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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: - Naveen Krishna Chatradhi - Linus Walleij 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 # 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>; };