On Tue, Jul 06, 2021 at 12:09:42PM -0400, Liam Beguin wrote: > From: Liam Beguin <lvb@xxxxxxxxxx> > > An ADC is often used to measure other quantities indirectly. > This binding describe one case, the measurement of a temperature > through a temperature transducer (either voltage or current). > > Signed-off-by: Liam Beguin <lvb@xxxxxxxxxx> > --- > .../iio/afe/temperature-transducer.yaml | 111 ++++++++++++++++++ > 1 file changed, 111 insertions(+) > create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml > > diff --git a/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml b/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml > new file mode 100644 > index 000000000000..b5a4fbfe75e4 > --- /dev/null > +++ b/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml > @@ -0,0 +1,111 @@ > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) > +%YAML 1.2 > +--- > +$id: http://devicetree.org/schemas/iio/afe/temperature-transducer.yaml# > +$schema: http://devicetree.org/meta-schemas/core.yaml# > + > +title: Temperature Transducer > + > +maintainers: > + - Liam Beguin <lvb@xxxxxxxxxx> > + > +description: | > + A temperature transducer is a device that converts a thermal quantity > + into any other physical quantity. This binding applies to temperature to > + voltage (like the LTC2997), and temperature to current (like the AD590) > + linear transducers. > + In both cases these are assumed to be connected to a voltage ADC. > + > + When an io-channel measures the output voltage of a temperature analog front > + end such as a temperature transducer, the interesting measurement is almost > + always the corresponding temperature, not the voltage output. This binding > + describes such a circuit. > + > + The general transfer function here is (using SI units) > + V(T) = Rsense * Isense(T) > + T = (Isense(T) / alpha) + offset > + T = 1 / (Rsense * alpha) * (V + offset * Rsense * alpha) > + > + When using a temperature to voltage transducer, Rsense is set to 1. > + > + The following circuits show a temperature to current and a temperature to > + voltage transducer that can be used with this binding. > + > + VCC > + ----- > + | > + +---+---+ > + | AD590 | VCC > + +---+---+ ----- > + | | > + V proportional to T +----+----+ > + | D+ --+ | > + +---- Vout | LTC2997 +--- Vout > + | D- --+ | > + +---+----+ +---------+ > + | Rsense | | > + +---+----+ ----- > + | GND > + ----- > + GND > + > +properties: > + compatible: > + const: temperature-transducer > + > + io-channels: > + maxItems: 1 > + description: | > + Channel node of a voltage io-channel. > + > + '#io-channel-cells': > + const: 0 This is a io-channel consumer and producer? > + > + sense-offset-millicelsius: > + description: | > + Temperature offset. The default is <0>. > + This offset is commonly used to convert from Kelvins to degrees Celsius. > + In that case, sense-offset-millicelsius would be set to <(-273150)>. default: 0 > + > + sense-resistor-ohms: > + description: | > + The sense resistor. Defaults to <1>. > + Set sense-resistor-ohms to <1> when using a temperature to voltage > + transducer. default: 1 Though why would we set the value to 1 if the default is 1? > + > + alpha-ppm-per-celsius: > + description: | > + Sometimes referred to as output gain, slope, or temperature coefficient. > + > + alpha is expressed in parts per million which can be micro-amps per > + degrees Celsius or micro-volts per degrees Celsius. The is the main > + characteristic of a temperature transducer and should be stated in the > + datasheet. > + > +additionalProperties: false Blank line here. > +required: > + - compatible > + - io-channels > + - alpha-ppm-per-celsius > + > +examples: > + - | > + ad950: temperature-sensor-0 { > + compatible = "temperature-transducer"; > + #io-channel-cells = <0>; > + io-channels = <&temp_adc 3>; > + > + sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */ > + sense-resistor-ohms = <8060>; > + alpha-ppm-per-celsius = <1>; /* 1 uA/K */ > + }; > + - | > + znq_tmp: temperature-sensor-1 { > + compatible = "temperature-transducer"; > + #io-channel-cells = <0>; > + io-channels = <&temp_adc 2>; > + > + sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */ > + alpha-ppm-per-celsius = <4000>; /* 4 mV/K */ > + }; > +... > -- > 2.30.1.489.g328c10930387 > >
