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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 <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:
+ - |
+ thermistor {
+ compatible = "murata,ncp18wb473";
+ io-channels = <&gpadc 0x06>;
+ pullup-uv = <1800000>;
+ pullup-ohm = <220000>;
+ pulldown-ohm = <0>;
+ #thermal-sensor-cells = <0>;
+ };