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19-1658; Rev 1; 6/01
SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating
General Description
The MAX6365-MAX6368 supervisory circuits simplify power-supply monitoring, battery-backup control functions, and memory write protection in microprocessor (P) systems. The circuits significantly improve the size, accuracy, and reliability of modern systems with an ultrasmall integrated solution. These devices perform four basic system functions: 1) Provide a P reset output during VCC supply powerup, power-down, and brownout conditions. 2) Internally control VCC to backup-battery switching to maintain data or low-power operation for CMOS RAM, CMOS Ps, real-time clocks, and other digital logic when the main supply fails. 3) Provide memory write protection through internal chip-enable gating during supply or processor faults. 4) Include one of the following options: a manual reset input (MAX6365), a watchdog timer function (MAX6366), a battery-on output (MAX6367), or an auxiliary user-adjustable reset input (MAX6368). The MAX6365-MAX6368 operate from VCC supply voltages as low as 1.2V. The factory preset reset threshold voltages range from 2.32V to 4.63V (see Ordering Information). In addition, each part is offered in three reset output versions: push-pull active low, open-drain active low, or open-drain active high (see Selector Guide). The MAX6365-MAX6368 are available in miniature 8-pin SOT23 packages.
Features
o Low +1.2V Operating Supply Voltage (VCC or VBATT) o Precision Monitoring of +5.0V, +3.3V, +3.0V, and +2.5V Power-Supply Voltages o On-Board Gating of Chip-Enable Signals, 1.5ns Propagation Delay o Debounced Manual Reset Input (MAX6365) o Watchdog Timer, 1.6s Timeout (MAX6366) o Battery-On Output Indicator (MAX6367) o Auxiliary User-Adjustable RESET IN (MAX6368) o Low 10A Quiescent Supply Current o Three Available Output Structures Push-Pull RESET Open-Drain RESET Open-Drain RESET o RESET/RESET Valid Down to 1.2V Guaranteed (VCC or VBATT) o Power-Supply Transient Immunity o 150ms min Reset Timeout Period o Miniature 8-Pin SOT23 Package
MAX6365-MAX6368
Ordering Information
PART* MA X6 36 5LKA_ _-T MAX6365PKA_ _-T MAX6365HKA_ _-T MA X6 36 6LKA_ _-T MAX6366PKA_ _-T MAX6366HKA_ _-T MA X6 36 7LKA_ _-T MAX6367PKA_ _-T MAX6367HKA_ _-T MA X6 36 8LKA_ _-T MAX6368PKA_ _-T MAX6368HKA_ _-T TEMP. RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C PINPACKAGE 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8 8 SOT23-8
Applications
Critical P/C Power Monitoring Fax Machines Industrial Control Computers/Controllers Portable/BatteryPowered Equipment Set-Top Boxes POS Equipment
Pin Configurations
TOP VIEW
RESET, RESET CE IN GND 1 2 8 7 CE OUT BATT OUT VCC
MAX6365
3 6 5 MR 4
*These parts offer a choice of reset threshold voltages. From the Reset Threshold Ranges table, insert the desired threshold voltage code in the blank to complete the part number. SOT parts come in tape-and-reel only and must be ordered in 2500-piece increments. See Device Marking Codes for a complete parts list, including SOT top marks and standard threshold versions. See Selector Guide for a listing of device features.
SOT23 Pin Configurations continued at end of data sheet.
Typical Operating Circuit appears at end of data sheet. 1
________________________________________________________________ Maxim Integrated Products
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SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating MAX6365-MAX6368
ABSOLUTE MAXIMUM RATINGS
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, CE IN, CE OUT ...........................-0.3V to (VOUT + 0.3V) MR ..............................................................-0.3V to (VCC + 0.3V) Input Current VCC Peak ..............................................................................1A VCC Continuous .............................................................250mA BATT Peak .....................................................................250mA BATT Continuous .............................................................40mA GND ...............................................................................75mA Output Current OUT ...............................Short-Circuit Protected for up to 10s RESET, RESET, BATT ON, CE OUT...............................20mA Continuous Power Dissipation (TA = +70C) 8-Pin SOT23 (derate 8.75mW/C above +70C)........700mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Junction Temperature .....................................................+150C Lead Temperature (soldering, 10s) .................................+300C
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.
