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19-3139; Rev 3; 1/05
Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer
General Description
The MAX6854/MAX6855/MAX6856/MAX6858/MAX6860- MAX6869 ultra-low-current (170nA, typ) microprocessor (P) supervisory circuits combine voltage monitoring, watchdog timer, and manual reset input functions in a 5pin SOT23 package. These devices assert a reset signal whenever the monitored voltage drops below the factorytrimmed reset threshold voltage, manual reset is asserted, or the watchdog timer expires. The reset output remains asserted for a minimum timeout period after VCC rises above the reset threshold and manual reset is deasserted. Factory-trimmed reset threshold voltages are offered from +1.575V to +4.625V in approximately 100mV increments (see Threshold Suffix Guide). Each device is offered with six minimum reset timeout options, ranging from 10ms to 1200ms. The MAX6854/MAX6855/MAX6856/MAX6858/MAX6860- MAX6869 are offered in a variety of configurations (see the Selector Guide). The MAX6854/MAX6855/MAX6856/ MAX6861-MAX6869 provide a manual reset input, MR. The MAX6864-MAX6869 offer a watchdog timer that monitors activity at the WDI input to prevent code execution errors. The MAX6864-MAX6869 offer watchdog timeout options of 3.3s or 209s (typ). The MAX6861/ MAX6862/MAX6863 feature a pin-selectable reset delay period of 10ms or 150ms (min). Push-pull active-low, push-pull active-high, and open-drain active-low reset outputs are available.
Features
o Ultra-Low 170nA (typ) Supply Current o Reset Thresholds from +1.575V to +4.625V in Approximately 100mV Increments o Six Minimum Reset Timeout Period Options from 10ms to 1200ms o Manual Reset Option o Watchdog Timer Option o Pin-Selectable 10ms/150ms (min) Reset Timeout Period (MAX6861/MAX6862/MAX6863) o Immune to Short VCC Transients o Guaranteed Reset Valid to VCC = +1.1V o Three Reset Output Options: Push-Pull RESET Push-Pull RESET Open-Drain RESET o No External Components o Small 5-Pin SOT23 Package o Pin Compatible to the TPS3836/TPS3837/TPS3838 (MAX6861/MAX6862/MAX6863)
MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
Ordering Information
PART MAX6854UK_ _D_-T TEMP RANGE -40C to +85C PIN-PACKAGE 5 SOT23-5
Applications
Portable/Battery-Powered Equipment PDAs/Cell Phones MP3 Players/Pagers Glucose Monitors/Patient Monitors
MAX6855UK_ _D_-T -40C to +85C 5 SOT23-5 Insert reset threshold suffix (see Table 2, Threshold Suffix Guide) after UK. Insert the number corresponding to the desired reset timeout period (see Table 4, Reset Timeout Period) after D.
Typical Operating Circuit
VCC 0.1F VCC RESET RESET VCC
Note: Sample stock is generally held on standard versions only (see Table 5, Standard Versions Table). Standard versions have an order increment of 2500 pieces. Nonstandard versions have an order increment of 10,000 pieces. Contact factory for availability of nonstandard versions.
Pin Configurations appear at end of data sheet. Selector Guide appears at end of data sheet. Ordering Information continued at end of data sheet.
