Datasheet

STAR coTOp de
STARTPin
DNI
4/f
CLK
DRDY
or
t
DR
t
SETTLE
ADS1294, ADS1294R
ADS1296, ADS1296R
ADS1298, ADS1298R
SBAS459I –JANUARY 2010–REVISED JANUARY 2012 www.ti.com
Reset (RESET)
There are two methods to reset the ADS129x: pull the RESET pin low, or send the RESET opcode command.
When using the RESET pin, take it low to force a reset. Make sure to follow the minimum pulse width timing
specifications before taking the RESET pin back high. The RESET command takes effect on the eighth SCLK
falling edge of the opcode command. On reset it takes 18 t
CLK
cycles to complete initialization of the configuration
registers to the default states and start the conversion cycle. Note that an internal RESET is automatically issued
to the digital filter whenever registers CONFIG1 and RESP are set to new values with a WREG command.
START
The START pin must be set high for at least 2 t
CLK
s or the START command sent to begin conversions. When
START is low or if the START command has not been sent, the device does not issue a DRDY signal
(conversions are halted).
When using the START opcode to control conversion, hold the START pin low. The ADS129x feature two modes
to control conversion: continuous mode and single-shot mode. The mode is selected by SINGLE_SHOT (bit 3 of
the CONFIG4 register). In multiple device configurations the START pin is used to synchronize devices (see the
Multiple Device Configuration subsection of the SPI Interface section for more details).
Settling Time
The settling time (t
SETTLE
) is the time it takes for the converter to output fully settled data when START signal is
pulled high. Once START is pulled high, DRDY is also pulled high. The next falling edge of DRDY indicates that
data are ready. Figure 40 shows the timing diagram and Table 9 shows the settling time for different data rates.
The settling time depends on f
CLK
and the decimation ratio (controlled by the DR[2:0] bits in the CONFIG1
register). Table 8 shows the settling time as a function of t
CLK
. Note that when START is held high and there is a
step change in the input signal, it takes 3 × t
DR
for the filter to settle to the new value. Settled data are available
on the fourth DRDY pulse. This time must be considered when trying to measure narrow PACE pulses for PACE
detection.
Figure 40. Settling Time
Table 9. Settling Times for Different Data Rates
DR[2:0] HIGH-RESOLUTION MODE LOW-POWER MODE UNIT
000 296 584 t
CLK
001 584 1160 t
CLK
010 1160 2312 t
CLK
011 2312 4616 t
CLK
100 4616 9224 t
CLK
101 9224 18440 t
CLK
110 18440 36872 t
CLK
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