ELECTRICAL CHARACTERISTICS
(VCC = +2.4V to +5.5V, VBATT = +3.0V, CE IN = VCC, reset not asserted, TA = -40C to +85C. Typical values are at TA = +25C, unless otherwise noted.) (Note 1)
PARAMETER Operating Voltage Range (Note 2) Supply Current (Excluding IOUT) Supply Current in BatteryBackup Mode (Excluding IOUT) BATT Standby Current SYMBOL VCC, VBATT No load VCC = 2.8V ICC No load, VCC > VTH VBATT = 2.8V, VCC = 0 5.5V > VCC > (VBATT + 0.2V) VCC = 3.6V VCC = 5.5V IBACK IBATT TA = +25C TA = -40C to +85C TA = +25C TA = -40C to +85C -0.1 -1.0 CONDITIONS MIN 0 10 12 15 TYP MAX 5.5 30 35 50 1 3 0.02 0.02 3.1 3.7 4.6 VBATT 0.2 VBATT 0.15 VBATT 0.15 20 -20 4.50 4.25 3.00 2.85 2.55 2.25 4.63 4.38 3.08 2.93 2.63 2.32 20 4.75 4.50 3.15 3.00 2.70 2.38 s V A A A UNITS V
VCC = 4.75V, IOUT = 150mA VCC to OUT On-Resistance RON VCC = 3.15V, IOUT = 65mA VCC = 2.38V, IOUT = 25mA VBATT = 4.5V, IOUT = 20mA Output Voltage in BatteryBackup Mode VOUT VBATT = 3.0V, IOUT = 10mA VBATT = 2.25V, IOUT = 5mA Battery-Switchover Threshold (VCC - VBATT) VSW VCC < VTH MAX636_ _KA46 MAX636_ _KA44 Reset Threshold VTH MAX636_ _KA31 MAX636_ _KA29 MAX636_ _KA26 MAX636_ _KA23 VCC Falling Reset Delay tRD VCC falling at 10V/ms Power-up Power-down
V
mV
2
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SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.4V to +5.5V, VBATT = +3.0V, CE IN = VCC, reset not asserted, TA = -40C to +85C. Typical values are at TA = +25C, unless otherwise noted.) (Note 1)
PARAMETER Reset Active Timeout Period SYMBOL tRP Reset asserted, VBATT = 0 Reset not asserted (MAX636_L only) Reset not asserted Reset not asserted, VBATT = 0 (MAX636_H only) (Note 3) ISINK = 1.6mA, VCC > 2.1V ISINK = 100A, VCC > 1.2V ISOURCE = 500A, VCC > VTH(MAX) ISINK = 1.6mA, VCC > VTH (MAX) ISOURCE = 1mA, VCC > 1.8V ISOURCE = 200A, VCC > 1.2V 0.7 VCC 0.8 VCC 1 0.3 VCC 0.7 VCC 20 1 VCC = 3.3V VCC = 3.3V tWD tWDI VIL WDI Input Voltage VIH WDI Input Current BATT ON (MAX6367 only) Output Voltage Output Short-Circuit Current VOL ISINK = 3.2mA, VBATT = 2.1V Sink current, VCC = 5V Source current, VBATT > 2V 10 60 30 100 0.4 V mA A 0.7 VCC -1.0 1.0 A 1.00 100 0.3 VCC 100 120 1.65 2.25 k s ns ns s ns A 0.8 VCC 0.3 V CONDITIONS MIN 150 TYP MAX 280 0.3 0.4 V UNITS ms
MAX6365-MAX6368
VOL RESET Output Voltage VOH VOL RESET Output Voltage VOH
RESET Output Leakage Current MANUAL RESET (MAX6365 only)
ILKG
MAX636_P and MAX636_H only
VIL MR Input Voltage VIH Pullup Resistance Minimum Pulse Width Glitch Immunity MR to Reset Delay WATCHDOG (MAX6366 only) Watchdog Timeout Period Minimum WDI Input Pulse Width
V
V
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3
SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating MAX6365-MAX6368
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.4V to +5.5V, VBATT = +3.0V, CE IN = VCC, reset not asserted, TA = -40C to +85C. Typical values are at TA = +25C, unless otherwise noted.) (Note 1)
