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19-2625; Rev 1; 2/03
Ultra-Low-Voltage P Reset Circuits and Voltage Detectors
General Description
The MAX6841-MAX6845 microprocessor (P) supervisory circuits monitor ultra-low-voltage power supplies in P and digital systems. They provide excellent circuit reliability at low cost by eliminating external components and adjustments when used with +0.9V to +1.5V systems. Factory-trimmed reset thresholds are available for the MAX6841/MAX6842. The MAX6843/ MAX6844/MAX6845 provide a RESET IN input, allowing the user to externally adjust the reset threshold. The MAX6841-MAX6845 family features a debounced manual reset input (MR). The reset comparator is designed to ignore fast transients on VCC. The MAX6841-MAX6845 assert a reset signal whenever the VCC supply voltage declines below a preset or adjustable threshold or whenever manual reset (MR) is asserted. Reset remains asserted for a fixed timeout delay after VCC has risen above the reset threshold and when manual reset is deasserted. Five timeout periods are available for each part: 150s (voltage detector version), 1.5ms, 30ms, 210ms, and 1.68s (typ). The MAX6841/MAX6843 have an active-low push-pull reset output. The MAX6841/MAX6842/MAX6844 have an active-high push-pull reset output, and the MAX6842/MAX6845 have an active-low open-drain reset output. The active-low open-drain reset output requires a pullup resistor that can be connected to a voltage from 0 to VCC. The low supply current (5.7A) and small package (SOT23-5) make the MAX6841-MAX6845 ideal for use in portable equipment.
Features
o Factory-Set Reset Threshold Voltages for Monitoring Supplies from 0.9V to 1.5V (MAX6841/MAX6842) o Adjustable Threshold RESET IN (MAX6843/MAX6844/MAX6845) o Low Power Consumption: 5.7A (typ) o 2.5% Reset Threshold Accuracy Over Temperature o Five Timeout Periods: 150s (Voltage Detector Version), 1.5ms, 30ms, 210ms, and 1.68s o Available in Three Output Configurations Push-Pull RESET Push-Pull RESET Open-Drain RESET o Guaranteed Reset Valid to VCC = 0.55V (Active Low) o Manual Reset Input o Immune to Short VCC Transients o Space-Saving 5-Pin SOT23 Package
MAX6841-MAX6845
Ordering Information
PART MAX6841_UKD_-T MAX6842_UKD_-T MAX6843UKD_-T MAX6844UKD_-T MAX6845UKD_-T TEMP RANGE -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
Applications
Computers Controllers Intelligent Instruments Critical P and C Power Monitoring Portable/Battery-Powered Equipment Telecom/Networking Equipment Basestations Servers/Workstations
Note: Insert desired suffix letter (from the Threshold Suffix Guide and the Active Timeout Period tables) into the blanks to complete the part number. For example, the MAX6842GUKD1 has a reset threshold of 1.11V and a typical reset timeout period of 1.5ms. Sample stock is generally available on standard versions only (see the Standard Versions table). Standard versions require a minimum order increment of 2.5k units. Nonstandard versions must be ordered in 10k-unit increments. Contact factory for availability. All parts are offered in tape-and-reel only.
Pin Configurations
TOP VIEW
RESET 1 GND 2 5 VCC RESET 1 (RESET) GND 2 4 MR RESET IN 3 5 VCC
MAX6841 MAX6842
MAX6843 MAX6844 MAX6845
4 MR
Selector Guide and Typical Operating Circuit appear at end of data sheet.
