drivers: led: ltc3220: add README Documentation for LTC3220

Added driver documentation for LTC3220 LED driver

Signed-off-by: Jan Carlo Roleda <[email protected]>

Author: jcroleda

doc/sphinx/source/drivers/led/ltc3220.rst

@@ -0,0 +1 @@
+.. include:: ../../../../../drivers/led/ltc3220/README.rst

doc/sphinx/source/projects_doc.rst

@@ -98,4 +98,12 @@ GYROSCOPES
    :maxdepth: 1
    :glob:
 
-   projects/gyroscope/*
+   projects/gyroscope/*
+
+LED
+============
+.. toctree::
+   :maxdepth: 1
+   :glob:
+
+   projects/led/*

drivers/led/ltc3220/README.rst

@@ -0,0 +1,123 @@
+LTC3220 no-OS driver
+====================
+
+.. no-os-doxygen::
+
+Supported Devices
+-----------------
+
+`LTC3220 <https://www.analog.com/en/products/ltc3220.html>`_
+
+Overview
+--------
+
+The LTC3220 is a highly integrated multi-display LED drivers. 
+These parts contain a high efficiency, low noise charge pump to provide power 
+to up to eighteen universal LED current sources. The LED currents are set by 
+an internal precision current reference. Independent dimming, on/off, 
+blinking and gradation control for all universal current sources is achieved 
+via the I2C serial interface. 6-bit linear DACs are available to adjust 
+brightness levels independently for each universal LED current source.
+
+The LTC3220 charge pump optimizes efficiency based on the voltage 
+across the LED current sources. The part powers up in 1x mode and 
+will automatically switch to boost mode whenever any enabled LED current source 
+begins to enter dropout. The first dropout switches the parts into 1.5x mode 
+and a subsequent dropout switches the LTC3220 into 2x mode. The parts reset to 
+1x mode whenever a data bit is updated via the I2C port.
+
+There are two I2C addresses available. The LTC3220 I2C address is 0011100 
+and the LTC3220-1 I2C address is 0011101. The I2C address is the only difference
+between the LTC3220 and LTC3220-1.
+
+Applications
+------------
+
+* Video Phones with QVGA+ Displays
+* Keypad Lighting
+* General/Miscellaneous Lighting
+
+LTC3220 Device Configuration
+----------------------------
+
+Driver Initialization
+---------------------
+
+In order to be able to use the device, you will have to provide the support for
+the communication protocol (SPI) as mentioned above.
+
+The first API to be called is **ltc3220_init**. Make sure that it returns 0,
+which means that the driver was initialized correctly.
+
+After successful initialization, it is recommended to perform a device reset by
+calling **ltc3220_reset** in order to put the device in a known initial state,
+where all the registers on the device are reset to 0.
+
+ULED Configuration
+-----------------
+
+Each of the 18 LEDs are individually configurable to a specific mode
+of operation and adjustable current output, using a 6-bit DAC
+to provide 64 levels of resolution from 0mA to 20mA.
+
+The supported modes of operation are:
+
+1. Normal - provides a current output for an LED attached to its pins.
+2. Blinking - performs a blinking operation with configurable period and 
+rise time in the Blink Configuration
+3. Gradation - performs a gradation to gradually adjust the current provided to
+the output, configurable to rising or falling and adjusting its ramp time and 
+period.
+4. General Purpouse Output (GPO) - Configures the output to run in current 
+limited mode or as a strong pull-down output if the output current is 0mA.
+
+The ULED registers can be updated by using **ltc3220_set_uled_mode** and
+**ltc3220_set_uled_current**, or together in the respective ULEDs' register via 
+**ltc3220_update_reg_uled**, where the 2 upper bits written correspond to the
+mode of operation, and the 6 lower bits are for the DAC.
+
+If the device command register has quick write set, writing a mode and current
+output level on ULED1 will perform a parallel write to all ULED outputs.
+
+Device Command Configuration
+----------------------------
+
+The device can be forced to operate on a specific charge pump configuration, be
+written to in parallel through ULED1, and be shutdown while maintaining the 
+latest device configuration registers. This can be set individually via 
+**ltc3220_set_quick_write**, **ltc3220_set_cpo_1x**, **ltc3220_set_cpo_1p5x**, 
+**ltc3220_set_cpo_2x**, **ltc3220_set_shutdown**, or directly to the register
+via **ltc3220_update_reg_command**, where the 4 lower bits of the register 
+corresponds to the above set configurations, according to the
+device's datasheet.
+
+Blink Configuration
+-------------------
+
+The blinking mode of operation for ULED outputs can be configured to have a
+longer blinking period and a faster rise time in current. These can be
+configured with **ltc3220_set_blink_fast** and **ltc3220_set_blink_long**, or
+together in the Blink and Gradation Configuration register via 
+**ltc3220_update_reg_blink_grad**. Note that this also configures
+the gradation configuration as they share the same configuration register.
+
+Gradation Configuration
+-----------------------
+
+The gradation mode of operation for ULED outputs can be configured to increase
+or decrease in brightness by gradually adjusting the current output based on an
+internal counter. This counter resets to its maximum when set to decreasing, and
+resets to its minimum when set to increasing. This can be set by using 
+**ltc3220_set_grad_increasing**.
+
+Note that in increasing gradation, the counter remains at its maximum if another
+LED is set to gradation mode. The newly set LED will immediately appear with its
+maximum current and will not rise towards it.
+
+The ramp time and period of gradation is also configurable from disabling
+gradation to a ramp time of 0.96s to 0.24s and a period of 1.25s to 0.313s,
+set by using **ltc3220_set_grad_speed**.
+
+Alternatively these can be set together in the Blink and Gradation Configuration 
+register via **ltc3220_update_reg_blink_grad**. Note that this also configures
+the blink configuration as they share the same configuration register.