LTC2672

LTC2672 IIO DAC Linux Driver.

The LTC2672 is a family of five-channel, 12-/16-bit current source, digital-to-analog converters (DACs) that provide five high compliance, current source outputs with guaranteed 0.6 V dropout at 200 mA. There are eight current ranges that are programmable per channel with full-scale outputs of up to 300 mA. The channels can be paralleled to allow either ultrafine adjustments of large currents or combined outputs of up to 1.5 A. A dedicated supply pin is provided for each output channel. Each channel can be operated from 2.1 V to VCC, and internal switches allow any output to be pulled to the optional negative supply. The LTC2672 includes a precision integrated 1.25 V reference (10 ppm/°C maximum (LFCSP) or 2.4 ppm/°C nominal (WLCSP)), with the option to use an external reference. The serial peripheral interface (SPI)-compatible, 3‑wire serial interface operates on logic levels as low as 1.71 V and at clock rates as high as 50 MHz.

Supported Devices

• LTC2672

Evaluation Boards

• DC2903A

Description

This is a Linux industrial I/O (Linux Industrial I/O Subsystem) subsystem driver, targeting single-channel serial interface DACs. The industrial I/O subsystem provides a unified framework for drivers for many different types of converters and sensors using a number of different physical interfaces (i2c, spi, etc). See Linux Industrial I/O Subsystem for more information.

Source Code

Status

Source	Mainlined?
git	WIP

Files

Function	File
driver	main?drivers/iio/dac/ltc2664.c
dt-bindings	main?Documentation/devicetree/bindings/iio/dac/adi,ltc2672.yaml

Example platform device initialization

Devicetree

Required devicetree properties:

• compatible: Needs to be adi, followed by the name of the device. E.g. adi,ltc2672

• reg: The chipselect number used for the device

• spi-max-frequency: Maximum SPI clock frequency

• vcc-supply: Analog Supply Voltage Input.

• iovcc-supply: Digital Input/Output Supply Voltage.

• v-neg-supply: Negative Supply Voltage Input.

• Channel nodes with reg, output-range-microamp, and optionally adi,toggle-mode properties.

Optional devicetree properties:

• ref-supply: external reference voltage supply regulator. This should only be set if there is an external reference voltage connected to the REF pin.

adi,toggle-mode:
  description:
    Set the channel as a toggle enabled channel. Toggle operation enables
    fast switching of a DAC output between two different DAC codes without
    any SPI transaction.
  type: boolean

adi,rfsadj-ohms:
  description:
    If FSADJ is tied to VCC, an internal RFSADJ (20 kΩ) is selected, which
    results in nominal output ranges. When an external resistor of 19 kΩ to
    41 kΩ can be used instead by connecting the resistor between FSADJ and
    GND
    it controls the scaling of the ranges, and the internal resistor is
    automatically disconnected.
  minimum: 19000
  maximum: 41000
  default: 20000

Example Overlay	File
Overlay	rpi-6.1.y?arch/arm/boot/dts/overlays/rpi-ltc2672-overlay.dts

Driver testing

Each and every IIO device, typically a hardware chip, has a device folder under /sys/bus/iio/devices/iio:deviceX. Where X is the IIO index of the device. Under every of these directory folders reside a set of files, depending on the characteristics and features of the hardware device in question. These files are consistently generalized and documented in the IIO ABI documentation. In order to determine which IIO deviceX corresponds to which hardware device, the user can read the name file /sys/bus/iio/devices/iio:deviceX/name. In case the sequence in which the iio device drivers are loaded/registered is constant, the numbering is constant and may be known in advance.

root@analog:/> cd /sys/bus/iio/devices/
root@analog:/sys/bus/iio/devices> ls
iio:device0

root@analog:/sys/bus/iio/devices> cd iio\:device0

root@analog:/sys/bus/iio/devices/iio:device0> ls -l
total 0
-r--r--r-- 1 root root 4096 Jul  2 07:20 name
lrwxrwxrwx 1 root root    0 Jul  2 07:20 of_node -> ../../../../../../../../firmware/devicetree/base/soc/spi@7e204000/ltc2672@0
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current0_offset
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current0_powerdown
-r--r--r-- 1 root root 4096 Jul  2 07:20 out_current0_powerdown_mode
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current0_raw
-r--r--r-- 1 root root 4096 Jul  2 07:20 out_current0_raw_available
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current0_scale
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current1_offset
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current1_powerdown
-r--r--r-- 1 root root 4096 Jul  2 07:20 out_current1_powerdown_mode
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current1_raw0
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current1_raw1
-r--r--r-- 1 root root 4096 Jul  2 07:20 out_current1_raw_available
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current1_scale
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current1_symbol
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current1_toggle_en
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current2_offset
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current2_powerdown
-r--r--r-- 1 root root 4096 Jul  2 07:20 out_current2_powerdown_mode
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current2_raw
-r--r--r-- 1 root root 4096 Jul  2 07:20 out_current2_raw_available
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current2_scale
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current3_offset
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current3_powerdown
-r--r--r-- 1 root root 4096 Jul  2 07:20 out_current3_powerdown_mode
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current3_raw
-r--r--r-- 1 root root 4096 Jul  2 07:20 out_current3_raw_available
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current3_scale
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current4_offset
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current4_powerdown
-r--r--r-- 1 root root 4096 Jul  2 07:20 out_current4_powerdown_mode
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current4_raw
-r--r--r-- 1 root root 4096 Jul  2 07:20 out_current4_raw_available
-rw-r--r-- 1 root root 4096 Jul  2 07:20 out_current4_scale
drwxr-xr-x 2 root root    0 Jul  2 07:20 power
lrwxrwxrwx 1 root root    0 Jul  2 07:20 subsystem -> ../../../../../../../../bus/iio
-rw-r--r-- 1 root root 4096 Jul  2 07:20 uevent
-r--r--r-- 1 root root 4096 Jul  2 07:20 waiting_for_supplier
root@analog:/sys/bus/iio/devices/iio:device0#