RESET 3
SOT23-5
SOT23-5
( ) ARE FOR 6844
________________________________________________________________ Maxim Integrated Products
1
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Ultra-Low-Voltage P Reset Circuits and Voltage Detectors MAX6841-MAX6845
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND) VCC .......................................................................-0.3V to +6V MR, RESET IN, RESET (open-drain).........................-0.3V to +6V Push-Pull RESET and RESET .....................-0.3V to (VCC + 0.3V) Input Current (all pins) ........................................................20mA Output Current (RESET, RESET).........................................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 = +0.55V to +1.8V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Supply Voltage Range SYMBOL VCC CONDITIONS MAX6843/MAX6845 MAX6841/MAX6842/MAX6844 (Note 2) VCC = 0.9V, no load, reset not asserted Supply Current ICC VCC = 1.5V, no load, reset not asserted VCC = 1.8V, no load, reset not asserted I Reset Threshold (VCC Falling) H VTH G F E D, TA = 0C to +85C RESET IN Threshold RESET IN Leakage Current Reset Threshold Hysteresis VCC or RESET IN to Reset Delay VRSTIN IRSTIN VHYS VCC falling, step signal from (VTH + 10%) to (VTH - 10%) within 1s D0 (voltage detector) D1 Reset Active Timeout Period tRP D2 D3 D4 MR Input Voltage (Note 3) MR Minimum Input Pulse Width MR Glitch Rejection MR to Reset Delay MR Pullup Resistance to VCC VIL VIH MR driven from VCC to 0 (Note 3) MR driven from VCC to 0 (Note 3) MR driven from VCC to 0 (Note 3) 10 0.7 x VCC 1 150 500 20 26 1 20 140 1120 MAX6843/MAX6844/MAX6845 (Note 3) 1.350 1.275 1.080 1.020 0.810 0.765 181.2 -25 0.75 150 0.15 1.5 30 210 1680 2 40 280 2240 0.3 x VCC V s ns ns k ms MIN 0.55 0.75 5.7 7.3 8.1 1.388 1.313 1.110 1.050 0.833 0.788 187.4 TYP MAX 1.80 1.80 20 20 20 1.425 1.350 1.140 1.080 0.855 0.810 191.5 +25 mV nA %VTH s V A UNITS V
2
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Ultra-Low-Voltage P Reset Circuits and Voltage Detectors
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +0.55V to +1.8V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Open-Drain RESET Output Voltage Open-Drain RESET Output Leakage Current SYMBOL VOL ILKG VOL Push-Pull RESET Output Voltage VOH CONDITIONS VCC 0.55V, ISINK = 10A, reset asserted VCC 0.83V, ISINK = 80A, reset asserted VCC > VTH, reset not asserted VCC 0.55V, ISINK = 10A, reset asserted VCC 0.83V, ISINK = 80A, reset asserted VCC 0.83V, ISOURCE = 40A, reset not asserted VCC 0.75V, ISOURCE = 10A, reset asserted VOH Push-Pull RESET Output Voltage VOL VCC 0.83V, ISOURCE = 40A, reset asserted VCC 0.83V, ISINK = 80A, reset not asserted 0.8 x VCC 0.8 x VCC 0.8 x VCC 0.2 x VCC V MIN TYP MAX 0.2 x VCC 0.2 x VCC 1 0.2 x VCC 0.2 x VCC V UNITS V A
MAX6841-MAX6845
Note 1: 100% production tested at +25C. Overtemperature limits are guaranteed by design. Note 2: The active-low output RESET has VCC(MIN) = 0.55V (MAX6841/MAX6842). Note 3: For VCC > 0.788V, TA = 0C to +85C, and for VCC > 0.833V, TA = -40C to +85C.
Typical Operating Characteristics
(VCC = 1.5V, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX6841-45 toc01
POWER-DOWN RESET DELAY vs. TEMPERATURE
MAX6841-45 toc02
NORMALIZED RESET TIMEOUT PERIOD vs. TEMPERATURE
NORMALIZED RESET TIMEOUT PERIOD
MAX6841-45 toc03
9 8 SUPPLY CURRENT (A) 7 6 5 4 3 2 1 0 -40 -20 0 20 40 60 80 TEMPERATURE (C) VCC = 1.5V VCC = 0.9V VCC = 1.8V
350 POWER-DOWN RESET DELAY (s) 300 250 200 150 100 VOD = 100mV 50 VOD = OVERDRIVE (mV) 0 -40 -20 0 20 40 60 80 TEMPERATURE (C) VOD = 10mV VOD = 20mV
1.06 1.04 1.02 1.00 0.98 0.96 0.94 -40 -20 0 20 40 60 80 TEMPERATURE (C) D4 OPTION
D2 OPTION D3 OPTION
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Ultra-Low-Voltage P Reset Circuits and Voltage Detectors MAX6841-MAX6845
Typical Operating Characteristics (continued)
(VCC = 1.5V, TA = +25C, unless otherwise noted.)
