19-1658; Rev 1; 6/01
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
Features
♦ Low +1.2V Operating Supply Voltage (VCC or VBATT)
♦ Precision Monitoring of +5.0V, +3.3V, +3.0V, and
+2.5V Power-Supply Voltages
♦ On-Board Gating of Chip-Enable Signals, 1.5ns
Propagation Delay
♦ Debounced Manual Reset Input (MAX6365)
♦ Watchdog Timer, 1.6s Timeout (MAX6366)
♦ Battery-On Output Indicator (MAX6367)
♦ Auxiliary User-Adjustable RESET IN (MAX6368)
♦ Low 10µA Quiescent Supply Current
♦ Three Available Output Structures
Push-Pull RESET
Open-Drain RESET
Open-Drain RESET
♦ RESET/RESET Valid Down to 1.2V Guaranteed
(VCC or VBATT)
♦ Power-Supply Transient Immunity
♦ 150ms min Reset Timeout Period
♦ Miniature 8-Pin SOT23 Package
These devices perform four basic system functions:
1) Provide a µP 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 µPs, 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.
Applications
Ordering Information
PART*
TEMP. RANGE
PINPACKAGE
MA X6 36 5LKA_ _-T
-40°C to +85°C
8 SOT23-8
MAX6365PKA_ _-T
-40°C to +85°C
8 SOT23-8
MAX6365HKA_ _-T
-40°C to +85°C
8 SOT23-8
Critical µP/µC Power
Monitoring
Portable/BatteryPowered Equipment
MA X6 36 6LKA_ _-T
MAX6366PKA_ _-T
-40°C to +85°C
8 SOT23-8
-40°C to +85°C
8 SOT23-8
Fax Machines
Set-Top Boxes
MAX6366HKA_ _-T
-40°C to +85°C
8 SOT23-8
Industrial Control
POS Equipment
MA X6 36 7LKA_ _-T
-40°C to +85°C
8 SOT23-8
MAX6367PKA_ _-T
-40°C to +85°C
8 SOT23-8
MAX6367HKA_ _-T
-40°C to +85°C
8 SOT23-8
MA X6 36 8LKA_ _-T
-40°C to +85°C
8 SOT23-8
MAX6368PKA_ _-T
-40°C to +85°C
8 SOT23-8
MAX6368HKA_ _-T
-40°C to +85°C
8 SOT23-8
Computers/Controllers
Pin Configurations
TOP VIEW
RESET, RESET
1
CE IN
2
8
CE OUT
7
BATT
3
6
OUT
MR 4
5
VCC
MAX6365
GND
SOT23
Pin Configurations continued at end of data sheet.
*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.
Typical Operating Circuit appears at end of data sheet.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX6365–MAX6368
General Description
The MAX6365–MAX6368 supervisory circuits simplify
power-supply monitoring, battery-backup control functions, and memory write protection in microprocessor
(µP) systems. The circuits significantly improve the size,
accuracy, and reliability of modern systems with an ultrasmall integrated solution.
MAX6365–MAX6368
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
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 = +70°C)
8-Pin SOT23 (derate 8.75mW/°C above +70°C)........700mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature .....................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
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 = -40°C to +85°C. Typical values are at TA = +25°C,
unless otherwise noted.) (Note 1)
PARAMETER
Operating Voltage Range
(Note 2)
Supply Current
(Excluding IOUT)
SYMBOL
CONDITIONS
VCC, VBATT No load
ICC
No load, VCC > VTH
Supply Current in BatteryBackup Mode (Excluding IOUT)
IBACK
VBATT = 2.8V,
VCC = 0
BATT Standby Current
IBATT
5.5V > VCC > (VBATT
+ 0.2V)
VCC to OUT On-Resistance
RON
MIN
TYP
0
Reset Threshold
VCC Falling Reset Delay
2
VSW
VTH
tRD
V
10
30
12
35
VCC = 5.5V
15
50
TA = +25°C
1
TA = -40°C to +85°C
3
TA = +25°C
-0.1
