SC70, Single/Dual Low-Voltage, Low-Power µP Reset CircuitsMAX6381–MAX6390
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
(NO LOAD)
POWER-DOWN RESET DELAY
vs. TEMPERATURE
NORMALIZED RESET TIMEOUT PERIOD
8SUPPLY CURRENT (µA)
76543210
41POWER-DOWN RESET DELAY (µs)
39373533312927
1.061.041.021.000.980.960.94
-40-25-105203550658095110125
TEMPERATURE (°C)
25
-40-25-10520
3550658095110125
TEMPERATURE (°C)
-40-25-105203550658095110125
TEMPERATURE (°C)
NORMALIZED RESET THRESHOLD
vs. TEMPERATURE
MAX6381/90 toc04
OUTPUT VOLTAGE LOWvs. SINK CURRENT
OUTPUT VOLTAGE HIGHvs. SOURCE CURRENT
1.020NORMALIZED RESET
THRESHOLD1.0151.0101.0051.0000.9950.9900.985
1.21.00.8VOL (V)
0.6
0.40.200
3
6ISINK (mA)
93.02.52.0VOH (V)
1.51.00.500
250
500
750
1000
1250
0.990
-40-25-105203550658095110125
TEMPERATURE (°C)
12
1500
ISOURCE (µA)
MAXIMUM TRANSIENT DURATIONvs. RESET COMPARATOR OVERDRIVE
RESET IN TO RESET DELAY
vs. TEMPERATURE
5.35.1RESET IN DELAY (µs)
4.94.74.54.34.13.93.73.5
MAX6381/90 toc08
500MAXIMUM TRANSIENT DURATION (µs)
45040035030025020015010050
1
10
100
5.5
1000-40-25-105203550658095110125
TEMPERATURE (°C)
RESET COMPARATOR OVERDRIVE, VTH - VCC (mV)
4______________________________________________________________________________________
MAX6381/90 toc03
9
NORMALIZED POWER-UP RESET TIMEOUT
vs. TEMPERATURE
1.08
43
SC70, Single/Dual Low-Voltage, Low-Power µP Reset Circuits
_______________________________________________________________________________________5
MAX6381–MAX6390
SC70, Single/Dual Low-Voltage, Low-Power µP Reset CircuitsMAX6381–MAX6390
Detailed Description
RESET Output
A µP reset input starts the µP in a known state. TheseµP supervisory circuits assert reset to prevent codeexecution errors during power-up, power-down, orbrownout conditions.
Reset asserts when VCCis below the reset threshold;once VCCexceeds the reset threshold, an internal timerkeeps the reset output asserted for the reset timeoutperiod. After this interval, reset output deasserts. Resetoutput is guaranteed to be in the correct logic state forVCC≥1V.
Manual Reset Input (MAX6384/MAX6385/MAX6386/MAX6390)
Many µP-based products require manual reset capabil-ity, allowing the operator, a test technician, or externallogic circuitry to initiate a reset. A logic low on MRasserts reset. Reset remains asserted while MRis low,and for the reset active timeout period (tRP) after MRreturns high. This input has an internal 63k pullupresistor (1.35k for MAX6390), so it can be left uncon-nected if it is not used. MRcan be driven with TTL orCMOS logic levels, or with open-drain/collector outputs.Connect a normally open momentary switch from MRtoGND to create a manual-reset function; externaldebounce circuitry is not required. If MRis driven fromlong cables or if the device is used in a noisy environ-ment, connecting a 0.1µF capacitor from MRto GNDprovides additional noise immunity.
RESET IN Comparator
(MAX6387/MAX6388/MAX6389)
RESET IN is compared to an internal +1.27V reference.If the voltage at RESET IN is less than 1.27V, resetasserts. Use the RESET IN comparator as a user-adjustable reset detector or as a secondary power-sup-ply monitor by implementing a resistor-divider at RESETIN (shown in Figure 1). Reset asserts when either VCCor RESET IN falls below its respective threshold volt-age. Use the following equation to set the threshold:
VINTH= VTHRST (R1/R2 + 1)where VTHRST= +1.27V. To simplify the resistor selec-tion, choose a value of R2 and calculate R1:
R1 = R2 [(VINTH/VTHRST) - 1]
Since the input current at RESET IN is 50nA (max),large values can be used for R2 with no significant lossin accuracy.
___________Applications Information
In addition to issuing a reset to the µP during power-up,power-down, and brownout conditions, theMAX6381–MAX6390 are relatively immune to short dura-tion negative-going VCCtransients (glitches).
The Typical Operating Characteristicssection shows theMaximum Transient Durations vs. Reset ComparatorOverdrive, for which the MAX6381–MAX6390 do notgenerate a reset pulse. This graph was generated using
Negative-Going VCCTransients
6_______________________________________________________________________________________
SC70, Single/Dual Low-Voltage, Low-Power µP Reset Circuits
MAX6381–MAX6390
not work with the open-drain outputs of theMAX6383/MAX6386/MAX6389/MAX6390. The resistorvalue used is not critical, but it must be small enoughnot to load the reset output when VCCis above the resetthreshold. For most applications, 100k is adequate.
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