MAX6864 MAX6867
MANUAL RESET MR GND WDI I/O
P
GND
________________________________________________________________ Maxim Integrated Products
1
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
ABSOLUTE MAXIMUM RATINGS
VCC, Open-Drain RESET to GND ..........................-0.3V to +6.0V MR, Push-Pull RESET, RESET, WDI, CT, I.C............................................-0.3V to (VCC + 0.3V) Input Current, Output Current (all pins)............................20mA Continuous Power Dissipation (TA = +70C) 5-Pin SOT23 (derate 7.1mW/C above +70C)............571mW Operating Temperature Range ...........................-40C to +85C Junction Temperature .....................................................+150C Storage Temperature Range .............................-65C to +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 = 1.2V to 5.5V, TA = -40C to +85C, unless otherwise specified. Typical values are at VCC = 2.5V, TA = +25C.) (Note 1)
PARAMETER Supply Voltage SYMBOL VCC TA 0C TA = -40C to +85C VCC > VTH, no load, reset output deasserted (Note 2) VCC = 5.0V VCC = 3.3V VCC = 1.8V VTH 2.5% 10 40 150 1200 300 600 CONDITIONS MIN 1.1 1.2 210 190 170 7 VTH 0.5 15 60 225 1800 450 900 40 0.3 0.3 0.3 0.8 x VCC 0.8 x VCC 25 nA V 25 80 300 2400 600 1200 s ms TYP MAX 5.5 5.5 400 380 370 15 VTH + 2.5% A V %VTH nA UNITS V
Supply Current
ICC
VCC < VTH, no load, reset output asserted VCC Reset Threshold Reset Threshold Hysteresis VTH VHYST VCC falling (see Table 2) Reset asserted to reset deasserted D1 D2 Reset Timeout Period tRP VCC = VTH + 150mV (Figures 2 and 3) D3 D4 D5 D6 VCC to Reset Delay tRD VCC falling from (VTH + 100mV) to (VTH - 100mV) at 10mV/s VCC 1.1V, ISINK = 50A, RESET asserted, TA 0C VOL RESET Output Voltage VCC 1.2V, ISINK = 100A, RESET asserted VCC 2.12V, ISINK = 1.2mA, RESET asserted VCC 1.71V, ISOURCE = 200A, RESET deasserted, push-pull RESET only VOH VCC 2.38V, ISOURCE = 500A, RESET deasserted, push-pull RESET only RESET deasserted
Open-Drain RESET Leakage Current
ILKG
2
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 1.2V to 5.5V, TA = -40C to +85C, unless otherwise specified. Typical values are at VCC = 2.5V, TA = +25C.) (Note 1)
PARAMETER SYMBOL CONDITIONS VCC 1.1V, ISOURCE = 10A, RESET asserted, TA 0C VCC 1.2V, ISOURCE = 10A, RESET asserted VOH RESET Output Voltage VCC 1.53V, ISOURCE = 200A, RESET asserted VCC 2.12V, ISOURCE = 500A, RESET asserted VCC 1.71V, ISINK = 500A, RESET deasserted VOL VCC 2.38V, ISINK = 1.2mA, RESET deasserted CT = GND or VCC VIH VIL VIH VIL tMPW tMRD 5 VIH VIL WDI = GND or VCC tWDI tWD (Note 3) S L 150 1.5 95 3.3 209 7.75 487 0.7 x VCC 0.3 x VCC 20 1 200 250 10 20 0.7 x VCC 0.3 x VCC 0.8 x VCC 0.2 x VCC MIN 0.8 x VCC 0.8 x VCC 0.8 x VCC V 0.8 x VCC 0.3 0.3 20 nA V TYP MAX UNITS
MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
CT Input Current CT Input Voltage MANUAL RESET INPUT MR Input Voltage MR Minimum Pulse Width MR Glitch Rejection MR to Reset Delay MR Pullup Resistance WATCHDOG TIMER (MAX6864-MAX6869) WDI Input Voltage WDI Input Current WDI Pulse Width Watchdog Timeout Period
V s ns ns k
V nA ns s
Note 1: Devices are tested at TA = +25C. Specifications for TA = -40C to +85C are guaranteed by design. Note 2: For the MAX6864-MAX6869, the watchdog period is 1s with tRISE and tFALL < 50ns. Note 3: Guaranteed by design.
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
Typical Operating Characteristics
(VCC = +2.5V, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX6854 toc01
SUPPLY CURRENT vs. TEMPERATURE
MAX6854 toc02
NORMALIZED RESET TIMEOUT PERIOD vs. TEMPERATURE
MAX6854 toc03
10.0 VTH = 2.23V
0.22 0.20 0.18 ICC (A) 0.16 0.14 VCC = 1.8V 0.12 RESET IS NOT ASSERTED VTH = 1.575V VCC = 3.3V VCC = 5.5V VCC = 2.5V
1.02
1.01 NORMALIZED tRP 85
TA = +85C ICC (A) 1.0 TA = +25C TA = -40C
1.00
0.99
0.1 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VCC (V)
0.10 -40 -15 10 35 60 TEMPERATURE (C)
0.98 -40 -15 10 35 60 85 TEMPERATURE (C)
NORMALIZED WATCHDOG TIMEOUT PERIOD vs. TEMPERATURE
MAX6854 toc04
MAXIMUM VCC TRANSIENT DURATION vs. RESET THRESHOLD OVERDRIVE
RESET OCCURS ABOVE THIS LINE
MAX684 toc05
1.8 1.6 NORMALIZED tWD 1.4 1.2 1.0 0.8 0.6
1000
TRANSIENT DURATION (s)
100
10
1 VCC FALLING FROM VTH +100mV
0.4 -40 -15 10 35 60 85 TEMPERATURE (C)
0.1 10 100 RESET THRESHOLD OVERDRIVE (mV) 1000
NORMALIZED RESET THRESHOLD VOLTAGE vs. TEMPERATURE
MAX6854 toc06
VCC TO RESET DELAY vs. TEMPERATURE
VCC = VTH + 100mV TO VTH - 100mV 60
MAX6854 toc07
1.010
70
1.005 NORMALIZED VTH tRD (s) -40 -15 10 35 60 85
50
1.000
40 0.995 30 0.990 TEMPERATURE (C)
20 -40 -15 10 35 60 85 TEMPERATURE (C)
4
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
Typical Operating Characteristics (continued)
(VCC = +2.5V, TA = +25C, unless otherwise noted.)