0.02
TA = -40°C to +85°C
-1.0
0.02
VCC = 4.75V, IOUT = 150mA
3.1
VCC = 3.15V, IOUT = 65mA
3.7
VBATT = 3.0V, IOUT = 10mA
VBATT = 2.25V, IOUT = 5mA
Battery-Switchover Threshold
(VCC - VBATT)
5.5
VCC = 3.6V
VBATT = 4.5V, IOUT = 20mA
VOUT
UNITS
VCC = 2.8V
VCC = 2.38V, IOUT = 25mA
Output Voltage in BatteryBackup Mode
MAX
VCC < VTH
µA
µA
Ω
4.6
VBATT 0.2
VBATT 0.15
VBATT 0.15
V
Power-up
20
Power-down
-20
mV
MAX636_ _KA46
4.50
4.63
4.75
MAX636_ _KA44
4.25
4.38
4.50
MAX636_ _KA31
3.00
3.08
3.15
MAX636_ _KA29
2.85
2.93
3.00
MAX636_ _KA26
2.55
2.63
2.70
MAX636_ _KA23
2.25
2.32
2.38
VCC falling at 10V/ms
µA
20
_______________________________________________________________________________________
V
µs
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
(VCC = +2.4V to +5.5V, VBATT = +3.0V, CE IN = VCC, reset not asserted, TA = -40°C to +85°C. Typical values are at TA = +25°C,
unless otherwise noted.) (Note 1)
PARAMETER
Reset Active Timeout Period
SYMBOL
VOL
RESET Output Voltage
MIN
TYP
150
Reset asserted,
VBATT = 0
MAX
UNITS
280
ms
ISINK = 1.6mA,
VCC > 2.1V
0.3
ISINK = 100µA,
VCC > 1.2V
0.4
VOH
Reset not asserted
(MAX636_L only)
ISOURCE = 500µA,
VCC > VTH(MAX)
VOL
Reset not asserted
ISINK = 1.6mA,
VCC > VTH (MAX)
VOH
Reset not asserted,
VBATT = 0
(MAX636_H only)
(Note 3)
ILKG
MAX636_P and MAX636_H only
RESET Output Voltage
RESET Output Leakage Current
CONDITIONS
tRP
V
0.8 ✕
VCC
0.3
ISOURCE = 1mA,
VCC > 1.8V
0.7 ✕
VCC
ISOURCE = 200µA,
VCC > 1.2V
0.8 ✕
VCC
V
1
µA
MANUAL RESET (MAX6365 only)
0.3 ✕
VCC
VIL
MR Input Voltage
V
0.7 ✕
VCC
VIH
Pullup Resistance
20
Minimum Pulse Width
1
kΩ
µs
Glitch Immunity
VCC = 3.3V
100
ns
MR to Reset Delay
VCC = 3.3V
120
ns
WATCHDOG (MAX6366 only)
Watchdog Timeout Period
tWD
1.00
Minimum WDI Input Pulse Width
tWDI
100
1.65
2.25
s
ns
0.3 ✕
VCC
VIL
WDI Input Voltage
V
0.7 ✕
VCC
VIH
WDI Input Current
-1.0
1.0
µA
BATT ON (MAX6367 only)
Output Voltage
VOL
ISINK = 3.2mA, VBATT = 2.1V
0.4
Sink current, VCC = 5V
Output Short-Circuit Current
Source current, VBATT > 2V
60
10
30
V
mA
100
µA
_______________________________________________________________________________________
3
MAX6365–MAX6368
ELECTRICAL CHARACTERISTICS (continued)
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.4V to +5.5V, VBATT = +3.0V, CE IN = VCC, reset not asserted, TA = -40°C to +85°C. Typical values are at TA = +25°C,
unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
1.185
1.235
1.285
V
±0.01
±25
nA
RESET IN (MAX6368 only)
RESET IN Threshold
VRTH
RESET IN Leakage Current
RESET IN to Reset Delay
VOD = 50mV, RESET IN falling
1.5
µs
CHIP-ENABLE GATING
±1
CE IN Leakage Current
Reset asserted
CE IN to CE OUT Resistance
Reset not asserted (Note 4)
20
100
Ω
CE OUT Short-Circuit Current
Reset asserted, CE OUT = 0
0.75
2.0
mA
CE IN to CE OUT Propagation
Delay
50Ω source,
CLOAD = 50pF
VCC = 4.75V
1.5
7
VCC = 3.15V
2
9
µA
ns
0.8 ✕ VCC
VCC = 5V, VCC > VBATT, ISOURCE = 100µA
CE OUT Output Voltage High
V
VBATT 0.1
VCC = 0, VBATT > 2.2V, ISOURCE = 1µA
Reset-to-CE OUT Delay
Note 1:
Note 2:
Note 3:
Note 4:
12
µs
All devices are 100% production tested at TA = +25°C. 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 = +25°C, unless otherwise noted.)
