AD4695 driver¶

ADC driver for Analog Devices Inc. AD4695 and similar devices. The module name is ad4695.

Supported devices¶

The following chips are supported by this driver:

Supported features¶

SPI wiring modes¶

The driver currently supports the following SPI wiring configuration:

4-wire mode¶

In this mode, CNV and CS are tied together and there is a single SDO line.

+-------------+         +-------------+
|          CS |<-+------| CS          |
|         CNV |<-+      |             |
|     ADC     |         |     HOST    |
|             |         |             |
|         SDI |<--------| SDO         |
|         SDO |-------->| SDI         |
|        SCLK |<--------| SCLK        |
+-------------+         +-------------+

To use this mode, in the device tree, omit the cnv-gpios and spi-rx-bus-width properties.

Channel configuration¶

Since the chip supports multiple ways to configure each channel, this must be described in the device tree based on what is actually wired up to the inputs.

There are three typical configurations:

An INx pin is used as the positive input with the REFGND, COM or the next INx pin as the negative input.

Pairing with REFGND¶

Each INx pin can be used as a pseudo-differential input in conjunction with the REFGND pin. The device tree will look like this:

channel@0 {
    reg = <0>; /* IN0 */
};

If no other channel properties are needed (e.g. adi,no-high-z), the channel node can be omitted entirely.

This will appear on the IIO bus as the voltage0 channel. The processed value (raw × scale) will be the voltage present on the IN0 pin relative to REFGND. (Offset is always 0 when pairing with REFGND.)

Pairing with COM¶

Each INx pin can be used as a pseudo-differential input in conjunction with the COM pin. The device tree will look like this:

com-supply = <&vref_div_2>;

channel@1 {
    reg = <1>; /* IN1 */
    common-mode-channel = <AD4695_COMMON_MODE_COM>;
    bipolar;
};

This will appear on the IIO bus as the voltage1 channel. The processed value ((raw + offset) × scale) will be the voltage measured on the IN1 pin relative to REFGND. (The offset is determined by the com-supply voltage.)

The macro comes from:

#include <dt-bindings/iio/adi,ad4695.h>

Pairing two INx pins¶

An even-numbered INx pin and the following odd-numbered INx pin can be used as a pseudo-differential input. The device tree for using IN2 as the positive input and IN3 as the negative input will look like this:

in3-supply = <&vref_div_2>;

channel@2 {
    reg = <2>; /* IN2 */
    common-mode-channel = <3>; /* IN3 */
    bipolar;
};

This will appear on the IIO bus as the voltage2 channel. The processed value ((raw + offset) × scale) will be the voltage measured on the IN1 pin relative to REFGND. (Offset is determined by the in3-supply voltage.)

VCC supply¶

The chip supports being powered by an external LDO via the VCC input or an internal LDO via the LDO_IN input. The driver looks at the device tree to determine which is being used. If ldo-supply is present, then the internal LDO is used. If vcc-supply is present, then the external LDO is used and the internal LDO is disabled.

Reference voltage¶

The chip supports an external reference voltage via the REF input or an internal buffered reference voltage via the REFIN input. The driver looks at the device tree to determine which is being used. If ref-supply is present, then the external reference voltage is used and the internal buffer is disabled. If refin-supply is present, then the internal buffered reference voltage is used.

Gain/offset calibration¶

System calibration is supported using the channel gain and offset registers via the calibscale and calibbias attributes respectively.

Unimplemented features¶

Additional wiring modes
Threshold events
Oversampling
GPIO support
CRC support

Device buffers¶

This driver supports hardware triggered buffers. This uses the “advanced sequencer” feature of the chip to trigger a burst of conversions.

Also see Industrial IIO device buffers for more general information.