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MAX6391KA26-T Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX6391KA26-T Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 9 page Dual-Voltage µP Supervisory Circuits with Sequenced Reset Outputs _______________________________________________________________________________________ 7 Applications Information Selecting the Reset Timeout Capacitor The RESET2 delay may be adjusted by the user with an external capacitor connected from the CSRT pin to ground. The MAX6391 includes a 600nA current source that is switched to CCSRT to create a voltage ramp. The voltage ramp is compared to the internal 1.25V refer- ence to set the RESET2 delay period. The period is cal- culated by: ∆t = C ✕ ∆V/I where ∆V = 1.25V, I = 600nA, and C is the external capacitor. Simplifying, tRP = 2.08 ✕ 106 s / F ✕ CCSRT For CCSRT = 1500pF, tRP = 3.1ms A fixed internal 140ms (min) reset delay time for RESET2 may be chosen by connecting the CSRT pin to VCC. The VCC to CSRT connection disables the voltage ramp and enables a separate fixed delay counter chain. The MAX6391 internally determines the CSRT connection and provides the proper timing setup. In all cases, RESET IN2 acts as the slave supply. VCC can assert the RESET2 output but RESET IN2 will have no effect on the RESET1 output. Monitoring Voltages Other Than VCC An external resistive-divider network is required at RESET IN2 for most applications. The divider resistors, R3 and R4, may be calculated by the following formula: VRST = VTH2 ✕ (R3 + R4)/R4 where VTH2 = 625mV (internal reference voltage) and VRST is the desired reset threshold voltage. R4 may be set to a conveniently high value (500k Ω for example, to minimize current consumption) and the equation may be solved for R3 by: R3 = R4 ✕ (VRST/VTH2 - 1) For single-supply operations requiring two reset out- puts (RESET1 before RESET2), connect RESET IN2 directly to VCC and adjust RESET2 timeout delay with CCRST as desired. Pullup Resistors The MAX6391 includes open-drain outputs for both RESET1 and RESET2. Two internal resistors, R1 and R2, of 47k Ω each are provided with internal connec- tions to RESET1 and RESET2. These resistors may be connected to the appropriate external voltage for inde- pendent VOH drive with no additional component requirements. The MAX6392 includes a manual reset option, MR, that replaces the R1 pullup resistor. The active-low manual reset input forces both RESET1 and RESET2 low. RESET2 is driven active before RESET1 in all cases (10µs typ). The resets follow standard reset timing specifications after the manual reset is released. The manual reset is internally pulled up to VCC through a 47k Ω resistor. 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 or RESET IN2 transients (glitches). The Typical Operating Characteristics show the Maximum Transient Duration vs. Reset Comparator Overdrive graph. The graph shows the maximum pulse width that a negative- going VCC transient may typically have without issuing a reset signal. As the amplitude of the transient increas- es, the maximum allowable pulse width decreases. PART NUMBER NOMINAL THRESHOLD (V) TOP MARK MAX6391KA46 4.63 AAHJ MAX6391KA44 4.38 AAHK MAX6391KA31 3.08 AAHL MAX6391KA29 2.93 AAHM MAX6391KA26 2.63 AAHN MAX6391KA23 2.32 AAHO MAX6391KA22 2.19 AAHP MAX6391KA17 1.67 AAHQ MAX6391KA16 1.58 AAHR MAX6392KA46 4.63 AAHS MAX6392KA44 4.38 AAHT MAX6392KA31 3.08 AAHU MAX6392KA29 2.93 AAHV MAX6392KA26 2.63 AAHW MAX6392KA23 2.32 AAHX MAX6392KA22 2.19 AAHY MAX6392KA17 1.67 AAHZ MAX6392KA16 1.58 AAIA Selector Guide Standard versions in bold face. Samples are typically available for standard versions. Contact factory for availability. |
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