BATTERY SUPPLY CURRENT
(BACKUP MODE) vs. TEMPERATURE
14
13
12
11
10
9
1.0
VBATT = 2.8V
0.8
0.6
VBATT = 2.0V
0.4
0.2
-40
-20
0
20
40
TEMPERATURE (°C)
60
80
8
7
5
0
20
40
TEMPERATURE (°C)
60
80
VBATT = 2.8V
4
3
VBATT = 5.0V
2
0
-20
VBATT = 2.0V
6
1
-40
MAX6365/8-03
VCC = 0
0
8
4
1.2
BATT-TO-OUT ON-RESISTANCE (Ω)
VCC = 5.0V
VBATT = 0
BATT-TO-OUT ON-RESISTANCE
vs. TEMPERATURE
MAX6365/8-02
15
BATTERY SUPPLY CURRENT (µA)
16
MAX6365/8-01
SUPPLY CURRENT
vs. TEMPERATURE (NO LOAD)
SUPPLY CURRENT (µA)
MAX6365–MAX6368
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
IOUT = 25mA
VCC = 0
-40
-20
0
20
40
TEMPERATURE (°C)
_______________________________________________________________________________________
60
80
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
RESET TIMEOUT PERIOD
vs. TEMPERATURE
0.8
0.6
VCC = 3.0V
IOUT = 65mA
0.4
VCC = 4.5V
IOUT = 150mA
0.2
200
195
0
20
40
60
-40
80
45
1V/ms
10V/ms
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
RESET THRESHOLD
vs. TEMPERATURE
MAXIMUM TRANSIENT DURATION
vs. RESET THRESHOLD OVERDRIVE
BATTERY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
4.5
4.0
3.5
3.0
MAX636_ 26 (VTH = 2.63V)
2.5
2.0
400
350
300
MAX636_ 46
(VTH = 4.63V)
250
200
RESET OCCURS
ABOVE CURVE
150
100
MAX636_ 26
(VTH = 2.63V)
50
20
40
TEMPERATURE (°C)
60
80
VTH = 2.93V
9
8
VBATT = 2.8V
7
6
VBATT = 2.5V
5
4
VBATT = 2.3V
3
2
1
0
0
0
10
BATTERY SUPPLY CURRENT (µA)
MAX6365/8-07
MAX636_ 46 (VTH = 4.63V)
-20
60
TEMPERATURE (°C)
5.0
-40
75
0
MAX6365/8-08
-20
90
15
MAXIMUM TRANSIENT DURATION (µs)
-40
0.25V/ms
105
30
190
0
THRESHOLD (V)
205
VCC FALLING
120
MAX6365/8-09
1.0
135
PROPAGATION DELAY (µs)
1.2
210
MAX6365/8-05
VCC = 2.3V
IOUT = 25mA
RESET TIMEOUT PERIOD (ms)
MAX6365/8-04
VCC TO OUT ON-RESISTANCE (Ω)
1.4
VCC TO RESET PROPAGATION DELAY
vs. TEMPERATURE
MAX6365/8-06
VCC TO OUT ON-RESISTANCE
vs. TEMPERATURE
1
10
100
1000
10,000
RESET THRESHOLD OVERDRIVE VTH - VCC (mV)
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
VCC (V)
_______________________________________________________________________________________
5
MAX6365–MAX6368
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX6368
RESET IN TO RESET PROPAGATION DELAY
vs. TEMPERATURE
PROPAGATION DELAY (µs)
1.235
VOD = 50mV
5
2.5
2.2
1.9
1.6
-20
0
20
40
60
-40
80
-20
0
20
40
60
VCC = 5V
0
80
50
VCC = 3.0V
15
10
VCC = 5.0V
5
VCE IN = VCC/2
VBATT = 0
MAX6365/8-14
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
VCC = 5.0V
VBATT = 0
1.1
1.0
0
0
2.0
WATCHDOG TIMEOUT PERIOD (s)
MAX6365/8-13
20
-20
100
MAX6366
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
25
CE IN TO CE OUT ON-RESISTANCE (Ω)
2
CLOAD (pF)
CE IN TO CE OUT ON-RESISTANCE
vs. TEMPERATURE
20
40
TEMPERATURE (°C)
6
VCC = 3V
3
TEMPERATURE (°C)
TEMPERATURE (°C)
-40
4
0
1.0
-40
CE IN = 0 TO VCC
DRIVER SOURCE
IMPEDANCE = 50Ω
1
1.3
1.234
MAX6365/8-12
2.8
PROPAGATION DELAY (ns)
MAX6365/8 -10
1.236
CHIP-ENABLE PROPAGATION DELAY
vs. CE OUT LOAD CAPACITANCE
MAX6365/8-11
MAX6368
RESET IN THRESHOLD
vs. TEMPERATURE
VRTH (V)
MAX6365–MAX6368
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
_______________________________________________________________________________________
150
200
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
PIN
NAME
FUNCTION
RESET
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.