PARAMETER RESET IN (MAX6368 only) RESET IN Threshold RESET IN Leakage Current RESET IN to Reset Delay CHIP-ENABLE GATING CE IN Leakage Current CE IN to CE OUT Resistance CE OUT Short-Circuit Current CE IN to CE OUT Propagation Delay Reset asserted Reset not asserted (Note 4) Reset asserted, CE OUT = 0 50 source, CLOAD = 50pF VCC = 4.75V VCC = 3.15V 0.8 VCC V VCC = 0, VBATT > 2.2V, ISOURCE = 1A Reset-to-CE OUT Delay VBATT 0.1 12 s 20 0.75 1.5 2 1 100 2.0 7 9 A mA ns VOD = 50mV, RESET IN falling VRTH 1.185 1.235 0.01 1.5 1.285 25 V nA s SYMBOL CONDITIONS MIN TYP MAX UNITS
VCC = 5V, VCC > VBATT, ISOURCE = 100A CE OUT Output Voltage High
Note 1: Note 2: Note 3: Note 4:
All devices are 100% production tested at TA = +25C. Limits over temperature are guaranteed by design. VBATT can be 0 anytime, or VCC can go down to 0 if VBATT is active (except at startup). RESET is pulled up to OUT. Specifications apply for OUT = VCC or OUT = BATT. The chip-enable resistance is tested with VCC = VTH(MAX) and CE IN = VCC/2.
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE (NO LOAD)
MAX6365/8-01
BATTERY SUPPLY CURRENT (BACKUP MODE) vs. TEMPERATURE
MAX6365/8-02
BATT-TO-OUT ON-RESISTANCE vs. TEMPERATURE
7 6 5 4 3 2 1 0 IOUT = 25mA VCC = 0 -40 -20 0 20 40 60 80 VBATT = 2.8V VBATT = 5.0V VBATT = 2.0V
MAX6365/8-03
16 15 SUPPLY CURRENT (A) 14 13 12 11 10 9 8
1.2 BATTERY SUPPLY CURRENT (A) 1.0 0.8 0.6 VBATT = 2.0V 0.4 0.2 0
VBATT = 2.8V
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (C)
TEMPERATURE (C)
BATT-TO-OUT ON-RESISTANCE ()
VCC = 5.0V VBATT = 0
VCC = 0
8
TEMPERATURE (C)
4
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SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
VCC TO OUT ON-RESISTANCE vs. TEMPERATURE
MAX6365/8-04
MAX6365-MAX6368
RESET TIMEOUT PERIOD vs. TEMPERATURE
MAX6365/8-05
VCC TO RESET PROPAGATION DELAY vs. TEMPERATURE
135 120 PROPAGATION DELAY (s) 105 90 75 60 45 30 15 10V/ms -40 -20 0 20 40 60 80 1V/ms VCC FALLING 0.25V/ms
MAX6365/8-06
1.4 VCC TO OUT ON-RESISTANCE () 1.2 1.0 0.8 0.6 0.4 0.2 0 -40 -20 0 20 40 60 80 TEMPERATURE (C) VCC = 4.5V IOUT = 150mA VCC = 3.0V IOUT = 65mA VCC = 2.3V IOUT = 25mA
210
RESET TIMEOUT PERIOD (ms)
205
200
195
190 -40 -20 0 20 40 60 80 TEMPERATURE (C)
0 TEMPERATURE (C)
RESET THRESHOLD vs. TEMPERATURE
MAX6365/8-07
MAXIMUM TRANSIENT DURATION vs. RESET THRESHOLD OVERDRIVE
MAX6365/8-08
BATTERY SUPPLY CURRENT vs. SUPPLY VOLTAGE
9 BATTERY SUPPLY CURRENT (A) 8 7 6 5 4 3 2 1 0 VBATT = 2.3V VBATT = 2.5V VBATT = 2.8V VTH = 2.93V
MAX6365/8-09
5.0 MAX636_ 46 (VTH = 4.63V) 4.5 THRESHOLD (V) 4.0 3.5 3.0 MAX636_ 26 (VTH = 2.63V) 2.5 2.0 -40 -20 0 20 40 60 80 TEMPERATURE (C)
400 MAXIMUM TRANSIENT DURATION (s) 350 300 250 200 150 100 50 0 1 10 100 1000 MAX636_ 26 (VTH = 2.63V) RESET OCCURS ABOVE CURVE MAX636_ 46 (VTH = 4.63V)
10
10,000
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
RESET THRESHOLD OVERDRIVE VTH - VCC (mV)
VCC (V)
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5
SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating MAX6365-MAX6368
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
MAX6368 RESET IN THRESHOLD vs. TEMPERATURE
MAX6365/8 -10
MAX6368 RESET IN TO RESET PROPAGATION DELAY vs. TEMPERATURE
2.8 PROPAGATION DELAY (s) 2.5 2.2 1.9 1.6 1.3 VOD = 50mV
MAX6365/8-11
CHIP-ENABLE PROPAGATION DELAY vs. CE OUT LOAD CAPACITANCE
CE IN = 0 TO VCC DRIVER SOURCE IMPEDANCE = 50 VCC = 3V 3
