/RESET Valid Down to 1.2V Guaranteed (V CC or V BATT )
?Power-Supply Transient Immunity ?150ms (min) Reset Timeout Period ?Small 6-Pin SOT23 Package
MAX6361–MAX6364
SOT23, Low-Power μP Supervisory Circuits
with Battery Backup
________________________________________________________________Maxim Integrated Products
1
19-1615; Rev 3; 11/05
Ordering Information
Pin Configurations
From the table below, select the suffix corresponding to the desired threshold voltage 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).
Devices are available in both leaded and lead-free packaging.Specify lead-free by replacing "-T" with "+T" when ordering.
Computers Controllers
Intelligent Instruments Critical μP/μC Power Monitoring
Fax Machines Industrial Control POS Equipment
Portable/Battery-Powered Equipment
Selector Guide appears at end of data sheet.
Typical Operating Circuit appears at end of data sheet.
M A X 6361–M A X 6364
SOT23, Low-Power μP Supervisory Circuits with Battery Backup
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V CC = +2.4V to +5.5V, V BATT = 3V, T A = -40°C to +85°C, reset not asserted. Typical values are at T A = +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)
V CC , 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 (V OUT + 0.3V)MR .............................................................-0.3V to (V CC + 0.3V)Input Current
V CC Peak ............................................................................1A V CC Continuous............................................................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 (T A = +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
_______________________________________________________________________________________3
ELECTRICAL CHARACTERISTICS (continued)
(V CC = +2.4V to +5.5V, V BATT = 3V, T A = -40°C to +85°C, reset not asserted. Typical values are at T A = +25°C, unless otherwise noted.) (Note 1)
Note 1:All devices are 100% production tested at T A = +25°C. Limits over temperature are guaranteed by design.Note 2:V BATT can be 0 anytime or V CC can go down to 0 if V BATT is active (except at startup).
M A X 6361–M A X 6364
SOT23, Low-Power μP Supervisory Circuits with Battery Backup 4_______________________________________________________________________________________
Typical Operating Characteristics
(T A = +25°C, unless otherwise noted.)
12
14
16
18
20SUPPLY CURRENT vs. TEMPERATURE
(NO LOAD)
TEMPERATURE (°C)
S U P P L Y C U R R E N T (μA )
-40
20
40
-20
60
80
0.20.6
0.40.81.01.2BATTERY SUPPLY CURRENT (BACKUP MODE) vs. TEMPERATURE
TEMPERATURE (°C)B A T T E R Y S U P P L Y C U R R E N T (μA )
-402040-2006080
14325
67BATTERY TO OUT ON-RESISTANCE
vs. TEMPERATURE
TEMPERATURE (°C)
B A T T T O O U T O N -R E S I S T A N
C E (?)
-40
20
40
-20
60
80
00.3
0.9
0.6
1.2V CC TO OUT ON-RESISTANCE
vs. TEMPERATURE
TEMPERATURE (°C)
V O U T T O O U T O N -R E S I S T A N C E (?)
-40
20
40
-20
60
80
190
195
205
200
210
RESET TIMEOUT PERIOD vs. TEMPERATURE
M A X 6361 t o c 05
TEMPERATURE (°C)
R E S E T T I M E O U T P E R I O D (m s )
-40
20
40
-20
60
80
3015
756045135
12010590V CC TO RESET PROPAGATION DELAY
vs. TEMPERATURE
TEMPERATURE (°C)
P R O P A G A T I O N D E L
A Y (μs )-40
20
40
-20
60
80
2.03.0
2.55.0
4.54.03.5RESET THRESHOLD vs. TEMPERATURE
TEMPERATURE (°C)
T H R E S H O L D (V )
-40
20
40
-20
60
80
1.21.41.31.61.51.91.81.7
2.0-40
-20
20
40
60
80
MAX6362
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
M A X 6361t o c 06a
TEMPERATURE (°C)
W A T C H D O G T I M E O U T P E R I O D (s )
1
100
10
1k
10k
MAXIMUM TRANSIENT DURATION vs. RESET THRESHOLD OVERDRIVE
RESET THRESHOLD OVERDRIVE V TH - V CC (mV)M A X I M U M T R A N S I E N T D U R A T I O N (μs )
400
300350250
200050150100
MAX6361–MAX6364
SOT23, Low-Power μP Supervisory Circuits
with Battery Backup
1.234
1.235
1.236
MAX6364
RESET IN THRESHOLD vs. TEMPERATURE
M A X 6361 t o c 10
TEMPERATURE (°C)
T H R E S H O L D (V )
-40
20
40
-20
60
80
Typical Operating Characteristics (continued)
(T A = +25°C, unless otherwise noted.)
1.01.91.61.3
2.82.52.2MAX6364
RESET IN TO RESET PROPAGATION DELAY
vs. TEMPERATURE
TEMPERATURE (°C)
P R O P A G A T I O N D E L A Y (μs )
-40
20
40
-20
60
80
Pin Description
032145678910
1
23
4
BATTERY SUPPLY CURRENT vs. SUPPLY VOLTAGE
V CC (V)
B A T T E R Y S U P P L Y
C U R R E N T (μA )
M A X 6361–M A X 6364
Detailed Description
The Typical Operating Circuit shows a typical connection for the MAX6361–MAX6364 family. OUT powers the stat-ic random-access memory (SRAM). OUT is internally connected to V CC if V CC is greater than the reset thresh-old, or to the greater of V CC or V BATT when V CC is less than the reset threshold. OUT can supply up to 150mA from V CC . When V CC is higher than V BATT , the BATT ON (MAX6363) output is low. When V CC is lower than V BATT ,an internal MOSF ET 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 Characteristics section.
