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MAX6338-T Datasheet(PDF) 10 Page - Maxim Integrated Products |
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MAX6338-T Datasheet(HTML) 10 Page - Maxim Integrated Products |
10 / 14 page MAX6316–MAX6322 5-Pin µP Supervisory Circuits with Watchdog and Manual Reset 10 Maxim Integrated Applications Information Watchdog Input Current The WDI input is internally driven through a buffer and series resistor from the watchdog counter. For minimum watchdog input current (minimum overall power con- sumption), leave WDI low for the majority of the watch- dog timeout period. When high, WDI can draw as much as 160µA. Pulsing WDI high at a low duty cycle will reduce the effect of the large input current. When WDI is left unconnected, the watchdog timer is serviced within the watchdog timeout period by a low-high-low pulse from the counter chain. Negative-Going VCC Transients These supervisors are immune to short-duration, nega- tive-going VCC transients (glitches), which usually do not require the entire system to shut down. Typically, 200ns large-amplitude pulses (from ground to VCC) on the supply will not cause a reset. Lower amplitude puls- es result in greater immunity. Typically, a VCC transient that goes 100mV under the reset threshold and lasts less than 4µs will not trigger a reset. An optional 0.1µF bypass capacitor mounted close to VCC provides addi- tional transient immunity. Ensuring Valid Reset Outputs Down to VCC = 0V The MAX6316_/MAX6317H/MAX6318_H/MAX6319_H/ MAX6321HP/MAX6322HP are guaranteed to operate properly down to VCC = 1V. In applications that require valid reset levels down to VCC = 0V, a pulldown resistor to active-low outputs (push/pull and bidirectional only, Figure 8) and a pullup resistor to active-high outputs (push/pull only, Figure 9) will ensure that the reset line is valid while the reset output can no longer sink or source current. This scheme does not work with the open-drain outputs of the MAX6320/MAX6321/MAX6322. The resistor value used is not critical, but it must be large enough not to load the reset output when VCC is above the reset threshold. For most applications, 100k Ω is adequate. Watchdog Software Considerations (MAX6316/MAX6317/MAX6318/ MAX6320/MAX6321) One way to help the watchdog timer monitor software execution more closely is to set and reset the watchdog input at different points in the program, rather than pulsing the watchdog input high-low-high or low-high- low. This technique avoids a stuck loop, in which the watchdog timer would continue to be reset inside the loop, keeping the watchdog from timing out. VCC tWD tRP tRP tRST WDI RESET MAX6316/MAX6317 MAX6318/MAX6320 MAX6321 Figure 7. Watchdog Timing Relationship GND *THIS SCHEMATIC DOES NOT WORK ON THE OPEN-DRAIN OUTPUTS OF THE MAX6321/MAX6322. 100k Ω VCC VCC RESET MAX6317 MAX6318 MAX6319 MAX6321* MAX6322* Figure 9. Ensuring RESET Valid to VCC = 0V on Active-High Push/Pull Outputs GND 100k Ω VCC VCC RESET MAX6316 MAX6318 MAX6319 Figure 8. Ensuring RESET Valid to VCC = 0V on Active-Low Push/Pull and Bidirectional Outputs |
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