RESET
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.
2
CE IN
Chip-Enable Input. The input to chip-enable gating circuitry. Connect to GND or OUT if not used.
3
GND
Ground
1
4
MR
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 20kΩ
pullup to VCC.
WDI
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).
BATT ON
MAX6367 Battery-On Output. BATT ON goes high when in battery backup mode.
RESET IN
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.
5
VCC
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.
6
OUT
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.
7
BATT
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.
8
CE OUT
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 12µs (typ) or until CE IN goes high,
whichever occurs first.
_______________________________________________________________________________________
7
MAX6365–MAX6368
Pin Description
MAX6365–MAX6368
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
Functional Diagram
BATT ON (MAX6367 ONLY)
1.235V
MAX6365
MAX6366
MAX6367
MAX6368
VCC
OUT
CHIP-ENABLE
OUTPUT
CONTROL
BATT
CE IN
CE OUT
20k
RESET
GENERATOR
MR
(MAX6365 ONLY)
WATCHDOG
TRANSITION
DETECTOR
WDI
(MAX6366 ONLY)
RESET IN
(MAX6368 ONLY)
RESET
(RESET)
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 µPs 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 12µs to allow completion of the read/write operation (Figure 1). After the 12µs delay expires, the CE
_______________________________________________________________________________________
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
Table 1. Input and Output Status in
Battery-Backup Mode
PIN
VCC
OUT
BATT
RESET/RESET
BATT ON
MR, RESET IN,
CE IN, WDI
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.
Inputs ignored
CE 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.
STATUS
Disconnected from OUT
Connected to BATT
Connected to OUT. Current drawn from
the battery is less than 1µA (at VBATT =
2.8V, excluding IOUT) when VCC = 0.
Asserted
High state
Connected to OUT
Manual Reset Input (MAX6365 Only)
Many µP-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 20kΩ 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 0.1µF 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 (12µs)
tRD
RESET
tRD
tRP
tRP
RESET
* 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
MAX6365–MAX6368
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 50Ω 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
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
WDI
tRP
tWD
tRP
tWD
RESET
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 µP activity through the watchdog input (WDI). If the µP becomes inactive, reset
asserts. To use the watchdog function, connect WDI to
a bus line or µP 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.
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 10µA 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
R1 = R2 [(VRTH / VREF) - 1]
Since the input current at RESET IN is 25nA (max),
large values (up to 1MΩ) 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 = 100kΩ, and calculate R1 = 273kΩ.
Reset Output
A µP’s reset input starts the µP in a known state. The
MAX6365–MAX6368 µP 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).
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
______________________________________________________________________________________
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
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.
Negative-Going VCC Transients
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 30µs will not trigger a reset pulse.
A 0.1µF bypass capacitor mounted close to the VCC
pin provides additional transient immunity.
These supervisors are relatively immune to short-duration, negative-going VCC transients. Resetting the µP
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,
+2.4V TO +5.5V
START
0.1µF
SET
WDI
LOW
BATT ON
VCC
OUT
BATT
CE OUT
CE
MAX6367
CMOS RAM
CE IN
ADDRESS
DECODE
A0–A15
µP
GND
RESET
SUBROUTINE
OR PROGRAM LOOP
SET WDI
HIGH
RESET
RETURN
Figure 3. MAX6367 BATT ON Driving an External Pass
Transistor
END
Figure 4. Watchdog Flow Diagram
______________________________________________________________________________________
11
MAX6365–MAX6368
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.