OUTPUT LOW VOLTAGE vs. SINK CURRENT
MAX6854 toc08
OUTPUT HIGH VOLTAGE vs. SOURCE CURRENT
MAX6854 toc09
SUPPLY CURRENT vs. WATCHDOG SWITCHING FREQUENCY
VCC = 2.5V
MAX6854 toc10
0.30 0.25 0.20 VOL (V) VCC = 1.8V 0.15 0.10 VCC = 3.3V 0.05 0 0 1000 2000 3000 4000
0.50 OUTPUT HIGH VOLTAGE (VCC - VOH) (V) 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0 VCC = 1.8V VCC = 2.5V
100
SUPPLY CURRENT (A) 1000
VCC = 2.5V
10
VCC = 3.3V
1
0.1 0 200 400 600 800 10 100 1k 10k 100k 1M 10M ISOURCE (A) WATCHDOG SWITCHING FREQUENCY (Hz)
5000
ISINK (A)
VCC TO RESET DELAY
MAX6854 toc11
MANUAL RESET DELAY
MAX6854 toc12
1.7V VTH = 1.575V 1.5V tRD
VCC 200mV/div
tMRD
MR 1V/div
RESET 1V/div 0
RESET 1V/div
10s/div
200ns/div
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
MAX6854/MAX6855/MAX6856 Pin Description
PIN MAX6854/ MAX6856 MAX6855 NAME FUNCTION
1
--
RESET
Active-Low Open-Drain or Push-Pull Reset Output. RESET transitions from high to low when VCC drops below the selected reset threshold or MR is pulled low. RESET remains low for the reset timeout period after VCC exceeds the device reset threshold and MR deasserts. Push-pull RESET outputs are referenced to VCC. Open-drain RESET outputs require an external pullup resistor. Ground. Connect all GND inputs to the same potential. Active-Low Manual Reset Input. Drive MR low to initiate a reset. The reset output remains asserted while MR is held low and for the reset timeout period after MR transitions high. Leave MR unconnected or connect to VCC if unused. MR is internally pulled up to VCC through 10k. Supply Voltage. Input for VCC reset monitor. For noisy systems, bypass VCC with a 0.1F capacitor to GND. Active-High Push-Pull Reset Output. RESET transitions from low to high when VCC drops below the selected reset threshold or MR is pulled low. RESET remains high for the reset timeout period after VCC exceeds the device reset threshold and MR deasserts. RESET is referenced to VCC.
2, 4
2, 4
GND
3
3
MR
5
5
VCC
--
1
RESET
MAX6858/MAX6860 Pin Description
PIN MAX6858/ MAX6860 1, 2 3 NAME I.C. GND RESET FUNCTION Internally Connected. For increased noise immunity, connect I.C. to GND. Ground Active-Low Open-Drain or Push-Pull Reset Output. RESET transitions from high to low when VCC drops below the selected reset threshold. RESET remains low for the reset timeout period after VCC exceeds the device reset threshold. Push-pull RESET outputs are referenced to VCC. Opendrain RESET outputs require an external pullup resistor. Supply Voltage. Input for VCC reset monitor. For noisy systems, bypass VCC with a 0.1F capacitor to GND.