NORMALIZED VCC RESET THRESHOLD vs. TEMPERATURE
MAX6841-45 toc04
NORMALIZED RESET IN THRESHOLD vs. TEMPERATURE
NORMALIZED RESET IN THRESHOLD
MAX6841-45 toc05
POWER-UP/POWER-DOWN CHARACTERISTICS (MAX6843AUKD3)
MAX6841-45 toc06
1.015 VTH = 0.833V NORMALIZED VCC RESET THRESHOLD 1.010 1.005 1.000 0.995 0.990 0.985 -40 -20 0 20 40 60 80 TEMPERATURE (C)
1.015 1.010 1.005 1.000 0.995 0.990 0.985 -40 -20 0 20 40 60 80
VCC 1V/div
RESET 1V/div
200ms/div
TEMPERATURE (C)
Pin Description
FUNCTION
PIN MAX6841 MAX6842 MAX6843 MAX6845 MAX6844 NAME
1
--
-- RESET
Push-Pull (MAX6841) or Open-Drain (MAX6842) Active-Low Reset Output. RESET changes 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 is released high. Push-Pull (MAX6843) or Open-Drain (MAX6845) Active-Low Reset Output. RESET changes from high to low when RESET IN drops below the 187.4mV reset threshold (referenced to VCC) or MR is pulled low. RESET remains low for the reset timeout period after RESET IN exceeds the reset threshold and MR is released high. Ground Push-Pull Active-High Reset Output. RESET changes from low to high when VCC input 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 is released high. Push-Pull Active-High Reset Output. RESET changes from low to high when the RESET IN input drops below the 187.4mV reset threshold (referenced to VCC). RESET remains high for the reset timeout period after RESET IN exceeds the reset threshold.
--
1
--
2
2
2
GND
3
--
-- RESET
--
--
1
--
3
3
Adjustable Reset Input. High-impedance input for reset comparator. Connect this pin to an external resistive-divider network to set the reset threshold voltage; the RESET IN typical threshold is 187.4mV (referenced to VCC). The MAX6843/MAX6844/ MAX6845 assert a reset signal when the VCC to RESET IN differential falls below its threshold voltage. MR VCC Active-Low Manual Reset Input. Internal 20k pullup to VCC. Pull low to force a reset. Reset remains active as long as MR is low and for the reset timeout period after MR goes high. Leave unconnected or connect to VCC if unused. Supply Voltage. Monitored supply for the MAX6841/MAX6842.
4 5
4 5
4 5
4
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Ultra-Low-Voltage P Reset Circuits and Voltage Detectors
Functional Diagrams
MR
MR
MAX6841-MAX6845
VCC MR PULLUP VREF MANUAL RESET DETECT MAX6841 MAX6842
VCC MR PULLUP VREF = 187.4mV RESET IN MANUAL RESET DETECT MAX6843 MAX6844 MAX6845
RESET TIMEOUT PERIOD
RESET OUTPUT
RESET RESET
RESET TIMEOUT PERIOD
RESET OUTPUT
RESET RESET
GND
GND
Detailed Description
Reset Output
A microprocessor's (P's) reset input starts the P in a known state. The MAX6841-MAX6845 assert a reset during power-up, power-down, and brownout conditions. When the VCC supply voltage falls below a preset threshold (MAX6841/MAX6842) or RESET IN falls below the adjustable threshold (MAX6843/MAX6844/MAX6845), reset asserts and stays asserted for a fixed timeout delay (Table 2) after VCC or RESET IN has risen above the reset threshold. The MAX6841-MAX6845 are available with five typical timeout options for each part: 150s (voltage detector), 1.5ms, 30ms, 210ms, and 1.68s. The MAX6841/MAX6842 have two reset outputs (RESET and RESET); one is the inverse of the other. The MAX6841 has one active-high push-pull output and one active-low push-pull output. The MAX6842 has one active-high push-pull output and one active-low opendrain output. The MAX6843 features an active-low push-pull output. The MAX6844 features an activehigh push-pull output, and the MAX6845 has an activelow open-drain output stage. Connect a pullup resistor from the open-drain RESET output to any voltage between 0 and 6V.