MAX6365–MAX6368
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
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
TOP MARK
PART
TOP MARK
PART
TOP MARK
AAAM
MAX6366PKA23
AABK
MAX6367HKA23
AACI
MAX6365LKA26
AAAL
MAX6366PKA26
AABJ
MAX6367HKA26
AACH
MAX6365LKA29*
AAAK
MAX6366PKA29*
AABI
MAX6367HKA29
AACG
MAX6365LKA31
AAAJ
MAX6366PKA31
AABH
MAX6367HKA31
AACF
MAX6365LKA44
AAAI
MAX6366PKA44
AABG
MAX6367HKA44
AACE
MAX6365LKA46*
AAAH
MAX6366PKA46*
AABF
MAX6367HKA46*
AACD
MAX6365PKA23
AAAS
MAX6366HKA23
AABQ
MAX6368LKA23
AACO
MAX6365PKA26
AAAR
MAX6366HKA26
AABP
MAX6368LKA26
AACN
MAX6365PKA29*
AAAQ
MAX6366HKA29
AABO
MAX6368LKA29*
AACM
MAX6365PKA31
AAAP
MAX6366HKA31
AABN
MAX6368LKA31
AACL
AACK
MAX6365PKA44
AAAO
MAX6366HKA44
AABM
MAX6368LKA44
MAX6365PKA46*
AAAN
MAX6366HKA46*
AABL
MAX6368LKA46*
AACJ
MAX6365HKA23
AAAY
MAX6367LKA23
AABW
MAX6368PKA23
AACU
MAX6365HKA26
AAAX
MAX6367LKA26
AABV
MAX6368PKA26
AACT
MAX6365HKA29
AAAW
MAX6367LKA29*
AABU
MAX6368PKA29*
AACS
MAX6365HKA31
AAAV
MAX6367LKA31
AABT
MAX6368PKA31
AACR
MAX6365HKA44
AAAU
MAX6367LKA44
AABS
MAX6368PKA44
AACQ
MAX6365HKA46*
AAAT
MAX6367LKA46*
AABR
MAX6368PKA46*
AACP
MAX6366LKA23
AABE
MAX6367PKA23
AACC
MAX6368HKA23
AADA
MAX6366LKA26
AABD
MAX6367PKA26
AACB
MAX6368HKA26
AACZ
MAX6366LKA29*
AABC
MAX6367PKA29*
AACA
MAX6368HKA29
AACY
MAX6366LKA31
AABB
MAX6367PKA31
AABZ
MAX6368HKA31
AACX
MAX6366LKA44
AABA
MAX6367PKA44
AABY
MAX6368HKA44
AACW
MAX6366LKA46*
AAAZ
MAX6367PKA46*
AABX
MAX6368HKA46*
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
______________________________________________________________________________________
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
MANUAL
RESET
INPUT
PART
MAX6365LKA__
MAX6365PKA__
MAX6365HKA__
WATCHDOG
INPUT
BATT
ON
RESET
PUSHPULL
RESET
IN
RESET
OPENDRAIN
RESET
OPENDRAIN
MAX6366LKA__
MAX6366PKA__
MAX6366HKA__
MAX6367PKA__
MAX6367HKA__
MAX6368PKA__
MAX6368HKA__
MAX6368LKA__
MAX6367LKA__
CHIPENABLE
GATING
Pin Configurations (continued)
TOP VIEW
RESET, RESET
1
CE IN
2
RESET, RESET 1
8
CE OUT
7
BATT
3
6
OUT
BATT ON 4
5
VCC
8
CE OUT
7
BATT
CE IN
3
6
OUT
GND
WDI 4
5
VCC
2
MAX6367
MAX6366
GND
SOT23
SOT23
RESET, RESET 1
8
CE OUT
7
BATT
3
6
OUT
RESET IN 4
5
VCC
CE IN
2
MAX6368
GND
SOT23
______________________________________________________________________________________
13
MAX6365–MAX6368
Selector Guide
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
MAX6365–MAX6368
Typical Operating Circuit
+2.4V TO +5.5V
CMOS
RAM
0.1µF
CE
VCC
BATT
OUT
MAX6366
MAX6368
SECONDARY
DC VOLTAGE
REALTIME
CLOCK
0.1µF
A0–A15
RESET
RESET
R1
µP
I/O
RESET IN* WDI**
R2
CE IN
CE OUT
GND
ADDRESS
DECODE
*RESET IN APPLIES TO MAX6368 ONLY.
**WDI APPLIES TO MAX6366 ONLY.
Chip Information
TRANSISTOR COUNT: 729
PROCESS: CMOS
14
______________________________________________________________________________________
SOT23, Low-Power µP Supervisory Circuits
with Battery Backup and Chip-Enable Gating
SOT23, 8L.EPS
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
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX6365–MAX6368
Package Information
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