0001 # SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
0002 ---
0003 $id: http://devicetree.org/schemas/hwmon/ntc-thermistor.yaml#
0004 $schema: http://devicetree.org/meta-schemas/core.yaml#
0005
0006 title: NTC thermistor temperature sensors
0007
0008 maintainers:
0009 - Naveen Krishna Chatradhi <ch.naveen@samsung.com>
0010 - Linus Walleij <linus.walleij@linaro.org>
0011
0012 description: |
0013 Thermistors with negative temperature coefficient (NTC) are resistors that
0014 vary in resistance in an often non-linear way in relation to temperature.
0015 The negative temperature coefficient means that the resistance decreases
0016 as the temperature rises. Since the relationship between resistance and
0017 temperature is non-linear, software drivers most often need to use a look
0018 up table and interpolation to get from resistance to temperature.
0019
0020 When used in practice, a thermistor is often connected between ground, a
0021 pull-up resistor or/and a pull-down resistor and a fixed voltage like this:
0022
0023 + e.g. 5V = pull-up voltage (puv)
0024 |
0025 +-+
0026 | |
0027 | | Pull-up resistor
0028 | | (puo)
0029 +-+
0030 |-------------------------o
0031 +-+ | ^
0032 | |/ |
0033 | / |
0034 |/| Thermistor | Measured voltage (mv)
0035 / | | "connected ground"
0036 /| | |
0037 +-+ |
0038 |-------------------------o
0039 +-+ ^
0040 | | |
0041 | | Pull-down resistor | Measured voltage (mv)
0042 | | (pdo) | "connected positive"
0043 +-+ |
0044 | |
0045 | v
0046 + GND GND
0047
0048 The arrangements of where we measure the voltage over the thermistor are
0049 called "connected ground" and "connected positive" and shall be understood as
0050 the cases when either pull-up or pull-down resistance is zero.
0051
0052 If the pull-up resistance is 0 one end of the thermistor is connected to the
0053 positive voltage and we get the thermistor on top of a pull-down resistor
0054 and we take the measure between the thermistor and the pull-down resistor.
0055
0056 Conversely if the pull-down resistance is zero, one end of the thermistor is
0057 connected to ground and we get the thermistor under the pull-up resistor
0058 and we take the measure between the pull-up resistor and the thermistor.
0059
0060 We can use both pull-up and pull-down resistors at the same time, and then
0061 the figure illustrates where the voltage will be measured for the "connected
0062 ground" and "connected positive" cases.
0063
0064 properties:
0065 $nodename:
0066 pattern: "^thermistor(.*)?$"
0067
0068 compatible:
0069 oneOf:
0070 - const: epcos,b57330v2103
0071 - const: epcos,b57891s0103
0072 - const: murata,ncp15wb473
0073 - const: murata,ncp18wb473
0074 - const: murata,ncp21wb473
0075 - const: murata,ncp03wb473
0076 - const: murata,ncp15wl333
0077 - const: murata,ncp03wf104
0078 - const: murata,ncp15xh103
0079 - const: samsung,1404-001221
0080 # Deprecated "ntp," compatible strings
0081 - const: ntc,ncp15wb473
0082 deprecated: true
0083 - const: ntc,ncp18wb473
0084 deprecated: true
0085 - const: ntc,ncp21wb473
0086 deprecated: true
0087 - const: ntc,ncp03wb473
0088 deprecated: true
0089 - const: ntc,ncp15wl333
0090 deprecated: true
0091
0092 "#thermal-sensor-cells":
0093 description: Thermal sensor cells if used for thermal sensoring.
0094 const: 0
0095
0096 pullup-uv:
0097 $ref: /schemas/types.yaml#/definitions/uint32
0098 description: Pull-up voltage in micro volts. Must always be specified.
0099
0100 pullup-ohm:
0101 $ref: /schemas/types.yaml#/definitions/uint32
0102 description: Pull-up resistance in ohms. Must always be specified, even
0103 if zero.
0104
0105 pulldown-ohm:
0106 $ref: /schemas/types.yaml#/definitions/uint32
0107 description: Pull-down resistance in ohms. Must always be specified, even
0108 if zero.
0109
0110 connected-positive:
0111 $ref: /schemas/types.yaml#/definitions/flag
0112 description: Indicates how the thermistor is connected in series with
0113 a pull-up and/or a pull-down resistor. See the description above for
0114 an illustration. If this flag is NOT specified, the thermistor is assumed
0115 to be connected-ground, which usually means a pull-down resistance of
0116 zero but complex arrangements are possible.
0117
0118 # See /schemas/iio/adc/adc.yaml
0119 io-channels:
0120 maxItems: 1
0121 description: IIO ADC channel to read the voltage over the resistor. Must
0122 always be specified.
0123
0124 required:
0125 - compatible
0126 - pullup-uv
0127 - pullup-ohm
0128 - pulldown-ohm
0129 - io-channels
0130
0131 additionalProperties: false
0132
0133 examples:
0134 - |
0135 thermistor0 {
0136 compatible = "murata,ncp18wb473";
0137 io-channels = <&gpadc 0x06>;
0138 pullup-uv = <1800000>;
0139 pullup-ohm = <220000>;
0140 pulldown-ohm = <0>;
0141 #thermal-sensor-cells = <0>;
0142 };