MAX6365/8-12
1.236
5
1.235
PROPAGATION DELAY (ns)
4
VRTH (V)
2
VCC = 5V
1
1.234 -40 -20 0 20 40 60 80 TEMPERATURE (C)
1.0 -40 -20 0 20 40 60 80 TEMPERATURE (C)
0 0 50 100 CLOAD (pF) 150 200
CE IN TO CE OUT ON-RESISTANCE vs. TEMPERATURE
MAX6365/8-13
MAX6366 WATCHDOG TIMEOUT PERIOD vs. TEMPERATURE
1.9 WATCHDOG TIMEOUT PERIOD (s) 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 VCC = 5.0V VBATT = 0 -40 -20 0 20 40 60 80
MAX6365/8-14
25
CE IN TO CE OUT ON-RESISTANCE ()
2.0
20 VCC = 3.0V 15
10 VCC = 5.0V 5 VCE IN = VCC/2 VBATT = 0 0 -40 -20 0 20 40 60 80 TEMPERATURE (C)
TEMPERATURE (C)
6
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SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating
Pin Description
PIN NAME FUNCTION Active-High Reset Output. RESET asserts high continuously when VCC is below the reset threshold (VTH), MR is low, or RESET IN is low. It asserts in pulses when the internal watchdog times out. RESET remains asserted for the reset timeout period (tRP) after VCC rises above the reset threshold, after the manual reset input goes from low to high, after RESET IN goes high, or after the watchdog triggers a reset event. RESET is an open-drain active-high reset output. Active-Low Reset Output. RESET asserts low continuously when V C C is below the reset threshold (VTH), the manual reset input is low, or RESET IN is low. It asserts low in pulses when the internal watchdog times out. RESET remains asserted low for the reset timeout period (tRP) after V C C rises above the reset threshold, after the manual reset input goes from low to high, after RESET IN goes high, or after the watchdog triggers a reset event. The MAX636_L is an active-low pushpull output, while the MAX636_P is an active-low open-drain output. Chip-Enable Input. The input to chip-enable gating circuitry. Connect to GND or OUT if not used. Ground MAX6365 Manual-Reset Input. Maintaining logic low on MR asserts a reset. Reset output remains asserted as long as MR is low and for the reset timeout period (tRP) after MR transitions from low to high. Leave unconnected, or connect to VCC if not used. MR has an internal 20k pullup to VCC. MAX6366 Watchdog Input. If WDI remains high or low for longer than the watchdog timeout period (t WD ), the internal watchdog timer runs out and a reset pulse is triggered for the reset timeout period (tRP). The internal watchdog clears whenever reset asserts or whenever WDI sees a rising or falling edge (Figure 2). MAX6367 Battery-On Output. BATT ON goes high when in battery backup mode. MAX6368 Reset Input. When RESET IN falls below 1.235V, reset asserts. Reset output remains asserted as long as RESET IN is low and for at least tRP after RESET IN goes high. Supply Voltage, 1.2V to 5.5V. Reset asserts when V C C drops below the reset threshold voltage (VTH). Reset remains asserted until V C C rises above VTH and for at least tRP after V C C rises above VTH. Output. OUT sources from V C C when not in reset and from the greater of VCC or BATT when V C C is below the reset threshold. Backup-Battery Input. When V C C falls below the reset threshold, OUT switches to BATT if VBATT is 20mV greater than V C C . When V C C rises 20mV above VBATT, OUT switches to V C C . The 40mV hysteresis prevents repeated switching if VCC falls slowly. Chip-Enable Output. CE OUT goes low only when CE IN is low and reset is not asserted. If CE IN is low when reset is asserted, CE OUT will stay low for 12s (typ) or until CE IN goes high, whichever occurs first.
