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