BUF16821 datasheet(10/29 Pages) EPCOS

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DATA RATES

OUTPUT VOLTAGE

OUT

CODE

1024

(1)

UPDATING THE DAC OUTPUT VOLTAGES

GENERAL-CALL RESET AND POWER-UP

NONVOLATILE MEMORY

BKSEL Pin

BUF16821

SBOS428 – JULY 2008 ...................................................................................................................................................................................................... www.ti.com

The two-wire bus operates in one of three speed

Buffer output values are determined by the analog

modes:

supply voltage (VS) and the decimal value of the

binary input code used to program that buffer. The

• Standard: allows a clock frequency of up to

value is calculated using Equation 1:

100kHz;

• Fast: allows a clock frequency of up to 400kHz;

and

• High-speed mode (also called Hs mode): allows a

clock frequency of up to 3.4MHz.

The BUF16821 outputs are capable of a full-scale

voltage

output

change

typically

µs; no

The BUF16821 is fully compatible with all three

intermediate steps are required.

modes. No special action is required to use the

device in Standard or Fast modes, but High-speed

mode must be activated. To activate High-speed

mode, send a special address byte of 00001 xxx, with

Because the BUF16821 features a double-buffered

SCL

≤ 400kHz, following the START condition; where

structure,

updating

the

digital-to-analog

xxx are bits unique to the Hs-capable master, which

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

can be any value. This byte is called the Hs master

same as updating the DAC and/or VCOM output

code.

Table

provides

reference

for

the

voltage. There are two methods for updating the

High-speed mode command code. (Note that this

DAC/VCOM output voltages.

configuration

different

from

normal

address

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

bytes—the low bit does not indicate read/write

have

the

DAC/VCOM

output

voltage

change

status.) The BUF16821 responds to the High-speed

immediately after writing to a DAC register. For each

command regardless of the value of these last three

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

bits. The BUF16821 does not acknowledge this byte;

The DAC/VCOM output voltage update occurs after

the

communication

protocol

prohibits

receiving the 16th data bit for the currently-written

acknowledgement of the Hs master code. Upon

receiving a master code, the BUF16821 switches on

its Hs mode filters, and communicates at up to

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

3.4MHz. Additional high-speed transfers may be

have all DAC/VCOM output voltages change at the

initiated without resending the Hs mode byte by

same time. First, the master writes to the desired

generating a repeat START without a STOP. The

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

BUF16821 switches out of Hs mode with the next

when writing the last desired DAC/VCOM channel, the

STOP condition.

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

channels are updated at the same time after

receiving the 16th data bit.

The BUF16821 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 BUF16821

acknowledges

both

bytes.

Table

provides

reference for the General-Call Reset command code.

The BUF16821 has 16x rewrite capability of the

Upon receiving a General-Call Reset, the BUF16821

nonvolatile memory. Additionally, the BUF16821 has

performs a full internal reset, as though it had been

the ability to store two distinct gamma curves in two

powered off and then on. It always acknowledges the

different nonvolatile memory banks, each of which

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

has 16x rewrite capability. One of the two available

does not acknowledge any General-Call data bytes

banks is selected using the external input pin,

other than 06h (0000 0110).

BKSEL. When this pin is low, BANK0 is selected;

when this pin is high, BANK1 is selected.

When the BUF16821 powers up, it automatically

performs a reset. As part of the reset, the BUF16821

is configured for all outputs to change to the last

programmed

nonvolatile

memory

values,

1000000000 if the nonvolatile memory values have

not been programmed.

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