1 # SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
3 $id: http://devicetree.org/schemas/hwmon/ntc-thermistor.yaml#
4 $schema: http://devicetree.org/meta-schemas/core.yaml#
6 title: NTC thermistor temperature sensors
9 - Naveen Krishna Chatradhi <ch.naveen@samsung.com>
10 - Linus Walleij <linus.walleij@linaro.org>
13 Thermistors with negative temperature coefficient (NTC) are resistors that
14 vary in resistance in an often non-linear way in relation to temperature.
15 The negative temperature coefficient means that the resistance decreases
16 as the temperature rises. Since the relationship between resistance and
17 temperature is non-linear, software drivers most often need to use a look
18 up table and interpolation to get from resistance to temperature.
20 When used in practice, a thermistor is often connected between ground, a
21 pull-up resistor or/and a pull-down resistor and a fixed voltage like this:
23 + e.g. 5V = pull-up voltage (puv)
30 |-------------------------o
34 |/| Thermistor | Measured voltage (mv)
35 / | | "connected ground"
38 |-------------------------o
41 | | Pull-down resistor | Measured voltage (mv)
42 | | (pdo) | "connected positive"
48 The arrangements of where we measure the voltage over the thermistor are
49 called "connected ground" and "connected positive" and shall be understood as
50 the cases when either pull-up or pull-down resistance is zero.
52 If the pull-up resistance is 0 one end of the thermistor is connected to the
53 positive voltage and we get the thermistor on top of a pull-down resistor
54 and we take the measure between the thermistor and the pull-down resistor.
56 Conversely if the pull-down resistance is zero, one end of the thermistor is
57 connected to ground and we get the thermistor under the pull-up resistor
58 and we take the measure between the pull-up resistor and the thermistor.
60 We can use both pull-up and pull-down resistors at the same time, and then
61 the figure illustrates where the voltage will be measured for the "connected
62 ground" and "connected positive" cases.
66 pattern: "^thermistor(.*)?$"
70 - const: epcos,b57330v2103
71 - const: epcos,b57891s0103
72 - const: murata,ncp15wb473
73 - const: murata,ncp18wb473
74 - const: murata,ncp21wb473
75 - const: murata,ncp03wb473
76 - const: murata,ncp15wl333
77 - const: murata,ncp03wf104
78 - const: murata,ncp15xh103
79 - const: samsung,1404-001221
80 # Deprecated "ntp," compatible strings
81 - const: ntc,ncp15wb473
83 - const: ntc,ncp18wb473
85 - const: ntc,ncp21wb473
87 - const: ntc,ncp03wb473
89 - const: ntc,ncp15wl333
92 "#thermal-sensor-cells":
93 description: Thermal sensor cells if used for thermal sensoring.
97 $ref: /schemas/types.yaml#/definitions/uint32
98 description: Pull-up voltage in micro volts. Must always be specified.
101 $ref: /schemas/types.yaml#/definitions/uint32
102 description: Pull-up resistance in ohms. Must always be specified, even
106 $ref: /schemas/types.yaml#/definitions/uint32
107 description: Pull-down resistance in ohms. Must always be specified, even
111 $ref: /schemas/types.yaml#/definitions/flag
112 description: Indicates how the thermistor is connected in series with
113 a pull-up and/or a pull-down resistor. See the description above for
114 an illustration. If this flag is NOT specified, the thermistor is assumed
115 to be connected-ground, which usually means a pull-down resistance of
116 zero but complex arrangements are possible.
118 # See /schemas/iio/adc/adc.yaml
121 description: IIO ADC channel to read the voltage over the resistor. Must
131 additionalProperties: false
136 compatible = "murata,ncp18wb473";
137 io-channels = <&gpadc 0x06>;
138 pullup-uv = <1800000>;
139 pullup-ohm = <220000>;
141 #thermal-sensor-cells = <0>;