Book a Demo!
CoCalc Logo Icon
StoreFeaturesDocsShareSupportNewsAboutPoliciesSign UpSign In
torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml
26309 views
1
# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)

2
%YAML 1.2

3
---

4
$id: http://devicetree.org/schemas/iio/afe/temperature-transducer.yaml#

5
$schema: http://devicetree.org/meta-schemas/core.yaml#

6


7
title: Temperature Transducer

8


9
maintainers:

10
  - Liam Beguin <liambeguin@gmail.com>

11


12
description: |

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)

16
  linear transducers.

17
  In both cases these are assumed to be connected to a voltage ADC.

18


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.

23


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)

28


29
  When using a temperature to voltage transducer, Rsense is set to 1.

30


31
  The following circuits show a temperature to current and a temperature to

32
  voltage transducer that can be used with this binding.

33


34
           VCC

35
          -----

36
            |

37
        +---+---+

38
        | AD590 |                               VCC

39
        +---+---+                              -----

40
            |                                    |

41
            V proportional to T             +----+----+

42
            |                          D+ --+         |

43
            +---- Vout                      | LTC2997 +--- Vout

44
            |                          D- --+         |

45
        +---+----+                          +---------+

46
        | Rsense |                               |

47
        +---+----+                             -----

48
            |                                   GND

49
          -----

50
           GND

51


52
properties:

53
  compatible:

54
    const: temperature-transducer

55


56
  io-channels:

57
    maxItems: 1

58
    description: |

59
      Channel node of a voltage io-channel.

60


61
  '#io-channel-cells':

62
    const: 0

63


64
  sense-offset-millicelsius:

65
    description: |

66
      Temperature offset.

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)>.

69
    default: 0

70


71
  sense-resistor-ohms:

72
    description: |

73
      The sense resistor.

74
      By default sense-resistor-ohms cancels out the resistor making the

75
      circuit behave like a temperature transducer.

76
    default: 1

77


78
  alpha-ppm-per-celsius:

79
    description: |

80
      Sometimes referred to as output gain, slope, or temperature coefficient.

81


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

85
      datasheet.

86


87
additionalProperties: false

88


89
required:

90
  - compatible

91
  - io-channels

92
  - alpha-ppm-per-celsius

93


94
examples:

95
  - |

96
    ad950: temperature-sensor-0 {

97
        compatible = "temperature-transducer";

98
        #io-channel-cells = <0>;

99
        io-channels = <&temp_adc 3>;

100


101
        sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */

102
        sense-resistor-ohms = <8060>;

103
        alpha-ppm-per-celsius = <1>; /* 1 uA/K */

104
    };

105
  - |

106
    znq_tmp: temperature-sensor-1 {

107
        compatible = "temperature-transducer";

108
        #io-channel-cells = <0>;

109
        io-channels = <&temp_adc 2>;

110


111
        sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */

112
        alpha-ppm-per-celsius = <4000>; /* 4 mV/K */

113
    };

114
...

115


116