FreeBSD/Linux Kernel Cross Reference
sys/contrib/device-tree/Bindings/hwmon/ntc-thermistor.yaml

     # SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
     ---
     $id: http://devicetree.org/schemas/hwmon/ntc-thermistor.yaml#
     $schema: http://devicetree.org/meta-schemas/core.yaml#
     
     title: NTC thermistor temperature sensors
     
     maintainers:
       - Naveen Krishna Chatradhi <ch.naveen@samsung.com>
      - Linus Walleij <linus.walleij@linaro.org>
    
    description: |
      Thermistors with negative temperature coefficient (NTC) are resistors that
      vary in resistance in an often non-linear way in relation to temperature.
      The negative temperature coefficient means that the resistance decreases
      as the temperature rises. Since the relationship between resistance and
      temperature is non-linear, software drivers most often need to use a look
      up table and interpolation to get from resistance to temperature.
    
      When used in practice, a thermistor is often connected between ground, a
      pull-up resistor or/and a pull-down resistor and a fixed voltage like this:
    
          + e.g. 5V = pull-up voltage (puv)
          |
         +-+
         | |
         | | Pull-up resistor
         | | (puo)
         +-+
          |-------------------------o
         +-+ |                      ^
         | |/                       |
         | /                        |
         |/| Thermistor             | Measured voltage (mv)
         / |                        | "connected ground"
        /| |                        |
         +-+                        |
          |-------------------------o
         +-+                        ^
         | |                        |
         | | Pull-down resistor     | Measured voltage (mv)
         | | (pdo)                  | "connected positive"
         +-+                        |
          |                         |
          |                         v
          + GND                     GND
    
      The arrangements of where we measure the voltage over the thermistor are
      called "connected ground" and "connected positive" and shall be understood as
      the cases when either pull-up or pull-down resistance is zero.
    
      If the pull-up resistance is 0 one end of the thermistor is connected to the
      positive voltage and we get the thermistor on top of a pull-down resistor
      and we take the measure between the thermistor and the pull-down resistor.
    
      Conversely if the pull-down resistance is zero, one end of the thermistor is
      connected to ground and we get the thermistor under the pull-up resistor
      and we take the measure between the pull-up resistor and the thermistor.
    
      We can use both pull-up and pull-down resistors at the same time, and then
      the figure illustrates where the voltage will be measured for the "connected
      ground" and "connected positive" cases.
    
    properties:
      $nodename:
        pattern: "^thermistor(.*)?$"
    
      compatible:
        oneOf:
          - const: epcos,b57330v2103
          - const: epcos,b57891s0103
          - const: murata,ncp15wb473
          - const: murata,ncp18wb473
          - const: murata,ncp21wb473
          - const: murata,ncp03wb473
          - const: murata,ncp15wl333
          - const: murata,ncp03wf104
          - const: murata,ncp15xh103
          - const: samsung,1404-001221
          # Deprecated "ntp," compatible strings
          - const: ntc,ncp15wb473
            deprecated: true
          - const: ntc,ncp18wb473
            deprecated: true
          - const: ntc,ncp21wb473
            deprecated: true
          - const: ntc,ncp03wb473
            deprecated: true
          - const: ntc,ncp15wl333
            deprecated: true
    
      "#thermal-sensor-cells":
        description: Thermal sensor cells if used for thermal sensoring.
        const: 0
    
      pullup-uv:
        $ref: /schemas/types.yaml#/definitions/uint32
        description: Pull-up voltage in micro volts. Must always be specified.
    
     pullup-ohm:
       $ref: /schemas/types.yaml#/definitions/uint32
       description: Pull-up resistance in ohms. Must always be specified, even
         if zero.
   
     pulldown-ohm:
       $ref: /schemas/types.yaml#/definitions/uint32
       description: Pull-down resistance in ohms. Must always be specified, even
         if zero.
   
     connected-positive:
       $ref: /schemas/types.yaml#/definitions/flag
       description: Indicates how the thermistor is connected in series with
         a pull-up and/or a pull-down resistor. See the description above for
         an illustration. If this flag is NOT specified, the thermistor is assumed
         to be connected-ground, which usually means a pull-down resistance of
         zero but complex arrangements are possible.
   
     # See /schemas/iio/adc/adc.yaml
     io-channels:
       maxItems: 1
       description: IIO ADC channel to read the voltage over the resistor. Must
         always be specified.
   
   required:
     - compatible
     - pullup-uv
     - pullup-ohm
     - pulldown-ohm
     - io-channels
   
   additionalProperties: false
   
   examples:
     - |
       thermistor0 {
         compatible = "murata,ncp18wb473";
         io-channels = <&gpadc 0x06>;
         pullup-uv = <1800000>;
         pullup-ohm = <220000>;
         pulldown-ohm = <0>;
         #thermal-sensor-cells = <0>;
       };

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