MAX6365-MAX6368
RESET
1
RESET
2 3
CE IN GND
MR
4
WDI
BATT ON RESET IN
5
VCC
6
OUT
7
BATT
8
CE OUT
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7
SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating MAX6365-MAX6368
Functional Diagram
BATT ON (MAX6367 ONLY)
1.235V
VCC
MAX6365 MAX6366 MAX6367 MAX6368
OUT CHIP-ENABLE OUTPUT CONTROL
BATT CE IN 20k MR (MAX6365 ONLY) RESET GENERATOR CE OUT
RESET (RESET)
WDI (MAX6366 ONLY) RESET IN (MAX6368 ONLY)
WATCHDOG TRANSITION DETECTOR
WATCHDOG TIMER
1.235V
GND
Detailed Description
The Typical Operating Circuit shows a typical connection for the MAX6365-MAX6368. OUT powers the static random-access memory (SRAM). If VCC is greater than the reset threshold (VTH), or if VCC is lower than VTH but higher than VBATT, VCC is connected to OUT. If VCC is lower than VTH and VCC is less than VBATT, BATT is connected to OUT. OUT supplies up to 150mA from VCC. In battery-backup mode, 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 BATT-to-OUT On-Resistance vs. Temperature graph in the Typical Operating Characteristics.
Chip-Enable Signal Gating
The MAX6365-MAX6368 provide internal gating of CE signals to prevent erroneous data from being written to
8
CMOS RAM in the event of a power failure. During normal operation, the CE gate is enabled and passes all CE transitions. When reset asserts, this path becomes disabled, preventing erroneous data from corrupting the CMOS RAM. All of these devices use a series transmission gate from CE IN to CE OUT. The 2ns propagation delay from CE IN to CE OUT allows the devices to be used with most Ps and high-speed DSPs. During normal operation, CE IN is connected to CE OUT through a low on-resistance transmission gate. This is valid when reset is not asserted. If CE IN is high when reset is asserted, CE OUT remains high regardless of any subsequent transitions on CE IN during the reset event. If CE IN is low when reset is asserted, CE OUT is held low for 12s to allow completion of the read/write operation (Figure 1). After the 12s delay expires, the CE
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SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating
OUT goes high and stays high regardless of any subsequent transitions on CE IN during the reset event. When CE OUT is disconnected from CE IN, CE OUT is actively pulled up to OUT. The propagation delay through the chip-enable circuitry depends on both the source impedance of the drive to CE IN and the capacitive loading at CE OUT. The chip-enable propagation delay is production tested from the 50% point of CE IN to the 50% point of CE OUT, using a 50 driver and 50pF load capacitance. Minimize the capacitive load at CE OUT to minimize propagation delay, and use a low-output-impedance driver.
