You can create a rectangular-wave pulse generator with an exceptionally long period by employing just two elements: a National Semiconductor LM3710 supervisor IC and a 100-nF capacitor, which effectively eliminates noise spikes. This setup makes use of the watchdog feature and reset timers within the LM3710. The watchdog timer gets reset whenever a signal edge is detected on the WDI input (pin 4).
Continuous Grounding of WDI and Watchdog Operation
When WDI is consistently held at a ground level, the watchdog timer elapses without any edges. After a period TB, it initiates a reset pulse lasting for duration TA and is then reloaded with its initial value. This cycle repeats, producing pulses with a period of TA + TB at the RESET output (pin 10). This approach allows the generation of pulses spanning up to approximately 30 seconds, as indicated in the table. The intervals TA and TB are governed by internal timers within the IC. The LM3710 is available in different versions, each offering specific ranges for these timers. To achieve the desired period, the appropriate version of LM3710 must be selected.
Understanding LM3710 Version Selection
The type designation is decoded in the provided table. Notably, the reset threshold voltage is insignificant for this particular LM3710 application. The boldface versions listed were accessible at the time of printing; for the most recent information, manufacturers’ updates should be consulted on their official website (www.national.com). The numbers in brackets signify the minimum and maximum values for intervals TA and TB, respectively, within which the LM3710 is tested. The circuit functions within a supply voltage range of 3–5 V.
Versatility of LM3710/LM3711 Series
The LM3710/LM3711 series of microprocessor supervisory circuits offer unparalleled flexibility for monitoring power supplies and battery-operated functions in systems without backup batteries. This series is available in VSSOP-10 and 9-bump DSBGA packages, catering to diverse application needs and providing robust solutions for system supervision.
- Standard Reset Threshold Voltage: 3.08V
- Custom Reset Threshold Voltages: For other voltages between 2.2V and 5.0V in 10mV increments, contact TI
- No External Components Required
- Manual-Reset Input
- Precision Supply Voltage Monitor
- Separate Power Fail Comparator
- 28 µA VCC Supply Current