tion, connect a normally open momentary switch from MR to ground; 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 ground to provide additional noise immunity.
RESET IN
The MAX6843/MAX6844/MAX6845 feature a RESET IN input, which allows users to adjust the reset threshold voltage. The internal reference voltage is 187.4mV with respect to VCC. An external resistive-divider network can be used to set voltage monitoring thresholds, as shown in Figure 1. The resistive-divider network must be referenced to V CC . As V CC falls, the voltage at
VCC R1 VCC RESET IN R2
MAX6843 MAX6844 MAX6845
MR R1 = R2 VCC-TH -1 VREF GND
RESET (RESET)
Manual Reset Input
Many P-based systems require a manual reset capability, allowing the operator, a test technician, or external logic circuitry to initiate a reset. Reset remains asserted while MR is low, and for a fixed timeout delay after MR returns high. This input has an internal 20k pullup resistor, so it can be left open if it is not used. MR can be driven with CMOS logic level or with opendrain/collector outputs. To create a manual reset func-
( ) ARE FOR MAX6844
WHERE VREF = 187.4mV (WITH RESPECT TO VCC) AND VCC-TH IS THE VCC THRESHOLD.
Figure 1. Setting the Adjustable Threshold Externally 5
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Ultra-Low-Voltage P Reset Circuits and Voltage Detectors MAX6841-MAX6845
RESET IN decreases. The MAX6843/MAX6844/ MAX6845 assert a reset when the voltage at RESET IN falls below the RESET IN threshold (VRSTIN). The lowleakage current at RESET IN allows for relatively largevalue resistors to be used, which reduces power consumption. For example, for VCC-TH = 0.9V, if R2 = 100k, then R1 = 26.3k. most applications, because most P and other circuitry are inoperative with VCC lower than 0.55V. However, in applications in which RESET must be valid down to 0, adding a pulldown resistor to RESET causes any stray leakage currents to flow to ground, holding RESET low (Figure 3). R3's value is not critical; 200k is large enough not to load RESET and small enough to pull RESET to ground.
Applications Information
VCC Falling Transients The MAX6841-MAX6845 are relatively immune to shortduration falling V CC transients (glitches). Figure 2 shows typical transient duration vs. reset comparator overdrive, for which the MAX6841-MAX6845 do not generate a reset pulse. The graph was generated using a falling pulse applied to VCC, starting 0.1V above the actual reset threshold and ending below it by the magnitude indicated (reset comparator overdrive). The graph indicates the maximum pulse width that a falling VCC transient can have without causing a reset pulse. As the magnitude of the transient increases (goes further below the reset threshold), the maximum allowable pulse width decreases. A 0.1F bypass capacitor mounted as close as possible to the VCC pin provides additional transient immunity. Ensuring a Valid Reset Output Down to VCC = 0
When VCC falls below 0.55V, the MAX6841/MAX6843 push-pull RESET output no longer sinks current; it becomes an open circuit. Therefore, high-impedance CMOS-logic inputs connected to RESET can drift to undetermined voltages. This presents no problem in
MAXIMUM TRANSIENT DURATION vs. OVERDRIVE
600 MAXIMUM TRANSIENT DURATION (s) 550 500 450 400 350 300 250 200 150 100 1 10 OVERDRIVE VTH - VCC (mV) 100 RESET OCCURS ABOVE THIS LINE
VCC
MAX6841 MAX6843
RESET GND R3
Figure 3. RESET Valid to VCC = 0
A 200k pullup resistor to VCC is also recommended for the MAX6841/MAX6842/MAX6844 if push-pull RESET is required to remain valid for VCC 0.75V.