MAX6365-MAX6368
Table 1. Input and Output Status in Battery-Backup Mode
PIN VCC OUT BATT RESET/RESET BATT ON MR, RESET IN, CE IN, WDI CE OUT STATUS Disconnected from OUT Connected to BATT Connected to OUT. Current drawn from the battery is less than 1A (at VBATT = 2.8V, excluding IOUT) when VCC = 0. Asserted High state Inputs ignored Connected to OUT
Backup-Battery Switchover
In a brownout or power failure, it may be necessary to preserve the contents of the RAM. With a backup battery installed at BATT, the MAX6365-MAX6368 automatically switch the RAM to backup power when VCC falls. The MAX6367 has a BATT ON output that goes high in battery-backup mode. These devices require two conditions before switching to battery-backup mode: 1) VCC must be below the reset threshold. 2) VCC must be below VBATT. Table 1 lists the status of the inputs and outputs in battery-backup mode. The devices do not power up if the only voltage source is on BATT. OUT only powers up from VCC at startup.
Manual Reset Input (MAX6365 Only)
Many P-based products require manual reset capability, allowing the user or external logic circuitry to initiate a reset. For the MAX6365, a logic low on MR asserts reset. Reset remains asserted while MR is low and for a minimum of 150ms (tRP) after it returns high. MR has an internal 20k pullup resistor to VCC. This input can be driven with TTL/CMOS logic levels or with open-drain/collector outputs. Connect a normally 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 0.1F capacitor from MR to GND to provide additional noise immunity.
VCC OR BATT RESET THRESHOLD VTH CE IN
CE OUT RESET-TO-CE OUT DELAY (12s) tRD RESET RESET tRP tRD tRP *
* IF CE IN GOES HIGH BEFORE RESET ASSERTS, CE OUT GOES HIGH WITHOUT DELAY AS CE IN GOES HIGH.
Figure 1. Reset and Chip-Enable Timing _______________________________________________________________________________________ 9
SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating MAX6365-MAX6368
WDI
tRP tWD RESET tWD
tRP
tWD = WATCHDOG TIMEOUT PERIOD tRP = RESET TIMEOUT PERIOD
Figure 2. MAX6366 Watchdog Timeout Period and Reset Active Time
Watchdog Input (MAX6366 Only)
The watchdog monitors P activity through the watchdog input (WDI). If the P becomes inactive, reset asserts. To use the watchdog function, connect WDI to a bus line or P I/O line. A change of state (high to low, low to high, or a minimum 100ns pulse) resets the watchdog timer. If WDI remains high or low for longer than the watchdog timeout period (tWD), 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 whenever WDI sees a rising or falling edge. If WDI remains in either a high or low state, a reset pulse asserts periodically after every tWD (Figure 2). Leave WDI unconnected to disable the watchdog function.
R1 = R2 [(VRTH / VREF) - 1] Since the input current at RESET IN is 25nA (max), large values (up to 1M) can be used for R2 with no significant loss in accuracy. For example, in the Typical Operating Circuit, the MAX6368 monitors two supply voltages. To monitor the secondary 5V logic or analog supply with a 4.60V nominal programmed reset threshold, choose R2 = 100k, and calculate R1 = 273k.
Reset Output
A P's reset input starts the P in a known state. The MAX6365-MAX6368 P supervisory circuits assert a reset to prevent code-execution errors during powerup, power-down, and brownout conditions. RESET is guaranteed to be a logic low or logic high, depending on the device chosen (see Ordering Information). RESET or RESET asserts when VCC is below the reset threshold and for at least 150ms (tRP) after VCC rises above the reset threshold. RESET or RESET also asserts when MR is low (MAX6365) and when RESET IN is less than 1.235V (MAX6368). The MAX6366 watchdog function will cause RESET (or RESET) to assert in pulses following a watchdog timeout (Figure 2).
