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MAX6381XS33D4-T Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX6381XS33D4-T Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 11 page SC70, Single/Dual Low-Voltage, Low-Power µP Reset Circuits 6 _______________________________________________________________________________________ Detailed Description RESET Output A µP reset input starts the µP in a known state. These µP supervisory circuits assert reset to prevent code execution errors during power-up, power-down, or brownout conditions. Reset asserts when VCC is below the reset threshold; once VCC exceeds the reset threshold, an internal timer keeps the reset output asserted for the reset timeout period. After this interval, reset output deasserts. Reset output is guaranteed to be in the correct logic state for VCC ≥ 1V. Manual Reset Input (MAX6384/ MAX6385/MAX6386/MAX6390) Many µP-based products require manual reset capabil- ity, allowing the operator, a test technician, or external logic circuitry to initiate a reset. A logic low on MR asserts reset. Reset remains asserted while MR is low, and for the reset active timeout period (tRP) after MR returns high. This input has an internal 63k Ω pullup resistor (1.35k Ω for MAX6390), so it can be left uncon- nected if it is not used. MR can be driven with TTL or 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 if the device is used in a noisy environ- ment, connecting a 0.1µF capacitor from MR to GND provides 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, reset asserts. 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 RESET IN (shown in Figure 1). Reset asserts when either VCC or 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 loss in accuracy. ___________Applications Information Negative-Going VCC Transients In addition to issuing a reset to the µP during power-up, power-down, and brownout conditions, the MAX6381–MAX6390 are relatively immune to short dura- tion negative-going VCC transients (glitches). The Typical Operating Characteristics section shows the Maximum Transient Durations vs. Reset Comparator Overdrive, for which the MAX6381–MAX6390 do not generate a reset pulse. This graph was generated using Reset Thresholds (-40°C to +125°C) SUFFIX VTH (min) VTH (nom) VTH (max) 46 4.51 4.63 4.74 45 4.39 4.50 4.61 44 4.27 4.38 4.48 43 4.19 4.30 4.41 42 4.10 4.20 4.31 41 4.00 4.10 4.20 40 3.90 4.00 4.10 39 3.80 3.90 4.00 38 3.71 3.80 3.90 37 3.61 3.70 3.79 36 3.51 3.60 3.69 35 3.41 3.50 3.59 34 3.32 3.40 3.49 33 3.22 3.30 3.38 32 3.12 3.20 3.28 31 3.00 3.08 3.15 30 2.93 3.00 3.08 29 2.85 2.93 3.00 28 2.73 2.80 2.87 27 2.63 2.70 2.77 26 2.56 2.63 2.69 25 2.44 2.50 2.56 24 2.34 2.40 2.46 23 2.26 2.31 2.37 22 2.13 2.19 2.24 21 2.05 2.10 2.15 20 1.95 2.00 2.05 19 1.85 1.90 1.95 18 1.76 1.80 1.85 17 1.62 1.67 1.71 16 1.54 1.58 1.61 |
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