General
Review and verify the following for the custom schematic design:
- Above sections, including relevant application notes and FAQ links
- Pin attributes, signal description, and electrical specifications
- Electrical characteristics, timing parameters, and any additional available information
- The processor is required to restart (release reset) only after the voltages are below 0.3V after power-down (There is no time or range associated with the requirement. Each power rail is required to decay below 0.3V before any power rail is allowed to ramp back up)
- Reset input is asserted (low) while the processor supplies are ramping up or ramping down
- PORz (POR) input is 3.3V tolerant and fail-safe. The threshold follows the VDDS_OSC0 IO level
- IO level of warm reset RESETz (VDDSHV1) matches the IO supply for IO group supply (1.8V or 3.3V)
- Reset inputs follow the slew rate requirements (FS RESET, LVCMOS)
- Slew rate when open-drain output is connected (connecting through discrete push-pull output is recommended) directly to the reset input
- Follow reset requirements including slew rate and PORz hold time when a non-TI power architecture is used
Schematic Review
Follow the below list for the custom schematic design:
- Cold and warm reset inputs slew rate requirements are considered
- Cold reset input (PORz) deassertion hold time (PORz input delay after all the supplies ramp, 9.5ms minimum) after all supplies ramps are provided as per the data sheet requirement
- Provision for filter capacitor is provided at the input of the reset inputs (add 22pF (place holder) capacitor as a filter option and DNI)
- Connection of reset inputs when not used as per pin connectivity requirements
- Connection of push button warm reset inputs through debouncing circuit (Schmitt trigger buffer output based)
Additional
- PORz input has slew rate requirements specified. When connecting PMIC_POWERGOOD (open-drain output) to PORz is the only available option, adjust the pullup to optimize the rise time (< 200ns)
- PORz is a fail-safe input and 3.3V tolerant
- Connect the output from a discrete push-pull output buffer (fast rise time) as PORz input rather than slow rising open-drain output
- Not connecting a valid PORz causes unpredictable and random behavior, since processor does not get a valid reset input and the internal circuits are in random states. Slow ramp reset input causes internal processor reset circuit to glitch
- LVCMOS inputs have slew rate requirements specified. A schmitt trigger based debouncing circuit is recommended for the slow ramp push button RC connected to the processor warm reset inputs. Schmitt trigger based debouncing circuit is recommended when using a push button or an RC
- Provision for external ESD protection for manual reset input added near to the reset signal
- Fail-safe operation when connected to external reset inputs. Applying an external input before supply ramps causes voltage feed and affects the processor performance