BATT ON Indicator (MAX6367 Only)
BATT ON is a push-pull output that drives high when in battery-backup mode. BATT ON typically sinks 3.2mA at 0.1V saturation voltage. In battery-backup mode, this terminal sources approximately 10A from OUT. Use BATT ON to indicate battery-switchover status or to supply base drive to an external pass transistor for higher current applications (Figure 3).
RESET IN Comparator (MAX6368 Only)
RESET IN is compared to an internal 1.235V reference. If the voltage at RESET IN is less than 1.235V, reset asserts. Use the RESET IN comparator as an undervoltage detector to signal a failing power supply or as a secondary power-supply reset monitor. To program the reset threshold (VRTH) of the secondary power supply, use the following (see Typical Operating Circuit): VRTH = VREF (R1 / R2 + 1) where VREF = 1.235V. To simplify the resistor selection, choose a value for R2 and calculate R1:
10
Applications Information
Operation Without a Backup Power Source
The MAX6365-MAX6368 provide battery-backup functions. If a backup power source is not used, connect BATT to GND and OUT to VCC.
Watchdog Software Considerations
One way to help the watchdog timer monitor the software execution more closely is to set and reset the watchdog at different points in the program rather than pulsing the watchdog input periodically. Figure 4 shows a flow diagram in which the I/O driving the
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SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating
watchdog is set low in the beginning of the program, set high at the beginning of every subroutine or loop, and set low again when the program returns to the beginning. If the program should hang in any subroutine, the problem would be quickly corrected. starting at VCC and ending below the reset threshold by the magnitude indicated (reset threshold overdrive). The graph shows the maximum pulse width that a negative-going VCC 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 VCC transient that goes 100mV below the reset threshold and lasts for 30s will not trigger a reset pulse. A 0.1F bypass capacitor mounted close to the VCC pin provides additional transient immunity.
MAX6365-MAX6368
Replacing the Backup Battery
When VCC is above VTH, the backup power source can be removed without danger of triggering a reset pulse. The device does not enter battery-backup mode when VCC stays above the reset threshold voltage. These supervisors are relatively immune to short-duration, negative-going VCC transients. Resetting the P when VCC experiences only small glitches is usually not desirable. The Typical Operating Characteristics section has a Maximum Transient Duration vs. Reset Threshold Overdrive graph for which reset is not asserted. The graph was produced using negative-going VCC pulses,
Negative-Going VCC Transients
+2.4V TO +5.5V START 0.1F
VCC
BATT ON OUT
SET WDI LOW CE
BATT
CE OUT
MAX6367
CMOS RAM CE IN ADDRESS DECODE A0-A15 P GND RESET RESET SUBROUTINE OR PROGRAM LOOP SET WDI HIGH
RETURN
Figure 3. MAX6367 BATT ON Driving an External Pass Transistor
END
Figure 4. Watchdog Flow Diagram
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11
SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating MAX6365-MAX6368
