1 # SPDX-License-Identifier: (GPL-2.0 OR BSD-2-C 1 # SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
2 --- 2 ---
3 $id: http://devicetree.org/schemas/hwmon/ntc-t 3 $id: http://devicetree.org/schemas/hwmon/ntc-thermistor.yaml#
4 $schema: http://devicetree.org/meta-schemas/co 4 $schema: http://devicetree.org/meta-schemas/core.yaml#
5 5
6 title: NTC thermistor temperature sensors 6 title: NTC thermistor temperature sensors
7 7
8 maintainers: 8 maintainers:
9 - Linus Walleij <linus.walleij@linaro.org> 9 - Linus Walleij <linus.walleij@linaro.org>
10 10
11 description: | 11 description: |
12 Thermistors with negative temperature coeffi 12 Thermistors with negative temperature coefficient (NTC) are resistors that
13 vary in resistance in an often non-linear wa 13 vary in resistance in an often non-linear way in relation to temperature.
14 The negative temperature coefficient means t 14 The negative temperature coefficient means that the resistance decreases
15 as the temperature rises. Since the relation 15 as the temperature rises. Since the relationship between resistance and
16 temperature is non-linear, software drivers 16 temperature is non-linear, software drivers most often need to use a look
17 up table and interpolation to get from resis 17 up table and interpolation to get from resistance to temperature.
18 18
19 When used in practice, a thermistor is often 19 When used in practice, a thermistor is often connected between ground, a
20 pull-up resistor or/and a pull-down resistor 20 pull-up resistor or/and a pull-down resistor and a fixed voltage like this:
21 21
22 + e.g. 5V = pull-up voltage (puv) 22 + e.g. 5V = pull-up voltage (puv)
23 | 23 |
24 +-+ 24 +-+
25 | | 25 | |
26 | | Pull-up resistor 26 | | Pull-up resistor
27 | | (puo) 27 | | (puo)
28 +-+ 28 +-+
29 |-------------------------o 29 |-------------------------o
30 +-+ | ^ 30 +-+ | ^
31 | |/ | 31 | |/ |
32 | / | 32 | / |
33 |/| Thermistor | Measured vol 33 |/| Thermistor | Measured voltage (mv)
34 / | | "connected g 34 / | | "connected ground"
35 /| | | 35 /| | |
36 +-+ | 36 +-+ |
37 |-------------------------o 37 |-------------------------o
38 +-+ ^ 38 +-+ ^
39 | | | 39 | | |
40 | | Pull-down resistor | Measured vol 40 | | Pull-down resistor | Measured voltage (mv)
41 | | (pdo) | "connected p 41 | | (pdo) | "connected positive"
42 +-+ | 42 +-+ |
43 | | 43 | |
44 | v 44 | v
45 + GND GND 45 + GND GND
46 46
47 The arrangements of where we measure the vol 47 The arrangements of where we measure the voltage over the thermistor are
48 called "connected ground" and "connected pos 48 called "connected ground" and "connected positive" and shall be understood as
49 the cases when either pull-up or pull-down r 49 the cases when either pull-up or pull-down resistance is zero.
50 50
51 If the pull-up resistance is 0 one end of th 51 If the pull-up resistance is 0 one end of the thermistor is connected to the
52 positive voltage and we get the thermistor o 52 positive voltage and we get the thermistor on top of a pull-down resistor
53 and we take the measure between the thermist 53 and we take the measure between the thermistor and the pull-down resistor.
54 54
55 Conversely if the pull-down resistance is ze 55 Conversely if the pull-down resistance is zero, one end of the thermistor is
56 connected to ground and we get the thermisto 56 connected to ground and we get the thermistor under the pull-up resistor
57 and we take the measure between the pull-up 57 and we take the measure between the pull-up resistor and the thermistor.
58 58
59 We can use both pull-up and pull-down resist 59 We can use both pull-up and pull-down resistors at the same time, and then
60 the figure illustrates where the voltage wil 60 the figure illustrates where the voltage will be measured for the "connected
61 ground" and "connected positive" cases. 61 ground" and "connected positive" cases.
