What role does the DS18B20 digital temperature sensor play in a circuit?
Release Date:
2021-11-30
Author:
DS18B20 digital temperature sensor It offers advantages such as a simple temperature‑measurement system, high measurement accuracy, convenient connectivity, and minimal pin count. It derives power from the single‑wire data line: during the DQ line’s high‑level period, it stores energy in an internal capacitor; during the low‑level period, it draws on the stored energy to charge the parasitic capacitance until the next high‑level transition.
The unique parasitic power method has three advantages:
1. Remote temperature measurement does not require a local power supply.
2. Read-only memory can be read without a conventional power supply.
3. The circuit is simpler, using only a single I/O port to measure temperature.
To ensure accurate temperature conversion by digital temperature sensors, the I/O line must supply sufficient power during the conversion process. Since each DS18B20 draws up to 1 mA during temperature conversion, when multiple temperature sensors are connected to the same I/O line for multipoint temperature measurement, a 4.7 kΩ pull-up resistor cannot provide enough current, resulting in failed conversions or significant temperature errors.
Therefore, the circuit is suitable only for temperature measurement with a single temperature sensor and is not appropriate for battery-powered systems. The supply voltage VCC must be maintained at 5 V. As the supply voltage decreases, the energy that the parasitic power can absorb also diminishes, leading to increased temperature errors.
To ensure that the digital temperature sensor receives sufficient current during dynamic conversion cycles, a MOSFET can be used to directly pull the I/O line up to VCC when performing temperature conversion or writing data to the E2 memory, thereby providing adequate current. After issuing any command related to writing to the E2 memory or initiating temperature conversion, the input/output line must remain in a strong‑pull‑up state for an additional 10 µs. In this strong‑pull‑up mode, the issue of residual supply current is mitigated, making it well suited for multi‑point temperature‑measurement applications. The drawback is that implementing strong pull‑up requires an extra I/O port line.
In external power mode, DS18B20 digital temperature sensor The device’s operating power is supplied via the VDD pin. Under these conditions, there is no need to forcibly pull the I/O lines, and there is no risk of insufficient supply current, ensuring conversion accuracy. Furthermore, in theory, any number of DS18B20 digital temperature sensors can be connected to the bus, forming a multi-point temperature‑measurement system. In external‑power mode, the DS18B20’s GND pin must not be left floating; otherwise, the temperature cannot be adjusted, and the reported temperature will remain fixed at 85°C.
DS18B20 digital temperature sensor It operates stably and reliably, with strong anti-interference capabilities and a simple circuit design, making it suitable for developing a stable and dependable multi-point temperature monitoring system. We recommend using an external power supply during development. After all, this configuration provides one additional VCC lead compared to the parasitic‑power mode. With an external power supply, you can fully leverage the DS18B20 digital temperature sensor’s wide supply‑voltage range; even when the VCC drops to 3 V, temperature measurement accuracy remains assured.
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