LTC3219_15 Datasheet, PDF (9/20 Pages) Linear Technology – 250mA Universal Nine Channel LED Driver

LTC3219
OPERATION
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.
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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