BUF08821 datasheet(9/28 Pages) TI2

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BUF08821

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SBOS438D

– AUGUST 2008 – REVISED JULY 2011

GENERAL-CALL RESET AND POWER-UP

NONVOLATILE MEMORY

The BUF08821 responds to a General-Call Reset,

BKSEL Pin

which is an address byte of 00h (0000 0000) followed

by a data byte of 06h (0000 0110). The BUF08821

The BUF08821 has 16x rewrite capability for each

acknowledges

both

bytes.

Table

provides

word in the nonvolatile memory. The BUF08821 has

reference for the General-Call Reset command code.

the ability to store two distinct gamma curves in two

Upon receiving a General-Call Reset, the BUF08821

different nonvolatile memory banks, each of which

performs a full internal reset, as though it had been

has 16x rewrite capability. To facilitate fast switching

powered off and then on. It always acknowledges the

between the two distinct gamma curves, two storage

General-Call address byte of 00h (0000 0000), but

registers are implemented for each DAC channel so

does not acknowledge any General-Call data bytes

that there is no delay as a result of reading the

other than 06h (0000 0110).

nonvolatile memory when the banks are switched.

One of the two available banks is selected using the

When the BUF08821 powers up, it automatically

external input pin, BKSEL. When this pin is LOW,

performs a reset. As part of the reset, the BUF08821

BANK0 is selected; when this pin is HIGH, BANK1 is

is configured for all outputs to change to the last

selected.

programmed

nonvolatile

memory

values,

1000000000 if the nonvolatile memory values have

When the BKSEL pin changes state, the BUF08821

not been programmed.

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

OUTPUT VOLTAGE

updated from the nonvolatile memory. This switching

occurs within 5

μs of the BKSEL pin state change,

Buffer output values are determined by the analog

and the outputs settle in less than 5

μs. The total time

supply voltage (VS) and the decimal value of the

to switch from one gamma curve to the other gamma

binary input code used to program that buffer. The

curve is less than 10

μs. This fast switching allows for

value is calculated using Equation 1:

the

easy

implementation

dynamic

gamma

correction using the BUF08821.

(1)

Data from the nonvolatile memory may be fed into the

storage registers by commands issued by the I2C

The BUF08821 outputs are capable of a full-scale

master. The bank to be acquired by the command

voltage

output

change

typically

μs;

from the I2C master depends on the state of the

intermediate steps are required.

BKSEL pin. At power-on, the BUF08821 reads the

values from the nonvolatile memory into the storage

UPDATING THE DAC OUTPUT VOLTAGES

registers. If the I2C interface is used to update the

Because the BUF08821 features a double-buffered

storage registers through write operations, these

structure,

updating

the

digital-to-analog

values remain in the storage registers until the device

converter (DAC) and/or the VCOM register is not the

powers off, they are overwritten by a write command

same as updating the DAC and/or VCOM output

on the I2C interface, or a memory acquire command

voltage. There are two methods for updating the

is issued on the I2C interface. This architecture allows

DAC/VCOM output voltages.

a controller to update the storage registers with two

new gamma curves (one in each bank) without

Method 1: Method 1 is used when it is desirable to

updating the nonvolatile memory, and continue to

have

the

DAC/VCOM

output

voltage

change

change quickly between the two new gamma curves

immediately after writing to a DAC register. For each

by using the BKSEL pin.

write transaction, the master sets data bit 15 to a '1'.

The DAC/VCOM output voltage update occurs after

General Acquire Command

receiving the 16th data bit for the currently-written

A general acquire command is used to update all

registers

and

DAC/VCOM

outputs

the

last

Method 2: Method 2 is used when it is desirable to

programmed values stored in nonvolatile memory for

have all DAC/VCOM output voltages change at the

the

selected

bank.

single-channel

acquire

same time. First, the master writes to the desired

command updates only the register and DAC/VCOM

DAC/VCOM channels with data bit 15 a '0'. Then,

output of the DAC/VCOM that corresponds to the

when writing the last desired DAC/VCOM channel, the

DAC/VCOM address used in the single-channel

master sets data bit 15 to a '1'. All DAC/VCOM

acquire command.

channels are updated at the same time after

receiving the 16th data bit.

These are the steps of the sequence to initiate a

general channel acquire:

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