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STWD100NYWY3E Datasheet(PDF) 7 Page - STMicroelectronics |
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STWD100NYWY3E Datasheet(HTML) 7 Page - STMicroelectronics |
7 / 25 page STWD100 Operation 7/25 2 Operation The STWD100 device is used to detect an out-of-control MCU. The user has to ensure watchdog reset within the watchdog timeout period, otherwise the watchdog output is asserted and MCU is restarted. The STWD100 can be also enabled or disabled by the chip- enable pin. 2.1 Watchdog input (WDI) The WDI input has to be toggled within the watchdog timeout period, tWD, otherwise the watchdog output, WDO, is asserted. The internal watchdog timer, which counts the tWD period, is cleared either: 1. by a transition on watchdog output, WDO (see Figure 8) or 2. by a pulse on enable pin, EN (see Figure 10) or 3. by toggling WDI input (low-to-high on all versions and high-to-low on STWD100xW, STWD100xX and STWD100xY only). The pulses on WDI input with a duration of at least 1 µs are detected and glitches shorter than 100 ns are ignored. If WDI is permanently tied high or low and EN is tied low, the WDO toggles every 3.4 ms (tWD) on STWD100xP and every tWD and tPW on STWD100xW, STWD100xX and STWD100xY (see Figure 8). 2.2 Watchdog output (WDO) When the VCC exceeds the timer startup voltage VSTART after power-up, the internal watchdog timer starts counting. If the timer is not cleared within the tWD, the WDO will go low (see Figure 6). After exceeding the tWD, the WDO is asserted for tPW on STWD100xW, STWD100xX and STWD100xY regardless of possible WDI transitions (see Figure 9). On STWD100xP WDO is asserted for a minimum of 10 µs and a maximum of tWD after exceeding the tWD period (see Figure 8 and Figure 9). The STWD100 has an active-low open drain or push-pull output. An external pull-up resistor connected to any supply voltage up to 6 V is required in case of open drain WDO output (see Figure 4). Select a resistor value large enough to register a logic low, and small enough to register a logic high while supplying all input current and leakage paths connected to the reset output line. A 10 k Ω pull-up resistor is sufficient in most applications. |
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