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Diffstat (limited to 'Documentation/devicetree/bindings/hwmon/ntc-thermistor.yaml')
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diff --git a/Documentation/devicetree/bindings/hwmon/ntc-thermistor.yaml b/Documentation/devicetree/bindings/hwmon/ntc-thermistor.yaml new file mode 100644 index 000000000..3d3b139a9 --- /dev/null +++ b/Documentation/devicetree/bindings/hwmon/ntc-thermistor.yaml @@ -0,0 +1,142 @@ +# 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>; + }; |