4
5
VCC
6
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer
MAX6861/MAX6862/MAX6863 Pin Description
PIN MAX6861/ MAX6863 MAX6862 NAME FUNCTION
MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
1 2
1 2
CT GND
Reset Timeout Select Input. Connect CT low to select the D1 reset timeout output period (see Tables 1 and 4). Connect CT high (normally VCC) to select the D3 reset timeout period. Ground Active-Low Manual Reset Input. Drive MR low to initiate a reset. The reset output remains asserted while MR is held low and for the reset timeout period after MR transitions high. Leave MR unconnected or connect to VCC if unused. MR is internally pulled up to VCC through 10k. Active-Low Open-Drain or Push-Pull Reset Output. RESET transitions from high to low when VCC drops below the selected reset threshold or MR is pulled low. RESET remains low for the reset timeout period after VCC exceeds the device reset threshold and MR deasserts. Push-pull RESET outputs are referenced to VCC. Open-drain RESET outputs require an external pullup resistor. Supply Voltage. Input for VCC reset monitor. For noisy systems, bypass VCC with a 0.1F capacitor to GND. Active-High Push-Pull Reset Output. RESET transitions from low to high when VCC drops below the selected reset threshold or MR is pulled low. RESET remains high for the reset timeout period after VCC exceeds the device reset threshold and MR deasserts. RESET is referenced to VCC.
3
3
MR
4
--
RESET
5
5
VCC
--
4
RESET
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
MAX6864/MAX6865/MAX6866 Pin Description
PIN MAX6864/ MAX6866 MAX6865 NAME FUNCTION Active-Low Open-Drain or Push-Pull Reset Output. RESET transitions from high to low when VCC drops below the selected reset threshold, MR is pulled low, or the watchdog timer expires. RESET remains low for the reset timeout period after VCC exceeds the device reset threshold, MR deasserts, or after the watchog timer expires. Push-pull RESET outputs are referenced to VCC. Open-drain RESET outputs require an external pullup resistor. Ground Active-Low Manual Reset Input. Drive MR low to initiate a reset. The reset output remains asserted while MR is held low and for the reset timeout period after MR transitions high. Leave MR unconnected or connect to VCC if unused. MR is internally pulled up to VCC through 10k. Watchdog Input. If WDI remains high or low for longer than the watchdog timeout period, the internal watchdog timer expires, and a reset is triggered for the reset timeout period. The internal watchdog timer clears whenever reset is asserted, the manual reset is asserted, or WDI sees a rising or falling edge. Supply Voltage. Input for VCC reset monitor. For noisy systems, bypass VCC with a 0.1F capacitor to GND. Active-High Push-Pull Reset Output. RESET transitions from low to high when VCC drops below the selected reset threshold, MR is pulled low, or the watchdog timer expires. RESET remains high for the reset timeout period after VCC exceeds the device reset threshold, MR deasserts, or after the watchdog timer expires. RESET is referenced to VCC.
1
--
RESET
2
2
GND
3
3
MR
4
4
WDI
5
5
VCC
--
1
RESET
8
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer
MAX6867/MAX6868/MAX6869 Pin Description
PIN MAX6867/ MAX6869 NAME MAX6868 Watchdog Input. If WDI remains high or low for longer than the watchdog timeout period, the internal watchdog timer expires, and a reset is triggered for the reset timeout period. The internal watchdog timer clears whenever reset is asserted, the manual reset is asserted, or WDI sees a rising or falling edge. Ground Active-Low Manual Reset Input. Drive MR low to initiate a reset. The reset output remains asserted while MR is held low and for the reset timeout period after MR transitions high. Leave MR unconnected or connect to VCC if unused. MR is internally pulled up to VCC through 10k. Active-Low Open-Drain or Push-Pull Reset Output. RESET transitions from high to low when VCC drops below the selected reset threshold, MR is pulled low, or the watchdog timer expires. RESET remains low for the reset timeout period after VCC exceeds the device reset threshold, MR deasserts, or after the watchdog timer expires. Push-pull RESET outputs are referenced to VCC. Open-drain RESET outputs require an external pullup resistor. Supply Voltage. Input for VCC reset monitor. For noisy systems, bypass VCC with a 0.1F capacitor to GND. Active-High Push-Pull Reset Output. RESET transitions from low to high when VCC drops below the selected reset threshold, MR is pulled low, or the watchdog timer expires. RESET remains high for the reset timeout period after VCC exceeds the device reset threshold, MR deasserts, or after the watchdog timer expires. RESET is referenced to VCC. FUNCTION
MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
1
1
WDI
2
2
GND
3
3
MR
4
--
RESET
5
5
VCC
--
4
RESET
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
VCC
MAX6854 MAX6855 MAX6856 MAX6858 MAX6860- MAX6869
RESET (MAX6854/MAX6856/MAX6858/ MAX6860/MAX6861 MAX6863/MAX6864/MAX6866/ MAX6867/MAX6869) RESET (MAX6855/MAX6862/MAX6865/ MAX6868)
RESET TIMEOUT GENERATOR
VCC
1.25V
10k MR (MAX6854/MAX6855/MAX6856/ MAX6861-MAX6869) WDI (MAX6864-MAX6869) WATCHDOG TRANSITION DETECTOR WATCHDOG TIMER CT (MAX6861/MAX6862/MAX6863)
GND
Figure 1. Functional Diagram
VTH VCC tRP tRP
tMRD RESET*
tRD
tMPW MR
*RESET IS THE INVERSE OF RESET.
