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MAX6455 Datasheet(PDF) 6 Page - Maxim Integrated Products |
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MAX6455 Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 10 page µP Supervisors with Separate VCC Reset and Manual Reset Outputs 6 _______________________________________________________________________________________ Detailed Description Reset Output The reset output is typically connected to the reset input of a microprocessor (µP). A µP’s reset input starts or restarts the µP in a known state. The MAX6453– MAX6456 µP supervisory circuits provide the reset logic to prevent code-execution errors during power- up, power-down and brownout conditions (see the Typical Operating Circuit). RESET changes from high to low whenever the moni- tored voltage (RSTIN or VCC) drops below the reset threshold voltages. When VRSTIN and VCC exceed their respective reset threshold voltages, RESET remains low for the reset timeout period, and then goes high. RESET changes from high to low after MR input is held low for the 3.36s (typ) setup period and deasserts 140ms (min) after MR deasserts. RESET is guaranteed to be in the proper output logic state for VCC inputs ≥ 1V. For applications requiring valid reset logic when VCC is less than 1V, see the Ensuring a Valid RESET Output Down to VCC = 0V section. Manual Reset The MAX6453/MAX6454 contain a manual reset output ( MROUT) that asserts low immediately after driving MR low and remains low for the reset timeout period after MR goes high (Figure 1). The pushbutton manual reset has no effect on the RESET output. MROUT output can be used to drive an NMI (nonmaskable interrupt) on the processor to save valuable data. The MAX6455/MAX6456’s MROUT is asserted immedi- ately upon driving MR low. Driving MR low for longer than the 3.36s (typ) setup period asserts RESET. When MR is deasserted, MROUT and RESET remain asserted low for the reset timeout period after MR goes high (Figure 2). Adjustable Input Voltage (RSTIN) The MAX6453–MAX6456 monitor the voltage on RSTIN using an adjustable reset threshold set with an external resistor voltage divider (Figure 3). Use the following for- mula to calculate the externally monitored voltage (VMON-TH): VMON-TH = VTH-RSTIN ✕ (R1 +R2) / R2 where VMON_TH is the desired reset threshold voltage and VTH-RSTIN is the reset input threshold (0.63V). Resistors R1 and R2 can have very high values to mini- mize current consumption due to low leakage currents. Set R2 to some conveniently high value (250k Ω, for example) and calculate R1 based on the desired reset threshold voltage, using the following formula: R1 = R2 ✕ (VMON_TH / VTH - 1) Ω 210ms MROUT RESET MR LONG SETUP PERIOD, 3.36s Figure 2. MAX6455/MAX6456 Timing Diagram 210ms MROUT MR Figure 1. MAX6453/MAX6454 Timing Diagram |
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