ntc_thermistor.rst 2.74 KB
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Kernel driver ntc_thermistor
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============================
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Supported thermistors from Murata:
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* Murata NTC Thermistors NCP15WB473, NCP18WB473, NCP21WB473, NCP03WB473,
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  NCP15WL333, NCP03WF104, NCP15XH103
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  Prefixes: 'ncp15wb473', 'ncp18wb473', 'ncp21wb473', 'ncp03wb473',
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  'ncp15wl333', 'ncp03wf104', 'ncp15xh103'
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  Datasheet: Publicly available at Murata

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Supported thermistors from EPCOS:
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* EPCOS NTC Thermistors B57330V2103
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  Prefixes: b57330v2103
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  Datasheet: Publicly available at EPCOS

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Other NTC thermistors can be supported simply by adding compensation
tables; e.g., NCP15WL333 support is added by the table ncpXXwl333.

Authors:
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	MyungJoo Ham <myungjoo.ham@samsung.com>

Description
-----------

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The NTC (Negative Temperature Coefficient) thermistor is a simple thermistor
that requires users to provide the resistance and lookup the corresponding
compensation table to get the temperature input.
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The NTC driver provides lookup tables with a linear approximation function
and four circuit models with an option not to use any of the four models.

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Using the following convention::

   $	resistor
   [TH]	the thermistor

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The four circuit models provided are:

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1. connect = NTC_CONNECTED_POSITIVE, pullup_ohm > 0::

     [pullup_uV]
	 |    |
	[TH]  $ (pullup_ohm)
	 |    |
	 +----+-----------------------[read_uV]
	 |
	 $ (pulldown_ohm)
	 |
	-+- (ground)

2. connect = NTC_CONNECTED_POSITIVE, pullup_ohm = 0 (not-connected)::

     [pullup_uV]
	 |
	[TH]
	 |
	 +----------------------------[read_uV]
	 |
	 $ (pulldown_ohm)
	 |
	-+- (ground)

3. connect = NTC_CONNECTED_GROUND, pulldown_ohm > 0::

     [pullup_uV]
	 |
	 $ (pullup_ohm)
	 |
	 +----+-----------------------[read_uV]
	 |    |
	[TH]  $ (pulldown_ohm)
	 |    |
	-+----+- (ground)

4. connect = NTC_CONNECTED_GROUND, pulldown_ohm = 0 (not-connected)::

     [pullup_uV]
	 |
	 $ (pullup_ohm)
	 |
	 +----------------------------[read_uV]
	 |
	[TH]
	 |
	-+- (ground)
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When one of the four circuit models is used, read_uV, pullup_uV, pullup_ohm,
pulldown_ohm, and connect should be provided. When none of the four models
are suitable or the user can get the resistance directly, the user should
provide read_ohm and _not_ provide the others.

Sysfs Interface
---------------

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=============== == =============================================================
name		   the mandatory global attribute, the thermistor name.
=============== == =============================================================
temp1_type	RO always 4 (thermistor)
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temp1_input	RO measure the temperature and provide the measured value.
		   (reading this file initiates the reading procedure.)
=============== == =============================================================
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Note that each NTC thermistor has only _one_ thermistor; thus, only temp1 exists.