1-Wire - What are Parasitic Power design constraints
- You must check the maximum current output of the 1-Wire bus controller and the maximum combined instantaneous current consumption of all devices on it. When a DS18B20's capacitor is completely drained it will draw close to 1.5 mAs from the OneWire bus. If a 1-Wire controller can supply no more than 15the voltage will become unstable if more than 10 DS18B20 devices charge at the same time. There can be more than 10 DS18B20 devices on the bus, but they can not all charge at the same time.
- Circuits like this one can be used to increase the available current on a 1-Wire bus.
- The capacitor of a 1-wire device holds a limited charge (typically 800pf). Devices need to rest between operations to recharge it. High frequency polling of one-wire sensors is not possible. Device dartasheets will indicate the required rest periods.