142 lines
4.7 KiB
YAML
142 lines
4.7 KiB
YAML
# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
|
|
---
|
|
$id: http://devicetree.org/schemas/hwmon/ntc-thermistor.yaml#
|
|
$schema: http://devicetree.org/meta-schemas/core.yaml#
|
|
|
|
title: NTC thermistor temperature sensors
|
|
|
|
maintainers:
|
|
- Linus Walleij <linus.walleij@linaro.org>
|
|
|
|
description: |
|
|
Thermistors with negative temperature coefficient (NTC) are resistors that
|
|
vary in resistance in an often non-linear way in relation to temperature.
|
|
The negative temperature coefficient means that the resistance decreases
|
|
as the temperature rises. Since the relationship between resistance and
|
|
temperature is non-linear, software drivers most often need to use a look
|
|
up table and interpolation to get from resistance to temperature.
|
|
|
|
When used in practice, a thermistor is often connected between ground, a
|
|
pull-up resistor or/and a pull-down resistor and a fixed voltage like this:
|
|
|
|
+ e.g. 5V = pull-up voltage (puv)
|
|
|
|
|
+-+
|
|
| |
|
|
| | Pull-up resistor
|
|
| | (puo)
|
|
+-+
|
|
|-------------------------o
|
|
+-+ | ^
|
|
| |/ |
|
|
| / |
|
|
|/| Thermistor | Measured voltage (mv)
|
|
/ | | "connected ground"
|
|
/| | |
|
|
+-+ |
|
|
|-------------------------o
|
|
+-+ ^
|
|
| | |
|
|
| | Pull-down resistor | Measured voltage (mv)
|
|
| | (pdo) | "connected positive"
|
|
+-+ |
|
|
| |
|
|
| v
|
|
+ GND GND
|
|
|
|
The arrangements of where we measure the voltage over the thermistor are
|
|
called "connected ground" and "connected positive" and shall be understood as
|
|
the cases when either pull-up or pull-down resistance is zero.
|
|
|
|
If the pull-up resistance is 0 one end of the thermistor is connected to the
|
|
positive voltage and we get the thermistor on top of a pull-down resistor
|
|
and we take the measure between the thermistor and the pull-down resistor.
|
|
|
|
Conversely if the pull-down resistance is zero, one end of the thermistor is
|
|
connected to ground and we get the thermistor under the pull-up resistor
|
|
and we take the measure between the pull-up resistor and the thermistor.
|
|
|
|
We can use both pull-up and pull-down resistors at the same time, and then
|
|
the figure illustrates where the voltage will be measured for the "connected
|
|
ground" and "connected positive" cases.
|
|
|
|
properties:
|
|
$nodename:
|
|
pattern: "^thermistor(.*)?$"
|
|
|
|
compatible:
|
|
oneOf:
|
|
- const: epcos,b57330v2103
|
|
- const: epcos,b57891s0103
|
|
- const: murata,ncp15wb473
|
|
- const: murata,ncp18wb473
|
|
- const: murata,ncp21wb473
|
|
- const: murata,ncp03wb473
|
|
- const: murata,ncp15wl333
|
|
- const: murata,ncp03wf104
|
|
- const: murata,ncp15xh103
|
|
- const: samsung,1404-001221
|
|
# Deprecated "ntp," compatible strings
|
|
- const: ntc,ncp15wb473
|
|
deprecated: true
|
|
- const: ntc,ncp18wb473
|
|
deprecated: true
|
|
- const: ntc,ncp21wb473
|
|
deprecated: true
|
|
- const: ntc,ncp03wb473
|
|
deprecated: true
|
|
- const: ntc,ncp15wl333
|
|
deprecated: true
|
|
|
|
"#thermal-sensor-cells":
|
|
description: Thermal sensor cells if used for thermal sensoring.
|
|
const: 0
|
|
|
|
pullup-uv:
|
|
$ref: /schemas/types.yaml#/definitions/uint32
|
|
description: Pull-up voltage in micro volts. Must always be specified.
|
|
|
|
pullup-ohm:
|
|
$ref: /schemas/types.yaml#/definitions/uint32
|
|
description: Pull-up resistance in ohms. Must always be specified, even
|
|
if zero.
|
|
|
|
pulldown-ohm:
|
|
$ref: /schemas/types.yaml#/definitions/uint32
|
|
description: Pull-down resistance in ohms. Must always be specified, even
|
|
if zero.
|
|
|
|
connected-positive:
|
|
$ref: /schemas/types.yaml#/definitions/flag
|
|
description: Indicates how the thermistor is connected in series with
|
|
a pull-up and/or a pull-down resistor. See the description above for
|
|
an illustration. If this flag is NOT specified, the thermistor is assumed
|
|
to be connected-ground, which usually means a pull-down resistance of
|
|
zero but complex arrangements are possible.
|
|
|
|
# See /schemas/iio/adc/adc.yaml
|
|
io-channels:
|
|
maxItems: 1
|
|
description: IIO ADC channel to read the voltage over the resistor. Must
|
|
always be specified.
|
|
|
|
required:
|
|
- compatible
|
|
- pullup-uv
|
|
- pullup-ohm
|
|
- pulldown-ohm
|
|
- io-channels
|
|
|
|
additionalProperties: false
|
|
|
|
examples:
|
|
- |
|
|
thermistor {
|
|
compatible = "murata,ncp18wb473";
|
|
io-channels = <&gpadc 0x06>;
|
|
pullup-uv = <1800000>;
|
|
pullup-ohm = <220000>;
|
|
pulldown-ohm = <0>;
|
|
#thermal-sensor-cells = <0>;
|
|
};
|