1 # SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
4 $id: http://devicetree.org/schemas/iio/afe/temperature-transducer.yaml#
5 $schema: http://devicetree.org/meta-schemas/core.yaml#
7 title: Temperature Transducer
10 - Liam Beguin <liambeguin@gmail.com>
13 A temperature transducer is a device that converts a thermal quantity
14 into any other physical quantity. This binding applies to temperature to
15 voltage (like the LTC2997), and temperature to current (like the AD590)
17 In both cases these are assumed to be connected to a voltage ADC.
19 When an io-channel measures the output voltage of a temperature analog front
20 end such as a temperature transducer, the interesting measurement is almost
21 always the corresponding temperature, not the voltage output. This binding
22 describes such a circuit.
24 The general transfer function here is (using SI units)
25 V(T) = Rsense * Isense(T)
26 T = (Isense(T) / alpha) + offset
27 T = 1 / (Rsense * alpha) * (V + offset * Rsense * alpha)
29 When using a temperature to voltage transducer, Rsense is set to 1.
31 The following circuits show a temperature to current and a temperature to
32 voltage transducer that can be used with this binding.
41 V proportional to T +----+----+
43 +---- Vout | LTC2997 +--- Vout
45 +---+----+ +---------+
54 const: temperature-transducer
59 Channel node of a voltage io-channel.
64 sense-offset-millicelsius:
67 This offset is commonly used to convert from Kelvins to degrees Celsius.
68 In that case, sense-offset-millicelsius would be set to <(-273150)>.
74 By default sense-resistor-ohms cancels out the resistor making the
75 circuit behave like a temperature transducer.
78 alpha-ppm-per-celsius:
80 Sometimes referred to as output gain, slope, or temperature coefficient.
82 alpha is expressed in parts per million which can be micro-amps per
83 degrees Celsius or micro-volts per degrees Celsius. The is the main
84 characteristic of a temperature transducer and should be stated in the
87 additionalProperties: false
92 - alpha-ppm-per-celsius
96 ad950: temperature-sensor-0 {
97 compatible = "temperature-transducer";
98 #io-channel-cells = <0>;
99 io-channels = <&temp_adc 3>;
101 sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */
102 sense-resistor-ohms = <8060>;
103 alpha-ppm-per-celsius = <1>; /* 1 uA/K */
106 znq_tmp: temperature-sensor-1 {
107 compatible = "temperature-transducer";
108 #io-channel-cells = <0>;
109 io-channels = <&temp_adc 2>;
111 sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */
112 alpha-ppm-per-celsius = <4000>; /* 4 mV/K */