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LTC3219EUD-TRPBF Datasheet(PDF) 9 Page - Linear Technology |
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LTC3219EUD-TRPBF Datasheet(HTML) 9 Page - Linear Technology |
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9 / 20 page  LTC3219 9 3219fa Mode Switching The LTC3219 will automatically switch from 1x mode to 1.5x mode and subsequently to 2x mode whenever a dropout condition is detected at an LED pin. Dropout occurs when an active current source voltage becomes too low for the programmed current to be supplied. The mode change will not occur unless dropout has existed for approximately 400μs. This delay will allow the LEDs to warm up and achieve the final LED forward voltage value. The mode will automatically switch back to 1x whenever a register is updated via the I2C port, when gradation completes ramping down, on the falling edge of ENU, and after each blink period. The part can be forced to operate in 1x, 1.5x or 2x mode by writing the appropriate bits into REG0. This feature may be used for powering loads from CPO. Automatic mode switching is diabled. Non-programmed current sources do not affect dropout. In addition, ENU controlled current sources do not affect dropout when ENU is low. Universal Current Sources (ULED1 to ULED9) There are nine universal 28mA current sources. Each cur- rent source has a 6-bit linear DAC for current control. The output current range is 0 to full-scale in 64 steps. Each current source is disabled when an all zero data word is written. The supply current for that source is reduced to zero. Connect unused outputs to ground. ULED1 to ULED9 can also be used as general purpose outputs (GPO). GPO outputs can be used as I2C controlled open-drain drivers. The GPO mode is selected by program- ming REG1 to REG9, Bit 6 and Bit 7 to a logic one. In the GPO mode dropout detection is disabled, output swings to ground will not cause mode switching. OPERATION Blinking Each universal output (ULED1 to ULED9) can be set to blink on for 0.156s or 0.625s with a period of 1.25s or 2.5s via the I2C port. The blinking rate is selected via REG11 and ULED outputs are selected via REG1 to REG9. Blinking and gradation rates are independent. Blink resets the charge pump to 1x mode after each period. Please refer to Application Note 111 for detailed information and programming examples on blinking. Gradation Universal LED outputs ULED1 to ULED9 can be set to have the current ramp up and down at 0.24s, 0.48s and 0.96s rates via the I2C port. Each of these outputs can have either blinking or gradation enabled. The gradation time is set via REG11 and ULED outputs are selected via REG1 to REG9. The ramp direction is controlled via REG0. Setting the UP bit high causes gradation to ramp up, setting this bit to a low causes gradation to ramp down. When gradation is disabled the LED output current re- mains at the programmed value. The gradation enable bit must be cleared when the gradation timer is disabled. The charge pump mode is reset to 1x after gradation completes ramping down. Please refer to Application Note 111 for detailed informa- tion and examples on programming gradation. External Enable Control (ENU) The ENU pin can be used to enable or disable the LTC3219 without re-accessing the I2C port. This might be useful to indicate an incoming phone call without waking the micro-controller. ENU can be programmed to indepen- dently control all pre-selected displays. LED displays are controlled with ENU by setting the appropriate data bits in REG1 to REG9 and control bits in REG10 and REG11. |
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