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 V CC 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:
1)V CC must be below the reset threshold.2)V CC must be below V BATT .
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 V CC at 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 MR asserts reset. Reset remains asserted while MR is low, and for a minimum of 150ms (t RP ) after it returns high. MR has an internal 20k ?pull-up resistor to V CC . 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 MR to GND to create a manual reset function; external debounce circuitry is not required. If MR is driven from long cables or the device is used in a noisy environment, connect a 0.1μF capacitor from MR to 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 (t WD ) 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 (t RP ). 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 (t WD ) (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 (V RTH ) of the secondary power supply, use the following equation (see Typical Operating Circuit ):
where V REF = 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 1M ?) can be used for R2 with no signifi-cant loss in accuracy. F or example, in the Typical
SOT23, Low-Power μP Supervisory Circuits with Battery Backup 6
_______________________________________________________________________________________
R R V V RTH REF 12
1 /
=()?[]
MAX6361–MAX6364
SOT23, Low-Power μP Supervisory Circuits
with Battery Backup
_______________________________________________________________________________________
7
Operating Circuit,the MAX6362 monitors two supply voltages. To monitor the secondary 5V logic or analog supply with a 4.60V nominal programmed reset thresh-old, choose R2 = 100k ?, and calculate R1 = 273k ?.
Reset Output
A μP’s reset input starts the μP in a known state. The MAX6361–MAX6364 μP supervisory circuits assert a reset to prevent code-execution errors during power-up, power-down, and brownout conditions. RESET is guaranteed to be a logic low or high depending on the device chosen (see Ordering Information ). RESET or RESET asserts when V CC is below the reset threshold and for at least 150ms (t RP ) after V CC rises above the reset threshold. RESET or RESET also asserts when MR is low (MAX6361) and when RESET IN is less than 1.235V (MAX6364). The MAX6362 watchdog function will cause RESET (or RESET ) to assert in pulses follow-ing a watchdog timeout (Figure 1).
Applications Information
Operation Without a Backup
Power Source
The MAX6361–MAX6364 were designed for battery-backed applications. If a backup battery is not used,connect V CC to OUT and connect BATT to GND.
Replacing the Backup Battery
If BATT is decoupled with a 0.1μF capacitor to ground,the backup power source can be removed while V CC remains valid without danger of triggering a reset pulse.The device does not enter battery-backup mode when V CC stays above the reset threshold voltage.
Negative-Going V CC Transients
These supervisors are relatively immune to short-dura-tion, negative-going V CC transients. Resetting the μP
when V CC experiences only small glitches is usually not desirable.
The Typical Operating Characteristics section shows a graph of Maximum Transient Duration vs. Reset Threshold Overdrive for which reset is not asserted.The graph was produced using negative-going V CC pulses, starting at V CC and ending below the reset threshold by the magnitude indicated (reset threshold overdrive). The graph shows the maximum pulse width that a negative-going V CC transient can typically have without triggering a reset pulse. As the amplitude of the transient increases (i.e., goes further below the reset threshold), the maximum allowable pulse width decreases. Typically, a V CC transient that goes 100mV below the reset threshold and lasts for 30μs will not trigger a reset pulse.
A 0.1μF bypass capacitor mounted close to the V CC pin provides additional transient immunity.
Figure 1. MAX6362 Watchdog Timeout Period and Reset Active Time
M A X 6361–M A X 6364
Watchdog Software Considerations
(MAX6362 Only)
To help the watchdog timer monitor software execution more closely, set and reset the watchdog input at dif-ferent points in the program, rather than “pulsing” the watchdog input low-high-low. This technique avoids a “stuck” loop, in which the watchdog timer would contin-ue to be reset within the loop, keeping the watchdog from timing out. F igure 2 shows an example of a flow diagram where the I/O driving the WDI is set low at the beginning of the program, set high at the beginning of every subroutine or loop, then set low again when the program returns to the beginning. If the program should “hang” in any subroutine, the problem would quickly be corrected, since the I/O is continually set low and the watchdog timer is allowed to time out, trigger-ing a reset.
SOT23, Low-Power μP Supervisory Circuits with Battery Backup 8_______________________________________________________________________________________
Figure 2. Watchdog Flow Diagram
MAX6361–MAX6364
SOT23, Low-Power μP Supervisory Circuits
with Battery Backup
_______________________________________________________________________________________
9
*Sample stock generally held on standard versions only. Contact factory for availability of nonstandard versions.
Device Marking Codes
Selector Guide
M A X 6361–M A X 6364
SOT23, Low-Power μP Supervisory Circuits with Battery Backup 10______________________________________________________________________________________
Pin Configurations (continued)
Typical Operating Circuit
Chip Information
TRANSISTOR COUNT: 720
MAX6361–MAX6364
SOT23, Low-Power μP Supervisory Circuits
with Battery Backup
______________________________________________________________________________________11
Package Information
M A X 6361–M A X 6364
SOT23, Low-Power μP Supervisory Circuits with Battery Backup Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600?2005 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
NOTES