Figure 2. RESET Timing Relationship 10 ______________________________________________________________________________________
Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
VCC WDI OV VCC RESET* OV tWDI tWD tRP
*RESET IS THE INVERSE OF RESET.
Figure 3. Detailed Watchdog Input Timing Relationship
Detailed Description
RESET/RESET Output
A P's reset input starts the P in a known state. The MAX6854/MAX6855/MAX6856/MAX6858/MAX6860- MAX6869 P supervisory circuits assert a reset to prevent code-execution errors during power-up, power-down, and brownout conditions. The MAX6854/MAX6855/MAX6856/ MAX6858/MAX6860-MAX6869 reset output is guaranteed to be valid for VCC down to 1.1V. Whenever VCC falls below the reset threshold, the reset output asserts low for RESET and high for RESET. Once V CC exceeds the reset threshold, an internal timer keeps the reset output asserted for the specified reset timeout period, then after this interval the reset output deasserts (see Figure 2).
Watchdog Input
The MAX6864-MAX6869's watchdog timer circuitry monitors the P's activity. If the P does not toggle (low-to-high or high-to-low) the watchdog input (WDI) within the watchdog timeout period (tWDI), reset asserts for the reset timeout period (tRP). The internal timer is cleared when reset asserts, when manual reset is asserted, or by a rising or falling edge on WDI. The watchdog input detects pulses as short as 150ns. While reset is asserted the watchdog timer does not count. As soon as reset deasserts, the watchdog timer resumes counting (Figure 3).
Applications Information
Selecting the Reset Timeout Period
The reset timeout period for the MAX6854/MAX6855/ MAX6856/MAX6858/MAX6860/MAX6864-MAX6869 is fixed (see Table 4). The MAX6861/MAX6862/MAX6863 feature a reset timeout select input, CT. Connect CT according to Table 1 to select between the available 10ms and 150ms (min) reset timeout periods. The timeout period can be changed while a reset timeout period is in progress, but will not update until the reset timeout period has expired.
Manual Reset Input
Many P-based products require manual reset capability, allowing the operator, a test technician, or external logic circuitry to initiate a reset. The MAX6854/ MAX6855/MAX6856/MAX6861-MAX6869 feature an MR input. A logic low on MR asserts a reset. Reset remains asserted while MR is low and for the timeout period, tRP, after MR returns high. The devices provide an internal 10k pullup from MR to VCC. Leave MR unconnected or connect to VCC if unused. MR can be driven with CMOS logic levels or with open-drain/collector outputs. Connect a normally open momentary switch from MR to GND to implement a manual reset function; external debounce circuitry is not required. If MR is driven by 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.
Table 1. MAX6861/MAX6862/MAX6863 Reset Timeout Period Selection
CT CONNECTION LOW HIGH MIN 10 150 TYP 15 225 MAX 25 300 UNITS ms
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
Transient Immunity
In addition to issuing a reset to the P during power-up, power-down, and brownout conditions, the MAX6854/ MAX6855/MAX6856/MAX6858/MAX6860-MAX6869 are relatively immune to short-duration supply transients, or glitches. The Maximum VCC Transient Duration vs. Reset Threshold Overdrive graph in the Typical Operating Characteristics shows this relationship. The area below the curve of the graph is the region in which these devices typically do not generate a reset pulse. This graph was generated using a falling pulse applied to VCC, starting 100mV above the actual reset threshold, VTH, and ending below this threshold (resetthreshold overdrive). As the magnitude of the transient increases, the maximum allowable pulse width decreases. Typically, a 100mV VCC transient duration of 40s or less does not cause a reset. open-drain output to level-shift from the monitored supply to reset circuitry powered by another supply voltage. Keep in mind that as the supervisor's VCC decreases, so does the IC's ability to sink current at RESET.
