Re: [PATCH 1/4] dt-bindings: iio: adc: add ti,ads122c14

[Jonathan Cameron]

On Mon, 15 Jun 2026 16:59:59 -0500
"David Lechner (TI)" <dlechner@xxxxxxxxxxxx> wrote:

> Add new bindings for ti,ads122c14 and similar devices.
> 
> This is an ADC that is primarily intended for use with temperature
> sensors. There are a few unusual properties because of this. In
> particular, the reference voltage source and current output requirements
> can be different for each measurement, so these are included in the
> channel bindings.
> 
> The REFP/REFN reference voltage is usually just connected to a resistor
> that is being driven by the ADC's current outputs, so there is special
> property for this case rather than requiring a regulator to be defined
> to represent that.
> 
> ti,vref-source is reused from ti,tlv320adcx140.yaml (otherwise might
> have preferred an enum of strings).
> 
> Signed-off-by: David Lechner (TI) <dlechner@xxxxxxxxxxxx>

A few queries inline though I'm only just starting to get my head
around this device...

Thanks

Jonathan

> ---
>  .../devicetree/bindings/iio/adc/ti,ads112c14.yaml  | 224 +++++++++++++++++++++
>  MAINTAINERS                                        |   7 +
>  include/dt-bindings/iio/adc/ti,ads112c14.h         |  11 +
>  3 files changed, 242 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads112c14.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads112c14.yaml
> new file mode 100644
> index 000000000000..dc7f37cad772
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/adc/ti,ads112c14.yaml
> @@ -0,0 +1,224 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/adc/ti,ads112c14.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Texas Instruments' ADS112C14 and similar ADC chips
> +
> +description: |
> +  Supports the following Texas Instruments' ADC chips:
> +  - ADS112C14 (16-bit)
> +  - ADS122C14 (24-bit)
> +
> +  https://www.ti.com/lit/ds/symlink/ads122c14.pdf
> +
> +  These chips are primarily designed for use with temperature sensors such as
> +  RTDs and thermocouples. The channel bindings reflect this in that each channel
> +  represents the conditions required to make a measurement rather than strictly
> +  just the physical input channels.
> +
> +maintainers:
> +  - David Lechner <dlechner@xxxxxxxxxxxx>
> +
> +unevaluatedProperties: false
> +
> +properties:
> +  compatible:
> +    enum:
> +      - ti,ads112c14
> +      - ti,ads122c14
> +
> +  reg:
> +    items:
> +      - minimum: 0x40
> +        maximum: 0x47
> +
> +  clocks:
> +    maxItems: 1
> +    description: Optional external clock connected to GPIO3 pin.
> +
> +  avdd-supply: true
> +  dvdd-supply: true
> +
> +  refp-supply: true
> +  refn-supply: true
> +
> +  refp-refn-resistor-ohms:
> +    description:
> +      The resistance of the external resistor between REFP and REFN when using
> +      resistor bridge driven by current outputs for RTD measurements.
> +
> +  interrupts:
> +    minItems: 1
> +    items:
> +      - description: FAULT interrupt (GPIO2 pin)
> +      - description: DRDY interrupt (GPIO3 pin)
> +
> +  interrupt-names:
> +    minItems: 1
> +    maxItems: 2
> +    items:
> +      enum: [fault, drdy]
> +
> +  gpio-controller: true
> +  '#gpio-cells':
> +    const: 2
> +
> +  '#address-cells':
> +    const: 1
> +
> +  '#size-cells':
> +    const: 0
> +
> +patternProperties:
> +  ^channel@[0-7]$:
> +    $ref: adc.yaml
> +
> +    unevaluatedProperties: false
> +
> +    properties:
> +      reg:
> +        maximum: 16 # arbitrary limit, channel@ can be any combination of AIN0-AIN7
> +
> +      single-channel:
> +        maximum: 7
> +
> +      diff-channels:
> +        items:
> +          maximum: 7
> +
> +      bipolar:
> +        description:
> +          Set this flag if the differential input can be negative.