Interfacing to Ps with Bidirectional Reset Pins
Because the RESET output on the MAX6842/MAX6845 is open drain, these devices interface easily with Ps that have bidirectional reset pins. Connecting the P supervisor's RESET output directly to the P's RESET pin with a single pullup resistor allows either device to assert reset (Figure 4).
VCC VCC VCC
MAX6842 MAX6845
RESET GND RESET INPUT
P
GND
Figure 2. Maximum Transient Duration vs. Overdrive 6
Figure 4. Interfacing to Microprocessors with Bidirectional Reset I/0
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Ultra-Low-Voltage P Reset Circuits and Voltage Detectors MAX6841-MAX6845
0.9V VCC RPULLUP P RESET GND +5.0V
Table 1. Threshold Suffix Guide
SUFFIX RESET THRESHOLD (V) 1.388 1.313 1.110 1.050 0.833 0.788 I H G F E D
VCC
MAX6842 MAX6845
RESET GND
Table 2. Active Timeout Period Guide
Figure 5. Using the MAX6842/MAX6845 Open-Drain RESET Output with Multiple Supplies
SUFFIX D0 D1 RESET ACTIVE TIMEOUT PERIOD (ms) MIN -- 1 20 140 1120 TYP 0.15 1.5 30 210 1680 MAX -- 2 40 280 2240
Using the MAX6842/MAX6845 Open-Drain RESET Output with Multiple Supplies
Generally, the pullup connected to the MAX6842/ MAX6845 connects to the supply voltage being monitored at the IC's VCC pin. However, some systems use the open-drain output to level-shift from the monitored supply to reset circuitry powered by some other supply (Figure 5). Note that as the MAX6842/MAX6845's VCC decreases, so does the IC's ability to sink current at RESET. Also, with any pullup, RESET is pulled high as VCC decays toward 0. The voltage where this occurs depends on the pullup resistor value and the voltage to which it is connected.
D2 D3 D4
Table 3. Standard Versions
DEVICE MAX6841HUKD0 MAX6841HUKD3 MAX6841FUKD0 MAX6841FUKD3 MAX6841DUKD0 MAX6841DUKD3 MAX6842HUKD0 MAX6842HUKD3 MAX6842FUKD0 MAX6842FUKD3 MAX6842DUKD0 MAX6842DUKD3 MAX6843UKD0 MAX6843UKD3 MAX6844UKD0 MAX6844UKD3 MAX6845UKD0 MAX6845UKD3 TOP MARK AEDR AEDS AEDP AEDQ AEDN AEDO AEDX AEDY AEDV AEDW AEDT AEDU AEDZ AEAV AEEB AEEC AEAX AEAY
Chip Information
TRANSISTOR COUNT: 788 PROCESS: BiCMOS
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Ultra-Low-Voltage P Reset Circuits and Voltage Detectors MAX6841-MAX6845
Selector Guide
PART MAX6841 MAX6842 MAX6843 MAX6844 MAX6845 MANUAL RESET ADJUSTABLE RESET INPUT -- -- PUSH-PULL RESET -- -- -- PUSH-PULL RESET -- -- OPEN-DRAIN RESET -- -- --
Typical Operating Circuit
VIN 3.3V 0.9V DC/DC CONVERTER CORE SUPPLY VCC P I/O SUPPLY
MAX6842D/E
RESET PUSHBUTTON SWITCH MR GND RESET RESET GND
8
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Ultra-Low-Voltage P Reset Circuits and Voltage Detectors
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.)
MAX6841-MAX6845
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 _____________________ 9 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
SOT5L.EPS

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