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Kernel driver ntc_thermistor

Documentation/hwmon/ntc_thermistor.rst

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Kernel driver ntc_thermistor

Supported thermistors from Murata:

  • Murata NTC Thermistors NCP15WB473, NCP18WB473, NCP21WB473, NCP03WB473, NCP15WL333, NCP03WF104, NCP15XH103

    Prefixes: 'ncp15wb473', 'ncp18wb473', 'ncp21wb473', 'ncp03wb473', 'ncp15wl333', 'ncp03wf104', 'ncp15xh103'

    Datasheet: Publicly available at Murata

Supported thermistors from EPCOS:

  • EPCOS NTC Thermistors B57330V2103

    Prefixes: b57330v2103

    Datasheet: Publicly available at EPCOS

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

Authors:

MyungJoo Ham <[email protected]>

Description

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.

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.

Using the following convention::

$ resistor [TH] the thermistor

The four circuit models provided are:

  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)

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

=============== == ============================================================= name the mandatory global attribute, the thermistor name. =============== == ============================================================= temp1_type RO always 4 (thermistor)

temp1_input RO measure the temperature and provide the measured value. (reading this file initiates the reading procedure.) =============== == =============================================================

Note that each NTC thermistor has only one thermistor; thus, only temp1 exists.