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LTC3207/LTC3207-1
OPERATION
When gradation is disabled the LED output current remains
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.
External Enable Control (ENU)
The ENU pin can be used to enable or disable the LTC3207/
LTC3207-1 without reaccessing the I 2 C 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 preselected displays. LED displays are
controlled with ENU by setting the appropriate data bits in
REG1 to REG12 and control bits in REG14 and REG15.
To use the ENU pin, the I 2 C port must ?rst be con?gured
to select the desired LED outputs. When ENU is high, the
selected displays will be enabled as per the REG14 and
REG15 settings. When ENU is low, the selected displays
will be off. If no other displays are programmed to be
enabled, the chip will be in shutdown.
Gradation can also be preprogrammed for control by
the ENU pin. The registers are written as required per
the gradation description and the UP bit is ignored. The
registers are programmed when ENU is low. When ENU is
set high the part will become enabled and the selected LED
outputs will ramp up. When ENU is set low the selected
LED outputs will ramp low to zero current and then the
part will shut down. The charge pump must be in auto
mode if shutdown is required.
If the ENU pin is not used, it is connected to ground. If
ENU is used and other ULED outputs are active then ENU
will reset the charge pump mode to 1x on the falling edge.
Please refer to Application Note 108 for detailed informa-
tion and examples on programming ENU control.
Shutdown Current
Shutdown occurs when all the current source data bits
have been written to zero, when DV CC is set below the
undervoltage lockout voltage or when ENU switches low
(all other outputs disabled). The charge pump must also
Although the LTC3207/LTC3207-1 are designed to have
very low shutdown current, they will draw about 3.5μA
from V BAT when in shutdown. Internal logic ensures that
the device is in shutdown when DV CC is low. Note, however,
that all of the logic signals that are referenced to DV CC
(SCL, SDA, ENU and CAMHL) will need to be at DV CC
or below (i.e., ground) to avoid violation of the absolute
maximum speci?cations on these pins.
EMI Reduction
The ?ying capacitor pins C1M, C1P, C2M and C2P have
controlled slew rates, in the 5ns to 10ns range, to reduce
conducted and radiated noise.
Serial Port
The microcontroller-compatible I 2 C serial port provides
all of the command and control inputs for the LTC3207/
LTC3207-1. Data on the SDA input is loaded on the rising
edge of SCL. D7 is loaded ?rst and D0 last. There are 16
data registers, one address register and one sub-address
register. Once all address bits have been clocked into the
address register, acknowledge occurs. The sub-address
register is then written, followed by writing the data
register. Each data register has a sub-address. After the
data register has been written, a load pulse is created
after the stop bit. The load pulse transfers all of the data
held in the data registers to the DAC registers. The stop
bit can be delayed until all of the data master registers
have been written. At this point the LED current will be
changed to the new settings. The serial port uses static
logic registers so there is no minimum speed at which it
can be operated.
I 2 C Interface
The LTC3207/LTC3207-1 communicate with a host (master)
using the standard I 2 C 2-wire interface. The Timing Diagram
(Figure 3) shows the timing relationship of the signals on
the bus. The two bus lines, SDA and SCL, must be high
when the bus is not in use. External pull-up resistors or
current sources, such as the LTC1694 SMBus Acceler-
ator, are required on these lines.
be in auto mode.
3207fc
10
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