root@analog:~# iio_info
iio_info version: 0.25 (git tag:b6028fde)
Libiio version: 0.25 (git tag: b6028fd) backends: local xml ip usb
IIO context created with local backend.
Backend version: 0.25 (git tag: b6028fd)
Backend description string: Linux analog 6.10.0-rc5-v7l-embedded+ #1 SMP Sun
Jun 30 21:12:36 BST 2024 armv7l
IIO context has 2 attributes:
        local,kernel: 6.10.0-rc5-v7l-embedded+
        uri: local:
IIO context has 3 devices:
        hwmon0: cpu_thermal
                1 channels found:
                        temp1:  (input)
                        1 channel-specific attributes found:
                                attr  0: input value: 49660
                No trigger on this device
        hwmon1: rpi_volt
                1 channels found:
                        in0:  (input)
                        1 channel-specific attributes found:
                                attr  0: lcrit_alarm value: 0
                No trigger on this device
        iio:device0: ltc2672
                5 channels found:
                        current2:  (output)
                        6 channel-specific attributes found:
                                attr  0: offset value: 0
                                attr  1: powerdown value: 0
                                attr  2: powerdown_mode value: 42kohm_to_gnd
                                attr  3: raw value: 0
                                attr  4: raw_available value: [0 1 65535]
                                attr  5: scale value: 4.577636718
                        current1:  (output)
                        9 channel-specific attributes found:
                                attr  0: offset value: 0
                                attr  1: powerdown value: 0
                                attr  2: powerdown_mode value: 42kohm_to_gnd
                                attr  3: raw0 value: 0
                                attr  4: raw1 value: 0
                                attr  5: raw_available value: [0 1 65535]
                                attr  6: scale value: 3.051757812
                                attr  7: symbol value: 0
                                attr  8: toggle_en value: 0
                        current4:  (output)
                        6 channel-specific attributes found:
                                attr  0: offset value: 0
                                attr  1: powerdown value: 0
                                attr  2: powerdown_mode value: 42kohm_to_gnd
                                attr  3: raw value: 0
                                attr  4: raw_available value: [0 1 65535]
                                attr  5: scale value: 4.577636718
                        current3:  (output)
                        6 channel-specific attributes found:
                                attr  0: offset value: 0
                                attr  1: powerdown value: 0
                                attr  2: powerdown_mode value: 42kohm_to_gnd
                                attr  3: raw value: 0
                                attr  4: raw_available value: [0 1 65535]
                                attr  5: scale value: 4.577636718
                        current0:  (output)
                        6 channel-specific attributes found:
                                attr  0: offset value: 0
                                attr  1: powerdown value: 0
                                attr  2: powerdown_mode value: 42kohm_to_gnd
                                attr  3: raw value: 0
                                attr  4: raw_available value: [0 1 65535]
                                attr  5: scale value: 4.577636718
                1 device-specific attributes found:
                                attr  0: waiting_for_supplier value: 0
                1 debug attributes found:
                                debug attr  0: direct_reg_access ERROR:
                                Operation not supported (95)
                No trigger on this device
root@analog:~#

Show device name

root@analog:/sys/bus/iio/devices/iio:device0> cat name
ltc2672

Show scale

Description: Scale to be applied to out_currentY_raw in order to obtain the measured current in microamps.

root@analog:/sys/bus/iio/devices/iio:device0> cat out_current0_scale
4.577636718

Show offset

Description:

/sys/bus/iio/devices/iio:deviceX/out_offset_raw

Raw offset to be applied to out_currentY_raw in order to obtain the measured current in microamps. The offset is applied before scale is applied.

root@analog:/sys/bus/iio/devices/iio:device0>  cat out_current0_offset
0

Set channel Y output current

Description: /sys/bus/iio/devices/iio:deviceX/out_currentY_raw

Raw (unscaled, no bias etc.) output current for channel Y.

root@analog:/sys/bus/iio/devices/iio:device0> echo 10000 > out_current0_raw

I = (out_current0_raw + out_current0_offset) * out_current0_scale = (10000 - 0) * 4.577636718μA = 45,776.367 μA

Enable power down mode on output Y

/sys/bus/iio/devices/iio:deviceX/out_currentY_powerdown

Description: Writing 1 causes output Y to enter the power down mode. Clearing returns to normal operation.

root@analog:/sys/bus/iio/devices/iio:device0> echo 1 > out_current0_powerdown
root@analog:/sys/bus/iio/devices/iio:device0> cat out_current0_powerdown
1
root@analog:/sys/bus/iio/devices/iio:device0> echo 0 > out_current0_powerdown
root@analog:/sys/bus/iio/devices/iio:device0> cat out_current0_powerdown
0

Hardware Interface

Using:

• DC2903A LTC2672-16 Demo Board

• Raspberry Pi 4

Wiring/Connection

Demo Board	RPI4
SCK	SCLK SPI0
SDO	MISO SPI0
SDI	MOSI SPIO
CS	CE SPIO
VCC	5V
GND	GND
LDAC	5V
TGP	5V

More Information

• IIO mailing list: linux-iio@vger.kernel.org

• IIO Linux Kernel Documentation sysfs-bus-iio-*

• IIO Documentation

• IIO Oscilloscope

• Libiio

• About libiio

• IIO High Speed

• Software Defined Radio using the IIO framework

• libiio introduction