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 - Naveen Krishna Chatradhi <ch.naveen@samsung.com>
9 - Linus Walleij <linus.walleij@linaro.org> 10 - Linus Walleij <linus.walleij@linaro.org>
10 11
11 description: | 12 description: |
12 Thermistors with negative temperature coeffi 13 Thermistors with negative temperature coefficient (NTC) are resistors that
13 vary in resistance in an often non-linear wa 14 vary in resistance in an often non-linear way in relation to temperature.
14 The negative temperature coefficient means t 15 The negative temperature coefficient means that the resistance decreases
15 as the temperature rises. Since the relation 16 as the temperature rises. Since the relationship between resistance and
16 temperature is non-linear, software drivers 17 temperature is non-linear, software drivers most often need to use a look
17 up table and interpolation to get from resis 18 up table and interpolation to get from resistance to temperature.
18 19
19 When used in practice, a thermistor is often 20 When used in practice, a thermistor is often connected between ground, a
20 pull-up resistor or/and a pull-down resistor 21 pull-up resistor or/and a pull-down resistor and a fixed voltage like this:
21 22
22 + e.g. 5V = pull-up voltage (puv) 23 + e.g. 5V = pull-up voltage (puv)
23 | 24 |
24 +-+ 25 +-+
25 | | 26 | |
26 | | Pull-up resistor 27 | | Pull-up resistor
27 | | (puo) 28 | | (puo)
28 +-+ 29 +-+
29 |-------------------------o 30 |-------------------------o
30 +-+ | ^ 31 +-+ | ^
31 | |/ | 32 | |/ |
32 | / | 33 | / |
33 |/| Thermistor | Measured vol 34 |/| Thermistor | Measured voltage (mv)
34 / | | "connected g 35 / | | "connected ground"
35 /| | | 36 /| | |
36 +-+ | 37 +-+ |
37 |-------------------------o 38 |-------------------------o
38 +-+ ^ 39 +-+ ^
39 | | | 40 | | |
40 | | Pull-down resistor | Measured vol 41 | | Pull-down resistor | Measured voltage (mv)
41 | | (pdo) | "connected p 42 | | (pdo) | "connected positive"
42 +-+ | 43 +-+ |
43 | | 44 | |
44 | v 45 | v
45 + GND GND 46 + GND GND
46 47
47 The arrangements of where we measure the vol 48 The arrangements of where we measure the voltage over the thermistor are
48 called "connected ground" and "connected pos 49 called "connected ground" and "connected positive" and shall be understood as
49 the cases when either pull-up or pull-down r 50 the cases when either pull-up or pull-down resistance is zero.
50 51
51 If the pull-up resistance is 0 one end of th 52 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 53 positive voltage and we get the thermistor on top of a pull-down resistor
53 and we take the measure between the thermist 54 and we take the measure between the thermistor and the pull-down resistor.
54 55
55 Conversely if the pull-down resistance is ze 56 Conversely if the pull-down resistance is zero, one end of the thermistor is
56 connected to ground and we get the thermisto 57 connected to ground and we get the thermistor under the pull-up resistor
57 and we take the measure between the pull-up 58 and we take the measure between the pull-up resistor and the thermistor.
58 59
59 We can use both pull-up and pull-down resist 60 We can use both pull-up and pull-down resistors at the same time, and then
60 the figure illustrates where the voltage wil 61 the figure illustrates where the voltage will be measured for the "connected
61 ground" and "connected positive" cases. 62 ground" and "connected positive" cases.