Ensuring a Valid RESET Down to VCC = 0V (Push-Pull RESET)
When VCC falls below 1.1V, RESET's current-sinking capability declines drastically. The high-impedance CMOS logic inputs connected to RESET can drift to undetermined voltages. This presents no problems in most applications, since most Ps and other circuitry do not operate with VCC below 1.1V. In those applications where RESET must be valid down to 0, add a pulldown resistor between RESET and GND for the MAX6854/MAX6858/MAX6861/MAX6864/ MAX6867 push-pull outputs. The resistor sinks any stray leakage currents, holding RESET low (Figure 5). Choose a pulldown resistor that accommodates leakages, such that RESET is not significantly loaded and is capable of pulling to GND. The external pulldown cannot be used with the open-drain reset outputs.
Interfacing to Other Voltages for Logic Compatibility
The open-drain RESET output can be used to interface to a P with other logic levels. As shown in Figure 4, the open-drain output can be connected to voltages from 0 to 5.5V. Generally, the pullup resistor connected to RESET connects to the supply voltage that is being monitored at the IC's VCC input. However, some systems use the
Watchdog Software Considerations
One way to help the watchdog timer monitor software execution more closely is to set and reset the watchdog
1.8V
3.3V
VCC
VCC VCC
MAX6856 MAX6860 MAX6863 MAX6866 MAX6869
RESET N
100k VCC
RESET
P
MAX6854 MAX6858 MAX6861 MAX6864 MAX6867
RESET 2M
GND
GND
GND
Figure 4. Interfacing with Other Voltage Levels
Figure 5. Ensuring RESET Valid to VCC = Ground
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer
input at different points in the program, rather than pulsing the watchdog input high-low-high or low-highlow. This technique avoids a stuck loop, in which the watchdog timer would continue to be reset inside the loop, keeping the watchdog from timing out. Figure 6 shows an example of a flow diagram where the I/O driving the watchdog input is set high at the beginning of the program, set low at the beginning of every subroutine or loop, then set high 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, causing a reset or interrupt to be issued.
MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
Table 2. Threshold Suffix Guide
SUFFIX 46 45 44 43 42 41 40 39 38 37 36 35 34 VCC THRESHOLD FALLING MIN 4.509 4.388 4.266 4.193 4.095 3.998 3.900 3.802 3.705 3.608 3.510 3.413 3.315 3.218 3.120 2.998 2.925 2.852 2.730 2.633 2.559 2.438 2.340 2.255 2.180 2.133 2.048 1.950 1.853 1.755 1.623 1.536 TYP 4.625 4.500 4.375 4.300 4.200 4.100 4.000 3.900 3.800 3.700 3.600 3.500 3.400 3.300 3.200 3.075 3.000 2.925 2.800 2.700 2.625 2.500 2.400 2.313 2.235 2.188 2.100 2.000 1.900 1.800 1.665 1.575 MAX 4.741 4.613 4.484 4.408 4.305 4.203 4.100 3.998 3.895 3.793 3.690 3.588 3.485 3.383 3.280 3.152 3.075 2.998 2.870 2.768 2.691 2.563 2.460 2.371 2.290 2.243 2.153 2.050 1.948 1.845 1.707 1.614 V UNITS
START
33 32 31
SET WDI HIGH PROGRAM CODE
30 29 28 27 26 25
SUBROUTINE OR PROGRAM LOOP SET WDI LOW
24 23 225 22 21 20
RETURN
19 18 17 16
Figure 6. Watchdog Flow Diagram
Table 3. Watchdog Timeout
SUFFIX S L WATCHDOG TIMEOUT PERIOD MIN 1.5 95 TYP 3.3 209 MAX 7.75 487 UNITS s
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
Table 4. Reset Timeout Periods
TIMEOUT OPTION D1 D2 D3 D4 D5 D6 RESET TIMEOUT PERIODS MIN 10 40 150 1200 300 600 TYP 15 60 225 1800 450 900 MAX 25 80 300 2400 600 1200 ms UNITS
