The DS18B20-PAR, DS18S20-PAR, and DS1822-PAR parasite-power 1-Wire digital temperature sensors are ideal for use in remote temperature-sensing applications where space constraints or lack of accessibility make it impractical to use a local power supply. "Parasite power" is a feature of most 1-Wire devices, which allows them to derive power directly from the data line. The -PAR temperature sensor ICs can greatly simplify the mechanical aspects of implementing parasite power in remote applications, as compared to the DS18B20, DS18S20, and DS1822.
The "-PAR" Advantage
When using the DS18B20, DS18S20, and DS1822 1-Wire temperature sensors in parasite-power mode, the VDD
pin must be connected to ground (GND) for correct operation. In applications where the sensors are attached directly to a printed circuit board, connecting the VDD
pin to GND is a simple matter. However, in applications where the temperature sensor is located at a remote location from the control circuit (e.g., in a temperature probe), this connection can present some mechanical difficulties. In this case there are two ways to make the required connection: run three wires to the temperature sensor and connect the VDD
wire to GND at the circuit board (see Figure 1
), or connect the VDD
pin to the GND pin at the device (see Figure 2
). Unfortunately, the first approach adds expense by requiring a wire for the VDD
connection, which is of particular concern if the wires must span long distances, and the second approach is a mechanically awkward solution.
Figure 1. 1-Wire temperature sensor with VDD pin connected to GND at PCB.
Figure 2. 1-Wire temperature sensor with VDD pin locally connected to GND.
To solve this problem, Dallas created the DS18B20-PAR, DS18S20-PAR, and DS1822-PAR. These devices are identical to the DS18B20, DS18S20, and DS1822 except that VDD
is internally connected to GND (see Figure 3
). Therefore, the three -PAR devices make it simple to implement remote parasite-power operation with minimal wiring or connections (see Figure 4
Figure 3. Cutaway view of -PAR temperature sensor.
Figure 4. -PAR wiring configuration.
Note that due to increased DQ pin leakage current at high temperatures, the DS18B20-PAR, DS18S20-PAR, and DS1822-PAR have a maximum operational temperature of +100°C. The same is true for the DS18B20, DS18S20, and DS1822 when operated in parasite-power mode.
If you require further information about the DS18B20-PAR, DS18S20-PAR, or DS1822-PAR, or any other Dallas temperature sensor, please contact our technical support staff
. DS18B20-PAR, DS18S20-PAR, or DS1822-PAR data sheets can be downloaded from the Maxim website at www.maximintegrated.com