Datasheet

POR(1.1V)
t (min) ³
F
500 sm t (min) 10 s
R
³ m
V
SD
t
OFF
100 s³ m
BUF12840
www.ti.com SBOS519A –OCTOBER 2010– REVISED JULY 2011
POWER-ON RESET (POR) AUTO READ Immediately after power up, all DAC outputs are set
FUNCTION to 0V. During the auto-read function, values are
written into the DAC registers as they are being read
Figure 14 depicts the BUF12840 POR Master Mode
from the EEPROM. Once the auto-read function is
auto read function and timing. The BUF12840 makes
complete, all values are simultaneously loaded from
the first attempt to read the external EEPROM 5ms
the DAC registers to the DAC outputs. Therefore, all
after the POR (power-on reset) condition is met, as
values change together. This action is performed
shown in Figure 13. Following the initial 5ms wait
regardless of the state of the LD pin and occurs by
period, the BUF12840 queries the EEPROM with a
default after auto-read is completed.
digital word that includes an EEPROM address and
acknowledge request. If communication with the Once the information is downloaded from the
EEPROM is established, the download finishes in EEPROM, the BUF12840 automatically goes into
10ms. slave mode, where all slave mode operations are
supported. The BUF12840 remains in slave mode
However, if the first read attempt is not successful,
until another POR, GCR (general-call reset), or RA
the BUF12840 waits for 1ms and then tries to start
(read again) condition is met.
the download again. This process repeats itself until a
successful acknowledge from the EEPROM is The EN pin should be set to a high level within 15ms
detected or until 10 read attempts have been made. If of crossing the POR condition. If the EN pin active
at any time during this process the BUF12840 does high state is not detected during the first 10 query
detect a successful acknowledge from the EEPROM attempts, the BUF12840 automatically enters slave
and the EN pin is properly set, the BUF12840 initiates mode. If the master mode auto read function must be
the upload and reads the contents of the EEPROM, terminated at any time during the auto read process,
which takes approximately 10ms to complete. The the EN pin can be set to a low '0' level that forces the
DAC outputpower-on reset value is 0V. The state of BUF12840 into slave mode and the automatic
V
S
(analog supply voltage) does not affect POR or download process to stop. If an EEPROM
the auto read function. acknowledge is not detected during the possible 10
read attempts, the BUF12840 automatically goes into
slave mode following the tenth read attempt. Note
that the analog power, V
S
, does not need to be on
during any interface communication.
Figure 13. POR
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