62 62
63 properties: 63 properties:
64 $nodename: 64 $nodename:
65 pattern: "^thermistor(.*)?$" 65 pattern: "^thermistor(.*)?$"
66 66
67 compatible: 67 compatible:
68 oneOf: 68 oneOf:
69 - const: epcos,b57330v2103 69 - const: epcos,b57330v2103
70 - const: epcos,b57891s0103 70 - const: epcos,b57891s0103
71 - const: murata,ncp15wb473 71 - const: murata,ncp15wb473
72 - const: murata,ncp18wb473 72 - const: murata,ncp18wb473
73 - const: murata,ncp21wb473 73 - const: murata,ncp21wb473
74 - const: murata,ncp03wb473 74 - const: murata,ncp03wb473
75 - const: murata,ncp15wl333 75 - const: murata,ncp15wl333
76 - const: murata,ncp03wf104 76 - const: murata,ncp03wf104
77 - const: murata,ncp15xh103 77 - const: murata,ncp15xh103
78 - const: samsung,1404-001221 78 - const: samsung,1404-001221
79 # Deprecated "ntp," compatible strings 79 # Deprecated "ntp," compatible strings
80 - const: ntc,ncp15wb473 80 - const: ntc,ncp15wb473
81 deprecated: true 81 deprecated: true
82 - const: ntc,ncp18wb473 82 - const: ntc,ncp18wb473
83 deprecated: true 83 deprecated: true
84 - const: ntc,ncp21wb473 84 - const: ntc,ncp21wb473
85 deprecated: true 85 deprecated: true
86 - const: ntc,ncp03wb473 86 - const: ntc,ncp03wb473
87 deprecated: true 87 deprecated: true
88 - const: ntc,ncp15wl333 88 - const: ntc,ncp15wl333
89 deprecated: true 89 deprecated: true
90 90
91 "#thermal-sensor-cells": 91 "#thermal-sensor-cells":
92 description: Thermal sensor cells if used 92 description: Thermal sensor cells if used for thermal sensoring.
93 const: 0 93 const: 0
94 94
95 pullup-uv: 95 pullup-uv:
96 $ref: /schemas/types.yaml#/definitions/uin 96 $ref: /schemas/types.yaml#/definitions/uint32
97 description: Pull-up voltage in micro volt 97 description: Pull-up voltage in micro volts. Must always be specified.
98 98
99 pullup-ohm: 99 pullup-ohm:
100 $ref: /schemas/types.yaml#/definitions/uin 100 $ref: /schemas/types.yaml#/definitions/uint32
101 description: Pull-up resistance in ohms. M 101 description: Pull-up resistance in ohms. Must always be specified, even
102 if zero. 102 if zero.
103 103
104 pulldown-ohm: 104 pulldown-ohm:
105 $ref: /schemas/types.yaml#/definitions/uin 105 $ref: /schemas/types.yaml#/definitions/uint32
106 description: Pull-down resistance in ohms. 106 description: Pull-down resistance in ohms. Must always be specified, even
107 if zero. 107 if zero.
108 108
109 connected-positive: 109 connected-positive:
110 $ref: /schemas/types.yaml#/definitions/fla 110 $ref: /schemas/types.yaml#/definitions/flag
111 description: Indicates how the thermistor 111 description: Indicates how the thermistor is connected in series with
112 a pull-up and/or a pull-down resistor. S 112 a pull-up and/or a pull-down resistor. See the description above for
113 an illustration. If this flag is NOT spe 113 an illustration. If this flag is NOT specified, the thermistor is assumed
114 to be connected-ground, which usually me 114 to be connected-ground, which usually means a pull-down resistance of
115 zero but complex arrangements are possib 115 zero but complex arrangements are possible.
116 116
117 # See /schemas/iio/adc/adc.yaml 117 # See /schemas/iio/adc/adc.yaml
118 io-channels: 118 io-channels:
119 maxItems: 1 119 maxItems: 1
120 description: IIO ADC channel to read the v 120 description: IIO ADC channel to read the voltage over the resistor. Must
121 always be specified. 121 always be specified.
122 122
123 required: 123 required:
124 - compatible 124 - compatible
125 - pullup-uv 125 - pullup-uv
126 - pullup-ohm 126 - pullup-ohm
127 - pulldown-ohm 127 - pulldown-ohm
128 - io-channels 128 - io-channels
129 129
130 additionalProperties: false 130 additionalProperties: false
131 131
132 examples: 132 examples:
133 - | 133 - |
134 thermistor { 134 thermistor {
135 compatible = "murata,ncp18wb473"; 135 compatible = "murata,ncp18wb473";
136 io-channels = <&gpadc 0x06>; 136 io-channels = <&gpadc 0x06>;
137 pullup-uv = <1800000>; 137 pullup-uv = <1800000>;
138 pullup-ohm = <220000>; 138 pullup-ohm = <220000>;
139 pulldown-ohm = <0>; 139 pulldown-ohm = <0>;
140 #thermal-sensor-cells = <0>; 140 #thermal-sensor-cells = <0>;
141 }; 141 };
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