xref: /linux/Documentation/hwmon/ntc_thermistor.rst (revision c39f2d9db0fd81ea20bb5cce9b3f082ca63753e2)
1Kernel driver ntc_thermistor
2============================
3
4Supported thermistors from Murata:
5
6* Murata NTC Thermistors NCP15WB473, NCP18WB473, NCP21WB473, NCP03WB473,
7  NCP15WL333, NCP03WF104, NCP15XH103
8
9  Prefixes: 'ncp15wb473', 'ncp18wb473', 'ncp21wb473', 'ncp03wb473',
10  'ncp15wl333', 'ncp03wf104', 'ncp15xh103'
11
12  Datasheet: Publicly available at Murata
13
14Supported thermistors from EPCOS:
15
16* EPCOS NTC Thermistors B57330V2103
17
18  Prefixes: b57330v2103
19
20  Datasheet: Publicly available at EPCOS
21
22Other NTC thermistors can be supported simply by adding compensation
23tables; e.g., NCP15WL333 support is added by the table ncpXXwl333.
24
25Authors:
26
27	MyungJoo Ham <myungjoo.ham@samsung.com>
28
29Description
30-----------
31
32The NTC (Negative Temperature Coefficient) thermistor is a simple thermistor
33that requires users to provide the resistance and lookup the corresponding
34compensation table to get the temperature input.
35
36The NTC driver provides lookup tables with a linear approximation function
37and four circuit models with an option not to use any of the four models.
38
39Using the following convention::
40
41   $	resistor
42   [TH]	the thermistor
43
44The four circuit models provided are:
45
461. connect = NTC_CONNECTED_POSITIVE, pullup_ohm > 0::
47
48     [pullup_uV]
49	 |    |
50	[TH]  $ (pullup_ohm)
51	 |    |
52	 +----+-----------------------[read_uV]
53	 |
54	 $ (pulldown_ohm)
55	 |
56	-+- (ground)
57
582. connect = NTC_CONNECTED_POSITIVE, pullup_ohm = 0 (not-connected)::
59
60     [pullup_uV]
61	 |
62	[TH]
63	 |
64	 +----------------------------[read_uV]
65	 |
66	 $ (pulldown_ohm)
67	 |
68	-+- (ground)
69
703. connect = NTC_CONNECTED_GROUND, pulldown_ohm > 0::
71
72     [pullup_uV]
73	 |
74	 $ (pullup_ohm)
75	 |
76	 +----+-----------------------[read_uV]
77	 |    |
78	[TH]  $ (pulldown_ohm)
79	 |    |
80	-+----+- (ground)
81
824. connect = NTC_CONNECTED_GROUND, pulldown_ohm = 0 (not-connected)::
83
84     [pullup_uV]
85	 |
86	 $ (pullup_ohm)
87	 |
88	 +----------------------------[read_uV]
89	 |
90	[TH]
91	 |
92	-+- (ground)
93
94When one of the four circuit models is used, read_uV, pullup_uV, pullup_ohm,
95pulldown_ohm, and connect should be provided. When none of the four models
96are suitable or the user can get the resistance directly, the user should
97provide read_ohm and _not_ provide the others.
98
99Sysfs Interface
100---------------
101
102=============== == =============================================================
103name		   the mandatory global attribute, the thermistor name.
104=============== == =============================================================
105temp1_type	RO always 4 (thermistor)
106
107temp1_input	RO measure the temperature and provide the measured value.
108		   (reading this file initiates the reading procedure.)
109=============== == =============================================================
110
111Note that each NTC thermistor has only _one_ thermistor; thus, only temp1 exists.
112