Ordering Information (continued)
PART MAX6856UK_ _D_-T MAX6858UK_ _D_-T MAX6860UK_ _D_-T MAX6861UK_ _-T MAX6862UK_ _-T MAX6863UK_ _-T MAX6864UK_ _D_ _-T MAX6865UK_ _D_ _-T MAX6866UK_ _D_ _-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 PIN-PACKAGE 5 SOT23-5 5 SOT23-5 5 SOT23-5 5 SOT23-5 5 SOT23-5 5 SOT23-5 5 SOT23-5 5 SOT23-5 5 SOT23-5 5 SOT23-5 5 SOT23-5
Table 5. Standard Versions
PART MAX6854UK16D3 MAX6854UK23D3 MAX6854UK26D3 MAX6854UK29D3 MAX6854UK31D3 MAX6856UK16D3 MAX6856UK23D3 MAX6856UK26D3 MAX6856UK29D3 MAX6856UK31D3 MAX6861UK17 MAX6861UK225 MAX6861UK26 MAX6861UK29 MAX6862UK17 MAX6862UK225 MAX6862UK26 MAX6862UK29 MAX6863UK17 MAX6863UK225 MAX6863UK26 MAX6863UK29 MAX6864UK16D3S MAX6864UK23D3S MAX6864UK26D3S MAX6864UK29D3S MAX6864UK31D3S MAX6866UK16D3S MAX6866UK23D3S MAX6866UK26D3S MAX6866UK29D3S MAX6866UK31D3S TOP MARK AEFS AEFY AEFZ AEGA AEGB AEGR AEGS AEGT AEGU AEGV AEKO AEKS AEKP AEKQ AEOS AEOT AEOU AEOV AEOW AEOX AEOY AEOZ AEGC AEGD AEGE AEGF AEGG AEGW AEGX AEGY AEFT AEGZ
MAX6867UK_ _D_ _-T MAX6868UK_ _D_ _-T
MAX6869UK_ _D_ _-T -40C to +85C 5 SOT23-5 Insert reset threshold suffix (see Table 2, Threshold Suffix Guide) after UK. Insert the number corresponding to the desired reset timeout period (see Table 4, Reset Timeout Period) after D. Insert the letter corresponding to the desired watchdog timeout period (S or L, see Table 3) into the blank following the reset timeout period suffix for the MAX6864-MAX6869.
Note: Sample stock is generally held on standard versions only (see Table 5, Standard Versions Table). Standard versions have an order increment of 2500 pieces. Nonstandard versions have an order increment of 10,000 pieces. Contact factory for availability of nonstandard versions.
14
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer
Pin Configurations
TOP VIEW
MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
RESET 1 (RESET) GND 2
5
VCC
I.C. 1
5
VCC
CT 1
5
VCC
MAX6854 MAX6855 MAX6856
4 GND
I.C. 2
MAX6858 MAX6860
4 RESET
GND 2
MAX6861 MAX6862 MAX6863
4 RESET (RESET)
MR 3
GND 3
MR 3
SOT23
( ) MAX6855 ONLY
SOT23
SOT23
( ) MAX6862 ONLY
RESET 1 (RESET) GND 2
5
VCC
WDI 1
5
VCC
MAX6864 MAX6865 MAX6866
4 WDI
GND 2
MAX6867 MAX6868 MAX6869
4 RESET (RESET)
MR 3
MR 3
SOT23
( ) MAX6865 ONLY
SOT23
( ) MAX6868 ONLY
______________________________________________________________________________________
15
Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
Selector Guide
RESET OUTPUT PART MAX6854 MAX6855 MAX6856 MAX6858 MAX6860 MAX6861 MAX6862 MAX6863 MAX6864 MAX6865 MAX6866 MAX6867 MAX6868 MAX6869 PUSH-PULL ACTIVE LOW -- -- -- -- -- -- -- -- -- PUSH-PULL ACTIVE HIGH -- -- -- -- -- -- -- -- -- -- OPEN-DRAIN ACTIVE LOW -- -- -- -- -- -- -- -- -- MR -- -- WDI -- -- -- -- -- -- -- -- CT -- -- -- -- -- -- -- -- -- -- --
Chip Information
TRANSISTOR COUNT: 2848 PROCESS: BiCMOS
16
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Nanopower P Supervisory Circuits with Manual Reset and Watchdog Timer
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
MAX6854/MAX6855/MAX6856/MAX6858/MAX6860-MAX6869
PACKAGE OUTLINE, SOT-23, 5L
21-0057
E
1 1
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 ____________________ 17 (c) 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
SOT-23 5L .EPS

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