LTC3220 no-OS driver

See drivers/led/ltc3220 (doxygen) for the Doxygen documentation.

Supported Devices

LTC3220

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 (I2C) 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.

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.