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MAX6333UR18D2-T Datasheet(PDF) 4 Page - Maxim Integrated Products |
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MAX6333UR18D2-T Datasheet(HTML) 4 Page - Maxim Integrated Products |
4 / 6 page 3-Pin, Ultra-Low-Voltage, Low-Power µP Reset Circuits 4 _______________________________________________________________________________________ ______________Applications Information Interfacing to µPs with Bidirectional Reset Pins Since the RESET output on the MAX6334 is open-drain, this device interfaces easily with µPs that have bidirec- tional reset pins, such as the Motorola 68HC11. Connecting the µP supervisor’s RESET output directly to the microcontroller’s (µC’s) RESET pin with a single pull-up resistor allows either device to assert reset (Figure 1). Negative-Going VCC Transients In addition to issuing a reset to the µP during power-up, power-down, and brownout conditions, these devices are relatively immune to short-duration, negative-going VCC transients (glitches). The Typical Operating Characteristics show the Maximum Transient Duration vs. Reset Comparator Overdrive graph. The graph shows the maxi- mum pulse width that a negative-going VCC transient may typically have without issuing a reset signal. As the ampli- tude of the transient increases, the maximum allowable pulse width decreases. Ensuring a Valid Reset Output Down to VCC = 0 When VCC falls below 1V and approaches the minimum operating voltage of 0.7V, push/pull-structured reset sinking (or sourcing) capabilities decrease drastically. High-impedance CMOS-logic inputs connected to the RESET pin can drift to indeterminate voltages. This does not present a problem in most cases, since most µPs and circuitry do not operate at VCC below 1V. For the MAX6333, where RESET must be valid down to 0, adding a pull-down resistor between RESET and GND removes stray leakage currents, holding RESET low (Figure 2a). The pull-down resistor value is not critical; 100k Ω is large enough not to load RESET and small enough to pull it low. For the MAX6332, where RESET must be valid to VCC = 0, a 100kΩ pull-up resistor between RESET and VCC will hold RESET high when VCC falls below 0.7V (Figure 2b). Since the MAX6334 has an open-drain, active-low out- put, it typically uses a pull-up resistor. With this device, RESET will most likely not maintain an active condition, but will drift to a non-active level due to the pull-up resistor and the reduced sinking capability of the open- drain device. Therefore, this device is not recommend- ed for applications where the RESET pin is required to be valid down to VCC = 0. VCC VCC GND MAX6334 RESET VCC GND RESET INPUT MOTOROLA 68HCXX µP * Factory-trimmed reset thresholds are available in approximately 100mV increments, with a ±1.8% room-temperature variance. TA = +25°C TA = -40°C to +85°C MIN TYP MAX MIN MAX MAX633_UR25D_ 2.46 2.50 2.55 2.43 2.58 MAX633_UR24D_ 2.36 2.40 2.44 2.33 2.47 MAX633_UR23D_ 2.26 2.30 2.34 2.23 2.37 MAX633_UR22D_ 2.16 2.20 2.24 2.13 2.27 MAX633_UR21D_ 2.06 2.10 2.14 2.04 2.16 MAX633_UR20D_ 1.96 2.00 2.04 1.94 2.06 MAX633_UR19D_ 1.87 1.90 1.93 1.84 1.96 MAX633_UR18D_ 1.77 1.80 1.83 1.75 1.85 MAX633_UR17D_ 1.67 1.70 1.73 1.65 1.75 MAX633_UR16D_ 1.57 1.60 1.63 1.55 1.65 RESET- THRESHOLD SUFFIX Table 1. Factory-Trimmed Reset Thresholds* Figure 1. Interfacing to µPs with Bidirectional Reset Pins Figure 2. Ensuring Reset Valid Down to VCC = 0 VCC GND MAX6333 RESET 100k (a) VCC GND MAX6332 RESET 100k* (b) *ASSUMES HIGH-Z RESET INPUT TO THE µP |
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