62 63
63 properties: 64 properties:
64 $nodename: 65 $nodename:
65 pattern: "^thermistor(.*)?$" 66 pattern: "^thermistor(.*)?$"
66 67
67 compatible: 68 compatible:
68 oneOf: 69 oneOf:
69 - const: epcos,b57330v2103 70 - const: epcos,b57330v2103
70 - const: epcos,b57891s0103 71 - const: epcos,b57891s0103
71 - const: murata,ncp15wb473 72 - const: murata,ncp15wb473
72 - const: murata,ncp18wb473 73 - const: murata,ncp18wb473
73 - const: murata,ncp21wb473 74 - const: murata,ncp21wb473
74 - const: murata,ncp03wb473 75 - const: murata,ncp03wb473
75 - const: murata,ncp15wl333 76 - const: murata,ncp15wl333
76 - const: murata,ncp03wf104 77 - const: murata,ncp03wf104
77 - const: murata,ncp15xh103 78 - const: murata,ncp15xh103
78 - const: samsung,1404-001221 79 - const: samsung,1404-001221
79 # Deprecated "ntp," compatible strings 80 # Deprecated "ntp," compatible strings
80 - const: ntc,ncp15wb473 81 - const: ntc,ncp15wb473
81 deprecated: true 82 deprecated: true
82 - const: ntc,ncp18wb473 83 - const: ntc,ncp18wb473
83 deprecated: true 84 deprecated: true
84 - const: ntc,ncp21wb473 85 - const: ntc,ncp21wb473
85 deprecated: true 86 deprecated: true
86 - const: ntc,ncp03wb473 87 - const: ntc,ncp03wb473
87 deprecated: true 88 deprecated: true
88 - const: ntc,ncp15wl333 89 - const: ntc,ncp15wl333
89 deprecated: true 90 deprecated: true
90 91
91 "#thermal-sensor-cells": 92 "#thermal-sensor-cells":
92 description: Thermal sensor cells if used 93 description: Thermal sensor cells if used for thermal sensoring.
93 const: 0 94 const: 0
94 95
95 pullup-uv: 96 pullup-uv:
96 $ref: /schemas/types.yaml#/definitions/uin 97 $ref: /schemas/types.yaml#/definitions/uint32
97 description: Pull-up voltage in micro volt 98 description: Pull-up voltage in micro volts. Must always be specified.
98 99
99 pullup-ohm: 100 pullup-ohm:
100 $ref: /schemas/types.yaml#/definitions/uin 101 $ref: /schemas/types.yaml#/definitions/uint32
101 description: Pull-up resistance in ohms. M 102 description: Pull-up resistance in ohms. Must always be specified, even
102 if zero. 103 if zero.
103 104
104 pulldown-ohm: 105 pulldown-ohm:
105 $ref: /schemas/types.yaml#/definitions/uin 106 $ref: /schemas/types.yaml#/definitions/uint32
106 description: Pull-down resistance in ohms. 107 description: Pull-down resistance in ohms. Must always be specified, even
107 if zero. 108 if zero.
108 109
109 connected-positive: 110 connected-positive:
110 $ref: /schemas/types.yaml#/definitions/fla 111 $ref: /schemas/types.yaml#/definitions/flag
111 description: Indicates how the thermistor 112 description: Indicates how the thermistor is connected in series with
112 a pull-up and/or a pull-down resistor. S 113 a pull-up and/or a pull-down resistor. See the description above for
113 an illustration. If this flag is NOT spe 114 an illustration. If this flag is NOT specified, the thermistor is assumed
114 to be connected-ground, which usually me 115 to be connected-ground, which usually means a pull-down resistance of
115 zero but complex arrangements are possib 116 zero but complex arrangements are possible.
116 117
117 # See /schemas/iio/adc/adc.yaml 118 # See /schemas/iio/adc/adc.yaml
118 io-channels: 119 io-channels:
119 maxItems: 1 120 maxItems: 1
120 description: IIO ADC channel to read the v 121 description: IIO ADC channel to read the voltage over the resistor. Must
121 always be specified. 122 always be specified.
122 123
123 required: 124 required:
124 - compatible 125 - compatible
125 - pullup-uv 126 - pullup-uv
126 - pullup-ohm 127 - pullup-ohm
127 - pulldown-ohm 128 - pulldown-ohm
128 - io-channels 129 - io-channels
129 130
130 additionalProperties: false 131 additionalProperties: false
131 132
132 examples: 133 examples:
133 - | 134 - |
134 thermistor { !! 135 thermistor0 {
135 compatible = "murata,ncp18wb473"; 136 compatible = "murata,ncp18wb473";
136 io-channels = <&gpadc 0x06>; 137 io-channels = <&gpadc 0x06>;
137 pullup-uv = <1800000>; 138 pullup-uv = <1800000>;
138 pullup-ohm = <220000>; 139 pullup-ohm = <220000>;
139 pulldown-ohm = <0>; 140 pulldown-ohm = <0>;
140 #thermal-sensor-cells = <0>; 141 #thermal-sensor-cells = <0>;
141 }; 142 };
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