I'd leave that description to adc.yaml   Maybe that doc could be improved though
given it basically says bipolar == bipolar mode ;)

> +
> +      excitation-channels:
> +        description: AINx pins used as current output.
> +        $ref: /schemas/types.yaml#/definitions/uint32-array
> +        minItems: 1
> +        maxItems: 2
> +        items:
> +          maximum: 7
> +
> +      excitation-current-microamp:

There seem to be separate controls. Are their usecases where this needs
to be in array?

> +        description: The current output of the excitation channels in microamps.
> +        minimum: 1
> +        maximum: 1000
> +
> +      current-chopping:
> +        $ref: /schemas/types.yaml#/definitions/flag
> +        description:
> +          If provided, the two excitation channels are to be used with current
> +          chopping enabled.

Can I have a reference for that? My initial read suggests it's the input channels
that are chopped.  For GC_EN
"When enabled, the device automatically swaps
the analog inputs and takes the average of two consecutive conversions to
cancel the internal offset voltage"


> +
> +      ti,vref-source:
> +        description: |
> +          Indicates the source for the reference voltage for this channel.
> +          0 - Internal 2.5V reference
> +          1 - Internal 1.25V reference
> +          2 - External reference (REFP-REFN)
> +          3 - AVDD as reference
> +
> +          For convenience, macros for these values are available in
> +          dt-bindings/iio/adc/ti,ads112c14.h.
> +        $ref: /schemas/types.yaml#/definitions/uint32
> +        maximum: 3
> +        default: 0
> +
> +    dependencies:
> +      excitation-channels: [ excitation-current-microamp ]
> +      excitation-current-microamp: [ excitation-channels ]
> +      current-chopping: [ excitation-channels ]
> +
> +    oneOf:
> +      - required: [ single-channel ]
> +      - required: [ diff-channels ]

> +examples:
> +  - |
> +    #include <dt-bindings/iio/adc/ti,ads112c14.h>
> +
> +    i2c {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        adc@40 {
> +            compatible = "ti,ads112c14";
> +            reg = <0x40>;
> +
> +            avdd-supply = <&avdd>;
> +            dvdd-supply = <&dvdd>;
> +
> +            /* 3-Wire RTD: Two IDACs, One Measurement (AIN1-AIN2) */
> +
> +            refp-refn-resistor-ohms = <500>;
> +
> +            #address-cells = <1>;
> +            #size-cells = <0>;
> +
> +            channel@0 {
> +              reg = <0>;
> +              diff-channels = <1>, <2>;
> +              excitation-channels = <0>, <3>;
> +              excitation-current-microamp = <500>;
> +              current-chopping;
> +              ti,vref-source = <ADS112C14_VREF_SOURCE_EXTERNAL>;
> +              label = "rtd";
> +            };
> +        };
> +    };
> +  - |
> +    #include <dt-bindings/iio/adc/ti,ads112c14.h>
> +
> +    i2c {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        adc@40 {
> +            compatible = "ti,ads112c14";
> +            reg = <0x40>;
> +
> +            avdd-supply = <&avdd>;
> +            dvdd-supply = <&dvdd>;
> +
> +            /* Resistive Bridge Measurement With a Thermistor for Temperature Compensation*/
> +
> +            refp-supply = <&avdd>;
> +
> +            #address-cells = <1>;
> +            #size-cells = <0>;
> +
> +            channel@0 {
> +              reg = <0>;
> +              diff-channels = <6>, <7>;
> +              bipolar;
> +              ti,vref-source = <ADS112C14_VREF_SOURCE_EXTERNAL>;
> +              label = "bridge";
> +            };
> +
> +            channel@1 {
> +              reg = <1>;
> +              diff-channels = <1>, <2>;
> +              ti,vref-source = <ADS112C14_VREF_SOURCE_INTERNAL_2_5V>;
> +              label = "thermistor";

Hmm. I'm interested to see where this goes, but generally when we have
a thermistor we attempt to ultimately convert it to a temperature
channel and I'm not seeing info here to allow us to do that.

> +            };
> +        };
> +    };