Reset Threshold Ranges
SUFFIX 46 44 31 29 26 23 RESET THRESHOLD RANGES (V) MIN TYP MAX 4.50 4.63 4.75 4.25 4.38 4.50 3.00 3.08 3.15 2.85 2.93 3.00 2.55 2.63 2.70 2.25 2.32 2.38
Device Marking Codes
PART MAX6365LKA23 MAX6365LKA26 MAX6365LKA29* MAX6365LKA31 MAX6365LKA44 MAX6365LKA46* MAX6365PKA23 MAX6365PKA26 MAX6365PKA29* MAX6365PKA31 MAX6365PKA44 MAX6365PKA46* MAX6365HKA23 MAX6365HKA26 MAX6365HKA29 MAX6365HKA31 MAX6365HKA44 MAX6365HKA46* MAX6366LKA23 MAX6366LKA26 MAX6366LKA29* MAX6366LKA31 MAX6366LKA44 MAX6366LKA46* TOP MARK AAAM AAAL AAAK AAAJ AAAI AAAH AAAS AAAR AAAQ AAAP AAAO AAAN AAAY AAAX AAAW AAAV AAAU AAAT AABE AABD AABC AABB AABA AAAZ PART MAX6366PKA23 MAX6366PKA26 MAX6366PKA29* MAX6366PKA31 MAX6366PKA44 MAX6366PKA46* MAX6366HKA23 MAX6366HKA26 MAX6366HKA29 MAX6366HKA31 MAX6366HKA44 MAX6366HKA46* MAX6367LKA23 MAX6367LKA26 MAX6367LKA29* MAX6367LKA31 MAX6367LKA44 MAX6367LKA46* MAX6367PKA23 MAX6367PKA26 MAX6367PKA29* MAX6367PKA31 MAX6367PKA44 MAX6367PKA46* TOP MARK AABK AABJ AABI AABH AABG AABF AABQ AABP AABO AABN AABM AABL AABW AABV AABU AABT AABS AABR AACC AACB AACA AABZ AABY AABX PART MAX6367HKA23 MAX6367HKA26 MAX6367HKA29 MAX6367HKA31 MAX6367HKA44 MAX6367HKA46* MAX6368LKA23 MAX6368LKA26 MAX6368LKA29* MAX6368LKA31 MAX6368LKA44 MAX6368LKA46* MAX6368PKA23 MAX6368PKA26 MAX6368PKA29* MAX6368PKA31 MAX6368PKA44 MAX6368PKA46* MAX6368HKA23 MAX6368HKA26 MAX6368HKA29 MAX6368HKA31 MAX6368HKA44 MAX6368HKA46* TOP MARK AACI AACH AACG AACF AACE AACD AACO AACN AACM AACL AACK AACJ AACU AACT AACS AACR AACQ AACP AADA AACZ AACY AACX AACW AACV
*These standard versions are available in small quantities through Maxim Distribution. Sample stock is generally held on standard versions only. Contact factory for availability of nonstandard versions.
12
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SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating
Selector Guide
PART MAX6365LKA__ MAX6365PKA__ MAX6365HKA__ MAX6366LKA__ MAX6366PKA__ MAX6366HKA__ MAX6367LKA__ MAX6367PKA__ MAX6367HKA__ MAX6368LKA__ MAX6368PKA__ MAX6368HKA__ MANUAL RESET INPUT WATCHDOG INPUT BATT ON RESET IN RESET PUSHPULL RESET OPENDRAIN RESET OPENDRAIN CHIPENABLE GATING
MAX6365-MAX6368
Pin Configurations (continued)
TOP VIEW
RESET, RESET CE IN GND
1 2
8 7
CE OUT BATT OUT VCC
RESET, RESET 1 CE IN GND 2
8 7
CE OUT BATT OUT VCC
MAX6366
3 6 5 3 WDI 4 BATT ON 4
MAX6367
6 5
SOT23
SOT23
RESET, RESET 1 CE IN GND 2
8 7
CE OUT BATT OUT VCC
MAX6368
3 6 5 RESET IN 4
SOT23
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13
SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating MAX6365-MAX6368
Typical Operating Circuit
+2.4V TO +5.5V 0.1F CMOS RAM CE VCC BATT REALTIME CLOCK
OUT 0.1F A0-A15 RESET P I/O ADDRESS DECODE
SECONDARY DC VOLTAGE R1
MAX6366 MAX6368
RESET RESET IN* WDI** R2 CE IN CE OUT GND
*RESET IN APPLIES TO MAX6368 ONLY. **WDI APPLIES TO MAX6366 ONLY.
Chip Information
TRANSISTOR COUNT: 729 PROCESS: CMOS
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SOT23, Low-Power P Supervisory Circuits with Battery Backup and Chip-Enable Gating
Package Information
SOT23, 8L.EPS
MAX6365-MAX6368
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 15 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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