BUF08821 Datasheet, PDF (9/27 Pages) Texas Instruments – Programmable Gamma-Voltage Generator and VCOM Calibrator with Integrated Two-Bank Memory

www.ti.com ................................................................................................................................................. SBOS438C – AUGUST 2008 – REVISED AUGUST 2009
GENERAL-CALL RESET AND POWER-UP
The BUF08821 responds to a General-Call Reset,
which is an address byte of 00h (0000 0000) followed
by a data byte of 06h (0000 0110). The BUF08821
acknowledges both bytes. Table 2 provides a
reference for the General-Call Reset command code.
Upon receiving a General-Call Reset, the BUF08821
performs a full internal reset, as though it had been
powered off and then on. It always acknowledges the
General-Call address byte of 00h (0000 0000), but
does not acknowledge any General-Call data bytes
other than 06h (0000 0110).
When the BUF08821 powers up, it automatically
performs a reset. As part of the reset, the BUF08821
is configured for all outputs to change to the last
programmed nonvolatile memory values, or
1000000000 if the nonvolatile memory values have
not been programmed.
OUTPUT VOLTAGE
Buffer output values are determined by the analog
supply voltage (V_S) and the decimal value of the
binary input code used to program that buffer. The
value is calculated using Equation 1:
V_OUT = V_S ´
CODE₁₀
1024
(1)
The BUF08821 outputs are capable of a full-scale
voltage output change in typically 5μs; no
intermediate steps are required.
UPDATING THE DAC OUTPUT VOLTAGES
Because the BUF08821 features a double-buffered
register structure, updating the digital-to-analog
converter (DAC) and/or the V_COM register is not the
same as updating the DAC and/or V_COM output
voltage. There are two methods for updating the
DAC/V_COM output voltages.
Method 1: Method 1 is used when it is desirable to
have the DAC/V_COM output voltage change
immediately after writing to a DAC register. For each
write transaction, the master sets data bit 15 to a '1'.
The DAC/V_COM output voltage update occurs after
receiving the 16th data bit for the currently-written
register.
Method 2: Method 2 is used when it is desirable to
have all DAC/V_COM output voltages change at the
same time. First, the master writes to the desired
DAC/V_COM channels with data bit 15 a '0'. Then,
when writing the last desired DAC/V_COM channel, the
master sets data bit 15 to a '1'. All DAC/V_COM
channels are updated at the same time after
receiving the 16th data bit.
NONVOLATILE MEMORY
BKSEL Pin
The BUF08821 has 16x rewrite capability for each
word in the nonvolatile memory. The BUF08821 has
the ability to store two distinct gamma curves in two
different nonvolatile memory banks, each of which
has 16x rewrite capability. To facilitate fast switching
between the two distinct gamma curves, two storage
registers are implemented for each DAC channel so
that there is no delay as a result of reading the
nonvolatile memory when the banks are switched.
One of the two available banks is selected using the
external input pin, BKSEL. When this pin is LOW,
BANK0 is selected; when this pin is HIGH, BANK1 is
selected.
When the BKSEL pin changes state, the BUF08821
switches all DAC channels simultaneously from the
values in the storage registers for the previously
selected bank to the values in the storage registers
for the new bank. The storage registers are not
updated from the nonvolatile memory. This switching
occurs within 5μs of the BKSEL pin state change,
and the outputs settle in less than 5μs. The total time
to switch from one gamma curve to the other gamma
curve is less than 10μs. This fast switching allows for
the easy implementation of dynamic gamma
correction using the BUF08821.
Data from the nonvolatile memory may be fed into the
storage registers by commands issued by the I²C
master. The bank to be acquired by the command
from the I²C master depends on the state of the
BKSEL pin. At power-on, the BUF08821 reads the
values from the nonvolatile memory into the storage
registers. If the I²C interface is used to update the
storage registers through write operations, these
values remain in the storage registers until the device
powers off, they are overwritten by a write command
on the I²C interface, or a memory acquire command
is issued on the I²C interface. This architecture allows
a controller to update the storage registers with two
new gamma curves (one in each bank) without
updating the nonvolatile memory, and continue to
change quickly between the two new gamma curves
by using the BKSEL pin.
General Acquire Command
A general acquire command is used to update all
registers and DAC/V_COM outputs to the last
programmed values stored in nonvolatile memory for
the selected bank. A single-channel acquire
command updates only the register and DAC/V_COM
output of the DAC/V_COM that corresponds to the
DAC/V_COM address used in the single-channel
acquire command.
Copyright © 2008–2009, Texas Instruments Incorporated
Product Folder Link(s): BUF08821
Submit Documentation Feedback
9