Documentation/devicetree/bindings/hwmon/ntc-thermistor.yaml

Source file repositories/reference/linux-study-clean/Documentation/devicetree/bindings/hwmon/ntc-thermistor.yaml

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Linux kernel
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Documentation/devicetree/bindings/hwmon/ntc-thermistor.yaml
Extension
.yaml
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4832 bytes
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143
Domain
Support Tooling And Documentation
Bucket
Documentation
Inferred role
Support Tooling And Documentation: configuration, schema, or hardware description
Status
atlas-only

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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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# 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:
  - Linus Walleij <linusw@kernel.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

Annotation

Implementation Notes